Add m-esr52 at 52.6.0

1 files changed, 1896 insertions, 0 deletions

diff --git a/toolkit/components/telemetry/TelemetryScalar.cpp b/toolkit/components/telemetry/TelemetryScalar.cpp
new file mode 100644
index 000000000..6e9558070
--- /dev/null
+++ b/toolkit/components/telemetry/TelemetryScalar.cpp
@@ -0,0 +1,1896 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "nsITelemetry.h"
+#include "nsIVariant.h"
+#include "nsVariant.h"
+#include "nsHashKeys.h"
+#include "nsBaseHashtable.h"
+#include "nsClassHashtable.h"
+#include "nsIXPConnect.h"
+#include "nsContentUtils.h"
+#include "nsThreadUtils.h"
+#include "mozilla/StaticMutex.h"
+#include "mozilla/Unused.h"
+
+#include "TelemetryCommon.h"
+#include "TelemetryScalar.h"
+#include "TelemetryScalarData.h"
+
+using mozilla::StaticMutex;
+using mozilla::StaticMutexAutoLock;
+using mozilla::Telemetry::Common::AutoHashtable;
+using mozilla::Telemetry::Common::IsExpiredVersion;
+using mozilla::Telemetry::Common::CanRecordDataset;
+using mozilla::Telemetry::Common::IsInDataset;
+using mozilla::Telemetry::Common::LogToBrowserConsole;
+
+////////////////////////////////////////////////////////////////////////
+////////////////////////////////////////////////////////////////////////
+//
+// Naming: there are two kinds of functions in this file:
+//
+// * Functions named internal_*: these can only be reached via an
+//   interface function (TelemetryScalar::*). They expect the interface
+//   function to have acquired |gTelemetryScalarsMutex|, so they do not
+//   have to be thread-safe.
+//
+// * Functions named TelemetryScalar::*. This is the external interface.
+//   Entries and exits to these functions are serialised using
+//   |gTelemetryScalarsMutex|.
+//
+// Avoiding races and deadlocks:
+//
+// All functions in the external interface (TelemetryScalar::*) are
+// serialised using the mutex |gTelemetryScalarsMutex|. This means
+// that the external interface is thread-safe, and many of the
+// internal_* functions can ignore thread safety. But it also brings
+// a danger of deadlock if any function in the external interface can
+// get back to that interface. That is, we will deadlock on any call
+// chain like this
+//
+// TelemetryScalar::* -> .. any functions .. -> TelemetryScalar::*
+//
+// To reduce the danger of that happening, observe the following rules:
+//
+// * No function in TelemetryScalar::* may directly call, nor take the
+//   address of, any other function in TelemetryScalar::*.
+//
+// * No internal function internal_* may call, nor take the address
+//   of, any function in TelemetryScalar::*.
+
+////////////////////////////////////////////////////////////////////////
+////////////////////////////////////////////////////////////////////////
+//
+// PRIVATE TYPES
+
+namespace {
+
+const uint32_t kMaximumNumberOfKeys = 100;
+const uint32_t kMaximumKeyStringLength = 70;
+const uint32_t kMaximumStringValueLength = 50;
+const uint32_t kScalarCount =
+  static_cast<uint32_t>(mozilla::Telemetry::ScalarID::ScalarCount);
+
+enum class ScalarResult : uint8_t {
+  // Nothing went wrong.
+  Ok,
+  // General Scalar Errors
+  OperationNotSupported,
+  InvalidType,
+  InvalidValue,
+  // Keyed Scalar Errors
+  KeyTooLong,
+  TooManyKeys,
+  // String Scalar Errors
+  StringTooLong,
+  // Unsigned Scalar Errors
+  UnsignedNegativeValue,
+  UnsignedTruncatedValue
+};
+
+typedef nsBaseHashtableET<nsDepCharHashKey, mozilla::Telemetry::ScalarID>
+          CharPtrEntryType;
+
+typedef AutoHashtable<CharPtrEntryType> ScalarMapType;
+
+/**
+ * Map the error codes used internally to NS_* error codes.
+ * @param aSr The error code used internally in this module.
+ * @return {nsresult} A NS_* error code.
+ */
+nsresult
+MapToNsResult(ScalarResult aSr)
+{
+  switch (aSr) {
+    case ScalarResult::Ok:
+      return NS_OK;
+    case ScalarResult::OperationNotSupported:
+      return NS_ERROR_NOT_AVAILABLE;
+    case ScalarResult::StringTooLong:
+      // We don't want to throw if we're setting a string that is too long.
+      return NS_OK;
+    case ScalarResult::InvalidType:
+    case ScalarResult::InvalidValue:
+    case ScalarResult::KeyTooLong:
+      return NS_ERROR_ILLEGAL_VALUE;
+    case ScalarResult::TooManyKeys:
+      return NS_ERROR_FAILURE;
+    case ScalarResult::UnsignedNegativeValue:
+    case ScalarResult::UnsignedTruncatedValue:
+      // We shouldn't throw if trying to set a negative number or are truncated,
+      // only warn the user.
+      return NS_OK;
+  }
+  return NS_ERROR_FAILURE;
+}
+
+bool
+IsValidEnumId(mozilla::Telemetry::ScalarID aID)
+{
+  return aID < mozilla::Telemetry::ScalarID::ScalarCount;
+}
+
+// Implements the methods for ScalarInfo.
+const char *
+ScalarInfo::name() const
+{
+  return &gScalarsStringTable[this->name_offset];
+}
+
+const char *
+ScalarInfo::expiration() const
+{
+  return &gScalarsStringTable[this->expiration_offset];
+}
+
+/**
+ * The base scalar object, that servers as a common ancestor for storage
+ * purposes.
+ */
+class ScalarBase
+{
+public:
+  virtual ~ScalarBase() {};
+
+  // Set, Add and SetMaximum functions as described in the Telemetry IDL.
+  virtual ScalarResult SetValue(nsIVariant* aValue) = 0;
+  virtual ScalarResult AddValue(nsIVariant* aValue) { return ScalarResult::OperationNotSupported; }
+  virtual ScalarResult SetMaximum(nsIVariant* aValue) { return ScalarResult::OperationNotSupported; }
+
+  // Convenience methods used by the C++ API.
+  virtual void SetValue(uint32_t aValue) { mozilla::Unused << HandleUnsupported(); }
+  virtual ScalarResult SetValue(const nsAString& aValue) { return HandleUnsupported(); }
+  virtual void SetValue(bool aValue) { mozilla::Unused << HandleUnsupported(); }
+  virtual void AddValue(uint32_t aValue) { mozilla::Unused << HandleUnsupported(); }
+  virtual void SetMaximum(uint32_t aValue) { mozilla::Unused << HandleUnsupported(); }
+
+  // GetValue is used to get the value of the scalar when persisting it to JS.
+  virtual nsresult GetValue(nsCOMPtr<nsIVariant>& aResult) const = 0;
+
+  // To measure the memory stats.
+  virtual size_t SizeOfIncludingThis(mozilla::MallocSizeOf aMallocSizeOf) const = 0;
+
+private:
+  ScalarResult HandleUnsupported() const;
+};
+
+ScalarResult
+ScalarBase::HandleUnsupported() const
+{
+  MOZ_ASSERT(false, "This operation is not support for this scalar type.");
+  return ScalarResult::OperationNotSupported;
+}
+
+/**
+ * The implementation for the unsigned int scalar type.
+ */
+class ScalarUnsigned : public ScalarBase
+{
+public:
+  using ScalarBase::SetValue;
+
+  ScalarUnsigned() : mStorage(0) {};
+  ~ScalarUnsigned() {};
+
+  ScalarResult SetValue(nsIVariant* aValue) final;
+  void SetValue(uint32_t aValue) final;
+  ScalarResult AddValue(nsIVariant* aValue) final;
+  void AddValue(uint32_t aValue) final;
+  ScalarResult SetMaximum(nsIVariant* aValue) final;
+  void SetMaximum(uint32_t aValue) final;
+  nsresult GetValue(nsCOMPtr<nsIVariant>& aResult) const final;
+  size_t SizeOfIncludingThis(mozilla::MallocSizeOf aMallocSizeOf) const final;
+
+private:
+  uint32_t mStorage;
+
+  ScalarResult CheckInput(nsIVariant* aValue);
+
+  // Prevent copying.
+  ScalarUnsigned(const ScalarUnsigned& aOther) = delete;
+  void operator=(const ScalarUnsigned& aOther) = delete;
+};
+
+ScalarResult
+ScalarUnsigned::SetValue(nsIVariant* aValue)
+{
+  ScalarResult sr = CheckInput(aValue);
+  if (sr == ScalarResult::UnsignedNegativeValue) {
+    return sr;
+  }
+
+  if (NS_FAILED(aValue->GetAsUint32(&mStorage))) {
+    return ScalarResult::InvalidValue;
+  }
+  return sr;
+}
+
+void
+ScalarUnsigned::SetValue(uint32_t aValue)
+{
+  mStorage = aValue;
+}
+
+ScalarResult
+ScalarUnsigned::AddValue(nsIVariant* aValue)
+{
+  ScalarResult sr = CheckInput(aValue);
+  if (sr == ScalarResult::UnsignedNegativeValue) {
+    return sr;
+  }
+
+  uint32_t newAddend = 0;
+  nsresult rv = aValue->GetAsUint32(&newAddend);
+  if (NS_FAILED(rv)) {
+    return ScalarResult::InvalidValue;
+  }
+  mStorage += newAddend;
+  return sr;
+}
+
+void
+ScalarUnsigned::AddValue(uint32_t aValue)
+{
+  mStorage += aValue;
+}
+
+ScalarResult
+ScalarUnsigned::SetMaximum(nsIVariant* aValue)
+{
+  ScalarResult sr = CheckInput(aValue);
+  if (sr == ScalarResult::UnsignedNegativeValue) {
+    return sr;
+  }
+
+  uint32_t newValue = 0;
+  nsresult rv = aValue->GetAsUint32(&newValue);
+  if (NS_FAILED(rv)) {
+    return ScalarResult::InvalidValue;
+  }
+  if (newValue > mStorage) {
+    mStorage = newValue;
+  }
+  return sr;
+}
+
+void
+ScalarUnsigned::SetMaximum(uint32_t aValue)
+{
+  if (aValue > mStorage) {
+    mStorage = aValue;
+  }
+}
+
+nsresult
+ScalarUnsigned::GetValue(nsCOMPtr<nsIVariant>& aResult) const
+{
+  nsCOMPtr<nsIWritableVariant> outVar(new nsVariant());
+  nsresult rv = outVar->SetAsUint32(mStorage);
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+  aResult = outVar.forget();
+  return NS_OK;
+}
+
+size_t
+ScalarUnsigned::SizeOfIncludingThis(mozilla::MallocSizeOf aMallocSizeOf) const
+{
+  return aMallocSizeOf(this);
+}
+
+ScalarResult
+ScalarUnsigned::CheckInput(nsIVariant* aValue)
+{
+  // If this is a floating point value/double, we will probably get truncated.
+  uint16_t type;
+  aValue->GetDataType(&type);
+  if (type == nsIDataType::VTYPE_FLOAT ||
+      type == nsIDataType::VTYPE_DOUBLE) {
+    return ScalarResult::UnsignedTruncatedValue;
+  }
+
+  int32_t signedTest;
+  // If we're able to cast the number to an int, check its sign.
+  // Warn the user if he's trying to set the unsigned scalar to a negative
+  // number.
+  if (NS_SUCCEEDED(aValue->GetAsInt32(&signedTest)) &&
+      signedTest < 0) {
+    return ScalarResult::UnsignedNegativeValue;
+  }
+  return ScalarResult::Ok;
+}
+
+/**
+ * The implementation for the string scalar type.
+ */
+class ScalarString : public ScalarBase
+{
+public:
+  using ScalarBase::SetValue;
+
+  ScalarString() : mStorage(EmptyString()) {};
+  ~ScalarString() {};
+
+  ScalarResult SetValue(nsIVariant* aValue) final;
+  ScalarResult SetValue(const nsAString& aValue) final;
+  nsresult GetValue(nsCOMPtr<nsIVariant>& aResult) const final;
+  size_t SizeOfIncludingThis(mozilla::MallocSizeOf aMallocSizeOf) const final;
+
+private:
+  nsString mStorage;
+
+  // Prevent copying.
+  ScalarString(const ScalarString& aOther) = delete;
+  void operator=(const ScalarString& aOther) = delete;
+};
+
+ScalarResult
+ScalarString::SetValue(nsIVariant* aValue)
+{
+  // Check that we got the correct data type.
+  uint16_t type;
+  aValue->GetDataType(&type);
+  if (type != nsIDataType::VTYPE_CHAR &&
+      type != nsIDataType::VTYPE_WCHAR &&
+      type != nsIDataType::VTYPE_DOMSTRING &&
+      type != nsIDataType::VTYPE_CHAR_STR &&
+      type != nsIDataType::VTYPE_WCHAR_STR &&
+      type != nsIDataType::VTYPE_STRING_SIZE_IS &&
+      type != nsIDataType::VTYPE_WSTRING_SIZE_IS &&
+      type != nsIDataType::VTYPE_UTF8STRING &&
+      type != nsIDataType::VTYPE_CSTRING &&
+      type != nsIDataType::VTYPE_ASTRING) {
+    return ScalarResult::InvalidType;
+  }
+
+  nsAutoString convertedString;
+  nsresult rv = aValue->GetAsAString(convertedString);
+  if (NS_FAILED(rv)) {
+    return ScalarResult::InvalidValue;
+  }
+  return SetValue(convertedString);
+};
+
+ScalarResult
+ScalarString::SetValue(const nsAString& aValue)
+{
+  mStorage = Substring(aValue, 0, kMaximumStringValueLength);
+  if (aValue.Length() > kMaximumStringValueLength) {
+    return ScalarResult::StringTooLong;
+  }
+  return ScalarResult::Ok;
+}
+
+nsresult
+ScalarString::GetValue(nsCOMPtr<nsIVariant>& aResult) const
+{
+  nsCOMPtr<nsIWritableVariant> outVar(new nsVariant());
+  nsresult rv = outVar->SetAsAString(mStorage);
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+  aResult = outVar.forget();
+  return NS_OK;
+}
+
+size_t
+ScalarString::SizeOfIncludingThis(mozilla::MallocSizeOf aMallocSizeOf) const
+{
+  size_t n = aMallocSizeOf(this);
+  n+= mStorage.SizeOfExcludingThisIfUnshared(aMallocSizeOf);
+  return n;
+}
+
+/**
+ * The implementation for the boolean scalar type.
+ */
+class ScalarBoolean : public ScalarBase
+{
+public:
+  using ScalarBase::SetValue;
+
+  ScalarBoolean() : mStorage(false) {};
+  ~ScalarBoolean() {};
+
+  ScalarResult SetValue(nsIVariant* aValue) final;
+  void SetValue(bool aValue) final;
+  nsresult GetValue(nsCOMPtr<nsIVariant>& aResult) const final;
+  size_t SizeOfIncludingThis(mozilla::MallocSizeOf aMallocSizeOf) const final;
+
+private:
+  bool mStorage;
+
+  // Prevent copying.
+  ScalarBoolean(const ScalarBoolean& aOther) = delete;
+  void operator=(const ScalarBoolean& aOther) = delete;
+};
+
+ScalarResult
+ScalarBoolean::SetValue(nsIVariant* aValue)
+{
+  // Check that we got the correct data type.
+  uint16_t type;
+  aValue->GetDataType(&type);
+  if (type != nsIDataType::VTYPE_BOOL &&
+      type != nsIDataType::VTYPE_INT8 &&
+      type != nsIDataType::VTYPE_INT16 &&
+      type != nsIDataType::VTYPE_INT32 &&
+      type != nsIDataType::VTYPE_INT64 &&
+      type != nsIDataType::VTYPE_UINT8 &&
+      type != nsIDataType::VTYPE_UINT16 &&
+      type != nsIDataType::VTYPE_UINT32 &&
+      type != nsIDataType::VTYPE_UINT64) {
+    return ScalarResult::InvalidType;
+  }
+
+  if (NS_FAILED(aValue->GetAsBool(&mStorage))) {
+    return ScalarResult::InvalidValue;
+  }
+  return ScalarResult::Ok;
+};
+
+void
+ScalarBoolean::SetValue(bool aValue)
+{
+  mStorage = aValue;
+}
+
+nsresult
+ScalarBoolean::GetValue(nsCOMPtr<nsIVariant>& aResult) const
+{
+  nsCOMPtr<nsIWritableVariant> outVar(new nsVariant());
+  nsresult rv = outVar->SetAsBool(mStorage);
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+  aResult = outVar.forget();
+  return NS_OK;
+}
+
+size_t
+ScalarBoolean::SizeOfIncludingThis(mozilla::MallocSizeOf aMallocSizeOf) const
+{
+  return aMallocSizeOf(this);
+}
+
+/**
+ * Allocate a scalar class given the scalar info.
+ *
+ * @param aInfo The informations for the scalar coming from the definition file.
+ * @return nullptr if the scalar type is unknown, otherwise a valid pointer to the
+ *         scalar type.
+ */
+ScalarBase*
+internal_ScalarAllocate(uint32_t aScalarKind)
+{
+  ScalarBase* scalar = nullptr;
+  switch (aScalarKind) {
+  case nsITelemetry::SCALAR_COUNT:
+    scalar = new ScalarUnsigned();
+    break;
+  case nsITelemetry::SCALAR_STRING:
+    scalar = new ScalarString();
+    break;
+  case nsITelemetry::SCALAR_BOOLEAN:
+    scalar = new ScalarBoolean();
+    break;
+  default:
+    MOZ_ASSERT(false, "Invalid scalar type");
+  }
+  return scalar;
+}
+
+/**
+ * The implementation for the keyed scalar type.
+ */
+class KeyedScalar
+{
+public:
+  typedef mozilla::Pair<nsCString, nsCOMPtr<nsIVariant>> KeyValuePair;
+
+  explicit KeyedScalar(uint32_t aScalarKind) : mScalarKind(aScalarKind) {};
+  ~KeyedScalar() {};
+
+  // Set, Add and SetMaximum functions as described in the Telemetry IDL.
+  // These methods implicitly instantiate a Scalar[*] for each key.
+  ScalarResult SetValue(const nsAString& aKey, nsIVariant* aValue);
+  ScalarResult AddValue(const nsAString& aKey, nsIVariant* aValue);
+  ScalarResult SetMaximum(const nsAString& aKey, nsIVariant* aValue);
+
+  // Convenience methods used by the C++ API.
+  void SetValue(const nsAString& aKey, uint32_t aValue);
+  void SetValue(const nsAString& aKey, bool aValue);
+  void AddValue(const nsAString& aKey, uint32_t aValue);
+  void SetMaximum(const nsAString& aKey, uint32_t aValue);
+
+  // GetValue is used to get the key-value pairs stored in the keyed scalar
+  // when persisting it to JS.
+  nsresult GetValue(nsTArray<KeyValuePair>& aValues) const;
+
+  // To measure the memory stats.
+  size_t SizeOfIncludingThis(mozilla::MallocSizeOf aMallocSizeOf);
+
+private:
+  typedef nsClassHashtable<nsCStringHashKey, ScalarBase> ScalarKeysMapType;
+
+  ScalarKeysMapType mScalarKeys;
+  const uint32_t mScalarKind;
+
+  ScalarResult GetScalarForKey(const nsAString& aKey, ScalarBase** aRet);
+};
+
+ScalarResult
+KeyedScalar::SetValue(const nsAString& aKey, nsIVariant* aValue)
+{
+  ScalarBase* scalar = nullptr;
+  ScalarResult sr = GetScalarForKey(aKey, &scalar);
+  if (sr != ScalarResult::Ok) {
+    return sr;
+  }
+
+  return scalar->SetValue(aValue);
+}
+
+ScalarResult
+KeyedScalar::AddValue(const nsAString& aKey, nsIVariant* aValue)
+{
+  ScalarBase* scalar = nullptr;
+  ScalarResult sr = GetScalarForKey(aKey, &scalar);
+  if (sr != ScalarResult::Ok) {
+    return sr;
+  }
+
+  return scalar->AddValue(aValue);
+}
+
+ScalarResult
+KeyedScalar::SetMaximum(const nsAString& aKey, nsIVariant* aValue)
+{
+  ScalarBase* scalar = nullptr;
+  ScalarResult sr = GetScalarForKey(aKey, &scalar);
+  if (sr != ScalarResult::Ok) {
+    return sr;
+  }
+
+  return scalar->SetMaximum(aValue);
+}
+
+void
+KeyedScalar::SetValue(const nsAString& aKey, uint32_t aValue)
+{
+  ScalarBase* scalar = nullptr;
+  ScalarResult sr = GetScalarForKey(aKey, &scalar);
+  if (sr != ScalarResult::Ok) {
+    MOZ_ASSERT(false, "Key too long or too many keys are recorded in the scalar.");
+    return;
+  }
+
+  return scalar->SetValue(aValue);
+}
+
+void
+KeyedScalar::SetValue(const nsAString& aKey, bool aValue)
+{
+  ScalarBase* scalar = nullptr;
+  ScalarResult sr = GetScalarForKey(aKey, &scalar);
+  if (sr != ScalarResult::Ok) {
+    MOZ_ASSERT(false, "Key too long or too many keys are recorded in the scalar.");
+    return;
+  }
+
+  return scalar->SetValue(aValue);
+}
+
+void
+KeyedScalar::AddValue(const nsAString& aKey, uint32_t aValue)
+{
+  ScalarBase* scalar = nullptr;
+  ScalarResult sr = GetScalarForKey(aKey, &scalar);
+  if (sr != ScalarResult::Ok) {
+    MOZ_ASSERT(false, "Key too long or too many keys are recorded in the scalar.");
+    return;
+  }
+
+  return scalar->AddValue(aValue);
+}
+
+void
+KeyedScalar::SetMaximum(const nsAString& aKey, uint32_t aValue)
+{
+  ScalarBase* scalar = nullptr;
+  ScalarResult sr = GetScalarForKey(aKey, &scalar);
+  if (sr != ScalarResult::Ok) {
+    MOZ_ASSERT(false, "Key too long or too many keys are recorded in the scalar.");
+    return;
+  }
+
+  return scalar->SetMaximum(aValue);
+}
+
+/**
+ * Get a key-value array with the values for the Keyed Scalar.
+ * @param aValue The array that will hold the key-value pairs.
+ * @return {nsresult} NS_OK or an error value as reported by the
+ *         the specific scalar objects implementations (e.g.
+ *         ScalarUnsigned).
+ */
+nsresult
+KeyedScalar::GetValue(nsTArray<KeyValuePair>& aValues) const
+{
+  for (auto iter = mScalarKeys.ConstIter(); !iter.Done(); iter.Next()) {
+    ScalarBase* scalar = static_cast<ScalarBase*>(iter.Data());
+
+    // Get the scalar value.
+    nsCOMPtr<nsIVariant> scalarValue;
+    nsresult rv = scalar->GetValue(scalarValue);
+    if (NS_FAILED(rv)) {
+      return rv;
+    }
+
+    // Append it to value list.
+    aValues.AppendElement(mozilla::MakePair(nsCString(iter.Key()), scalarValue));
+  }
+
+  return NS_OK;
+}
+
+/**
+ * Get the scalar for the referenced key.
+ * If there's no such key, instantiate a new Scalar object with the
+ * same type of the Keyed scalar and create the key.
+ */
+ScalarResult
+KeyedScalar::GetScalarForKey(const nsAString& aKey, ScalarBase** aRet)
+{
+  if (aKey.Length() >= kMaximumKeyStringLength) {
+    return ScalarResult::KeyTooLong;
+  }
+
+  if (mScalarKeys.Count() >= kMaximumNumberOfKeys) {
+    return ScalarResult::TooManyKeys;
+  }
+
+  NS_ConvertUTF16toUTF8 utf8Key(aKey);
+
+  ScalarBase* scalar = nullptr;
+  if (mScalarKeys.Get(utf8Key, &scalar)) {
+    *aRet = scalar;
+    return ScalarResult::Ok;
+  }
+
+  scalar = internal_ScalarAllocate(mScalarKind);
+  if (!scalar) {
+    return ScalarResult::InvalidType;
+  }
+
+  mScalarKeys.Put(utf8Key, scalar);
+
+  *aRet = scalar;
+  return ScalarResult::Ok;
+}
+
+size_t
+KeyedScalar::SizeOfIncludingThis(mozilla::MallocSizeOf aMallocSizeOf)
+{
+  size_t n = aMallocSizeOf(this);
+  for (auto iter = mScalarKeys.Iter(); !iter.Done(); iter.Next()) {
+    ScalarBase* scalar = static_cast<ScalarBase*>(iter.Data());
+    n += scalar->SizeOfIncludingThis(aMallocSizeOf);
+  }
+  return n;
+}
+
+typedef nsUint32HashKey ScalarIDHashKey;
+typedef nsClassHashtable<ScalarIDHashKey, ScalarBase> ScalarStorageMapType;
+typedef nsClassHashtable<ScalarIDHashKey, KeyedScalar> KeyedScalarStorageMapType;
+
+} // namespace
+
+////////////////////////////////////////////////////////////////////////
+////////////////////////////////////////////////////////////////////////
+//
+// PRIVATE STATE, SHARED BY ALL THREADS
+
+namespace {
+
+// Set to true once this global state has been initialized.
+bool gInitDone = false;
+
+bool gCanRecordBase;
+bool gCanRecordExtended;
+
+// The Name -> ID cache map.
+ScalarMapType gScalarNameIDMap(kScalarCount);
+// The ID -> Scalar Object map. This is a nsClassHashtable, it owns
+// the scalar instance and takes care of deallocating them when they
+// get removed from the map.
+ScalarStorageMapType gScalarStorageMap;
+// The ID -> Keyed Scalar Object map. As for plain scalars, this is
+// nsClassHashtable. See above.
+KeyedScalarStorageMapType gKeyedScalarStorageMap;
+
+} // namespace
+
+////////////////////////////////////////////////////////////////////////
+////////////////////////////////////////////////////////////////////////
+//
+// PRIVATE: Function that may call JS code.
+
+// NOTE: the functions in this section all run without protection from
+// |gTelemetryScalarsMutex|. If they held the mutex, there would be the
+// possibility of deadlock because the JS_ calls that they make may call
+// back into the TelemetryScalar interface, hence trying to re-acquire the mutex.
+//
+// This means that these functions potentially race against threads, but
+// that seems preferable to risking deadlock.
+
+namespace {
+
+/**
+ * Checks if the error should be logged.
+ *
+ * @param aSr The error code.
+ * @return true if the error should be logged, false otherwise.
+ */
+bool
+internal_ShouldLogError(ScalarResult aSr)
+{
+  switch (aSr) {
+    case ScalarResult::StringTooLong: MOZ_FALLTHROUGH;
+    case ScalarResult::KeyTooLong: MOZ_FALLTHROUGH;
+    case ScalarResult::TooManyKeys: MOZ_FALLTHROUGH;
+    case ScalarResult::UnsignedNegativeValue: MOZ_FALLTHROUGH;
+    case ScalarResult::UnsignedTruncatedValue:
+      // Intentional fall-through.
+      return true;
+
+    default:
+      return false;
+  }
+
+  // It should never reach this point.
+  return false;
+}
+
+/**
+ * Converts the error code to a human readable error message and prints it to the
+ * browser console.
+ *
+ * @param aScalarName The name of the scalar that raised the error.
+ * @param aSr The error code.
+ */
+void
+internal_LogScalarError(const nsACString& aScalarName, ScalarResult aSr)
+{
+  nsAutoString errorMessage;
+  AppendUTF8toUTF16(aScalarName, errorMessage);
+
+  switch (aSr) {
+    case ScalarResult::StringTooLong:
+      errorMessage.Append(NS_LITERAL_STRING(" - Truncating scalar value to 50 characters."));
+      break;
+    case ScalarResult::KeyTooLong:
+      errorMessage.Append(NS_LITERAL_STRING(" - The key length must be limited to 70 characters."));
+      break;
+    case ScalarResult::TooManyKeys:
+      errorMessage.Append(NS_LITERAL_STRING(" - Keyed scalars cannot have more than 100 keys."));
+      break;
+    case ScalarResult::UnsignedNegativeValue:
+      errorMessage.Append(NS_LITERAL_STRING(" - Trying to set an unsigned scalar to a negative number."));
+      break;
+    case ScalarResult::UnsignedTruncatedValue:
+      errorMessage.Append(NS_LITERAL_STRING(" - Truncating float/double number."));
+      break;
+    default:
+      // Nothing.
+      return;
+  }
+
+  LogToBrowserConsole(nsIScriptError::warningFlag, errorMessage);
+}
+
+} // namespace
+
+////////////////////////////////////////////////////////////////////////
+////////////////////////////////////////////////////////////////////////
+//
+// PRIVATE: thread-unsafe helpers for the external interface
+
+namespace {
+
+bool
+internal_CanRecordBase()
+{
+  return gCanRecordBase;
+}
+
+bool
+internal_CanRecordExtended()
+{
+  return gCanRecordExtended;
+}
+
+const ScalarInfo&
+internal_InfoForScalarID(mozilla::Telemetry::ScalarID aId)
+{
+  return gScalars[static_cast<uint32_t>(aId)];
+}
+
+/**
+ * Check if the given scalar is a keyed scalar.
+ *
+ * @param aId The scalar enum.
+ * @return true if aId refers to a keyed scalar, false otherwise.
+ */
+bool
+internal_IsKeyedScalar(mozilla::Telemetry::ScalarID aId)
+{
+  return internal_InfoForScalarID(aId).keyed;
+}
+
+bool
+internal_CanRecordForScalarID(mozilla::Telemetry::ScalarID aId)
+{
+  // Get the scalar info from the id.
+  const ScalarInfo &info = internal_InfoForScalarID(aId);
+
+  // Can we record at all?
+  bool canRecordBase = internal_CanRecordBase();
+  if (!canRecordBase) {
+    return false;
+  }
+
+  bool canRecordDataset = CanRecordDataset(info.dataset,
+                                           canRecordBase,
+                                           internal_CanRecordExtended());
+  if (!canRecordDataset) {
+    return false;
+  }
+
+  return true;
+}
+
+/**
+ * Get the scalar enum id from the scalar name.
+ *
+ * @param aName The scalar name.
+ * @param aId The output variable to contain the enum.
+ * @return
+ *   NS_ERROR_FAILURE if this was called before init is completed.
+ *   NS_ERROR_INVALID_ARG if the name can't be found in the scalar definitions.
+ *   NS_OK if the scalar was found and aId contains a valid enum id.
+ */
+nsresult
+internal_GetEnumByScalarName(const nsACString& aName, mozilla::Telemetry::ScalarID* aId)
+{
+  if (!gInitDone) {
+    return NS_ERROR_FAILURE;
+  }
+
+  CharPtrEntryType *entry = gScalarNameIDMap.GetEntry(PromiseFlatCString(aName).get());
+  if (!entry) {
+    return NS_ERROR_INVALID_ARG;
+  }
+  *aId = entry->mData;
+  return NS_OK;
+}
+
+/**
+ * Get a scalar object by its enum id. This implicitly allocates the scalar
+ * object in the storage if it wasn't previously allocated.
+ *
+ * @param aId The scalar id.
+ * @param aRes The output variable that stores scalar object.
+ * @return
+ *   NS_ERROR_INVALID_ARG if the scalar id is unknown.
+ *   NS_ERROR_NOT_AVAILABLE if the scalar is expired.
+ *   NS_OK if the scalar was found. If that's the case, aResult contains a
+ *   valid pointer to a scalar type.
+ */
+nsresult
+internal_GetScalarByEnum(mozilla::Telemetry::ScalarID aId, ScalarBase** aRet)
+{
+  if (!IsValidEnumId(aId)) {
+    MOZ_ASSERT(false, "Requested a scalar with an invalid id.");
+    return NS_ERROR_INVALID_ARG;
+  }
+
+  const uint32_t id = static_cast<uint32_t>(aId);
+
+  ScalarBase* scalar = nullptr;
+  if (gScalarStorageMap.Get(id, &scalar)) {
+    *aRet = scalar;
+    return NS_OK;
+  }
+
+  const ScalarInfo &info = gScalars[id];
+
+  if (IsExpiredVersion(info.expiration())) {
+    return NS_ERROR_NOT_AVAILABLE;
+  }
+
+  scalar = internal_ScalarAllocate(info.kind);
+  if (!scalar) {
+    return NS_ERROR_INVALID_ARG;
+  }
+
+  gScalarStorageMap.Put(id, scalar);
+
+  *aRet = scalar;
+  return NS_OK;
+}
+
+/**
+ * Get a scalar object by its enum id, if we're allowed to record it.
+ *
+ * @param aId The scalar id.
+ * @return The ScalarBase instance or nullptr if we're not allowed to record
+ *         the scalar.
+ */
+ScalarBase*
+internal_GetRecordableScalar(mozilla::Telemetry::ScalarID aId)
+{
+  // Get the scalar by the enum (it also internally checks for aId validity).
+  ScalarBase* scalar = nullptr;
+  nsresult rv = internal_GetScalarByEnum(aId, &scalar);
+  if (NS_FAILED(rv)) {
+    return nullptr;
+  }
+
+  if (internal_IsKeyedScalar(aId)) {
+    return nullptr;
+  }
+
+  // Are we allowed to record this scalar?
+  if (!internal_CanRecordForScalarID(aId)) {
+    return nullptr;
+  }
+
+  return scalar;
+}
+
+} // namespace
+
+
+
+////////////////////////////////////////////////////////////////////////
+////////////////////////////////////////////////////////////////////////
+//
+// PRIVATE: thread-unsafe helpers for the keyed scalars
+
+namespace {
+
+/**
+ * Get a keyed scalar object by its enum id. This implicitly allocates the keyed
+ * scalar object in the storage if it wasn't previously allocated.
+ *
+ * @param aId The scalar id.
+ * @param aRes The output variable that stores scalar object.
+ * @return
+ *   NS_ERROR_INVALID_ARG if the scalar id is unknown or a this is a keyed string
+ *                        scalar.
+ *   NS_ERROR_NOT_AVAILABLE if the scalar is expired.
+ *   NS_OK if the scalar was found. If that's the case, aResult contains a
+ *   valid pointer to a scalar type.
+ */
+nsresult
+internal_GetKeyedScalarByEnum(mozilla::Telemetry::ScalarID aId, KeyedScalar** aRet)
+{
+  if (!IsValidEnumId(aId)) {
+    MOZ_ASSERT(false, "Requested a keyed scalar with an invalid id.");
+    return NS_ERROR_INVALID_ARG;
+  }
+
+  const uint32_t id = static_cast<uint32_t>(aId);
+
+  KeyedScalar* scalar = nullptr;
+  if (gKeyedScalarStorageMap.Get(id, &scalar)) {
+    *aRet = scalar;
+    return NS_OK;
+  }
+
+  const ScalarInfo &info = gScalars[id];
+
+  if (IsExpiredVersion(info.expiration())) {
+    return NS_ERROR_NOT_AVAILABLE;
+  }
+
+  // We don't currently support keyed string scalars. Disable them.
+  if (info.kind == nsITelemetry::SCALAR_STRING) {
+    MOZ_ASSERT(false, "Keyed string scalars are not currently supported.");
+    return NS_ERROR_INVALID_ARG;
+  }
+
+  scalar = new KeyedScalar(info.kind);
+  if (!scalar) {
+    return NS_ERROR_INVALID_ARG;
+  }
+
+  gKeyedScalarStorageMap.Put(id, scalar);
+
+  *aRet = scalar;
+  return NS_OK;
+}
+
+/**
+ * Get a keyed scalar object by its enum id, if we're allowed to record it.
+ *
+ * @param aId The scalar id.
+ * @return The KeyedScalar instance or nullptr if we're not allowed to record
+ *         the scalar.
+ */
+KeyedScalar*
+internal_GetRecordableKeyedScalar(mozilla::Telemetry::ScalarID aId)
+{
+  // Get the scalar by the enum (it also internally checks for aId validity).
+  KeyedScalar* scalar = nullptr;
+  nsresult rv = internal_GetKeyedScalarByEnum(aId, &scalar);
+  if (NS_FAILED(rv)) {
+    return nullptr;
+  }
+
+  if (!internal_IsKeyedScalar(aId)) {
+    return nullptr;
+  }
+
+  // Are we allowed to record this scalar?
+  if (!internal_CanRecordForScalarID(aId)) {
+    return nullptr;
+  }
+
+  return scalar;
+}
+
+} // namespace
+
+////////////////////////////////////////////////////////////////////////
+////////////////////////////////////////////////////////////////////////
+//
+// EXTERNALLY VISIBLE FUNCTIONS in namespace TelemetryScalars::
+
+// This is a StaticMutex rather than a plain Mutex (1) so that
+// it gets initialised in a thread-safe manner the first time
+// it is used, and (2) because it is never de-initialised, and
+// a normal Mutex would show up as a leak in BloatView.  StaticMutex
+// also has the "OffTheBooks" property, so it won't show as a leak
+// in BloatView.
+// Another reason to use a StaticMutex instead of a plain Mutex is
+// that, due to the nature of Telemetry, we cannot rely on having a
+// mutex initialized in InitializeGlobalState. Unfortunately, we
+// cannot make sure that no other function is called before this point.
+static StaticMutex gTelemetryScalarsMutex;
+
+void
+TelemetryScalar::InitializeGlobalState(bool aCanRecordBase, bool aCanRecordExtended)
+{
+  StaticMutexAutoLock locker(gTelemetryScalarsMutex);
+  MOZ_ASSERT(!gInitDone, "TelemetryScalar::InitializeGlobalState "
+             "may only be called once");
+
+  gCanRecordBase = aCanRecordBase;
+  gCanRecordExtended = aCanRecordExtended;
+
+  // Populate the static scalar name->id cache. Note that the scalar names are
+  // statically allocated and come from the automatically generated TelemetryScalarData.h.
+  uint32_t scalarCount = static_cast<uint32_t>(mozilla::Telemetry::ScalarID::ScalarCount);
+  for (uint32_t i = 0; i < scalarCount; i++) {
+    CharPtrEntryType *entry = gScalarNameIDMap.PutEntry(gScalars[i].name());
+    entry->mData = static_cast<mozilla::Telemetry::ScalarID>(i);
+  }
+
+#ifdef DEBUG
+  gScalarNameIDMap.MarkImmutable();
+#endif
+  gInitDone = true;
+}
+
+void
+TelemetryScalar::DeInitializeGlobalState()
+{
+  StaticMutexAutoLock locker(gTelemetryScalarsMutex);
+  gCanRecordBase = false;
+  gCanRecordExtended = false;
+  gScalarNameIDMap.Clear();
+  gScalarStorageMap.Clear();
+  gKeyedScalarStorageMap.Clear();
+  gInitDone = false;
+}
+
+void
+TelemetryScalar::SetCanRecordBase(bool b)
+{
+  StaticMutexAutoLock locker(gTelemetryScalarsMutex);
+  gCanRecordBase = b;
+}
+
+void
+TelemetryScalar::SetCanRecordExtended(bool b) {
+  StaticMutexAutoLock locker(gTelemetryScalarsMutex);
+  gCanRecordExtended = b;
+}
+
+/**
+ * Adds the value to the given scalar.
+ *
+ * @param aName The scalar name.
+ * @param aVal The numeric value to add to the scalar.
+ * @param aCx The JS context.
+ * @return NS_OK if the value was added or if we're not allowed to record to this
+ *  dataset. Otherwise, return an error.
+ */
+nsresult
+TelemetryScalar::Add(const nsACString& aName, JS::HandleValue aVal, JSContext* aCx)
+{
+  // Unpack the aVal to nsIVariant. This uses the JS context.
+  nsCOMPtr<nsIVariant> unpackedVal;
+  nsresult rv =
+    nsContentUtils::XPConnect()->JSToVariant(aCx, aVal,  getter_AddRefs(unpackedVal));
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  ScalarResult sr;
+  {
+    StaticMutexAutoLock locker(gTelemetryScalarsMutex);
+
+    mozilla::Telemetry::ScalarID id;
+    rv = internal_GetEnumByScalarName(aName, &id);
+    if (NS_FAILED(rv)) {
+      return rv;
+    }
+
+    // We're trying to set a plain scalar, so make sure this is one.
+    if (internal_IsKeyedScalar(id)) {
+      return NS_ERROR_ILLEGAL_VALUE;
+    }
+
+    // Are we allowed to record this scalar?
+    if (!internal_CanRecordForScalarID(id)) {
+      return NS_OK;
+    }
+
+    // Finally get the scalar.
+    ScalarBase* scalar = nullptr;
+    rv = internal_GetScalarByEnum(id, &scalar);
+    if (NS_FAILED(rv)) {
+      // Don't throw on expired scalars.
+      if (rv == NS_ERROR_NOT_AVAILABLE) {
+        return NS_OK;
+      }
+      return rv;
+    }
+
+    sr = scalar->AddValue(unpackedVal);
+  }
+
+  // Warn the user about the error if we need to.
+  if (internal_ShouldLogError(sr)) {
+    internal_LogScalarError(aName, sr);
+  }
+
+  return MapToNsResult(sr);
+}
+
+/**
+ * Adds the value to the given scalar.
+ *
+ * @param aName The scalar name.
+ * @param aKey The key name.
+ * @param aVal The numeric value to add to the scalar.
+ * @param aCx The JS context.
+ * @return NS_OK if the value was added or if we're not allow to record to this
+ *  dataset. Otherwise, return an error.
+ */
+nsresult
+TelemetryScalar::Add(const nsACString& aName, const nsAString& aKey, JS::HandleValue aVal,
+                     JSContext* aCx)
+{
+  // Unpack the aVal to nsIVariant. This uses the JS context.
+  nsCOMPtr<nsIVariant> unpackedVal;
+  nsresult rv =
+    nsContentUtils::XPConnect()->JSToVariant(aCx, aVal,  getter_AddRefs(unpackedVal));
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  ScalarResult sr;
+  {
+    StaticMutexAutoLock locker(gTelemetryScalarsMutex);
+
+    mozilla::Telemetry::ScalarID id;
+    rv = internal_GetEnumByScalarName(aName, &id);
+    if (NS_FAILED(rv)) {
+      return rv;
+    }
+
+    // Make sure this is a keyed scalar.
+    if (!internal_IsKeyedScalar(id)) {
+      return NS_ERROR_ILLEGAL_VALUE;
+    }
+
+    // Are we allowed to record this scalar?
+    if (!internal_CanRecordForScalarID(id)) {
+      return NS_OK;
+    }
+
+    // Finally get the scalar.
+    KeyedScalar* scalar = nullptr;
+    rv = internal_GetKeyedScalarByEnum(id, &scalar);
+    if (NS_FAILED(rv)) {
+      // Don't throw on expired scalars.
+      if (rv == NS_ERROR_NOT_AVAILABLE) {
+        return NS_OK;
+      }
+      return rv;
+    }
+
+    sr = scalar->AddValue(aKey, unpackedVal);
+  }
+
+  // Warn the user about the error if we need to.
+  if (internal_ShouldLogError(sr)) {
+    internal_LogScalarError(aName, sr);
+  }
+
+  return MapToNsResult(sr);
+}
+
+/**
+ * Adds the value to the given scalar.
+ *
+ * @param aId The scalar enum id.
+ * @param aVal The numeric value to add to the scalar.
+ */
+void
+TelemetryScalar::Add(mozilla::Telemetry::ScalarID aId, uint32_t aValue)
+{
+  StaticMutexAutoLock locker(gTelemetryScalarsMutex);
+
+  ScalarBase* scalar = internal_GetRecordableScalar(aId);
+  if (!scalar) {
+    return;
+  }
+
+  scalar->AddValue(aValue);
+}
+
+/**
+ * Adds the value to the given keyed scalar.
+ *
+ * @param aId The scalar enum id.
+ * @param aKey The key name.
+ * @param aVal The numeric value to add to the scalar.
+ */
+void
+TelemetryScalar::Add(mozilla::Telemetry::ScalarID aId, const nsAString& aKey,
+                     uint32_t aValue)
+{
+  StaticMutexAutoLock locker(gTelemetryScalarsMutex);
+
+  KeyedScalar* scalar = internal_GetRecordableKeyedScalar(aId);
+  if (!scalar) {
+    return;
+  }
+
+  scalar->AddValue(aKey, aValue);
+}
+
+/**
+ * Sets the scalar to the given value.
+ *
+ * @param aName The scalar name.
+ * @param aVal The value to set the scalar to.
+ * @param aCx The JS context.
+ * @return NS_OK if the value was added or if we're not allow to record to this
+ *  dataset. Otherwise, return an error.
+ */
+nsresult
+TelemetryScalar::Set(const nsACString& aName, JS::HandleValue aVal, JSContext* aCx)
+{
+  // Unpack the aVal to nsIVariant. This uses the JS context.
+  nsCOMPtr<nsIVariant> unpackedVal;
+  nsresult rv =
+    nsContentUtils::XPConnect()->JSToVariant(aCx, aVal,  getter_AddRefs(unpackedVal));
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  ScalarResult sr;
+  {
+    StaticMutexAutoLock locker(gTelemetryScalarsMutex);
+
+    mozilla::Telemetry::ScalarID id;
+    rv = internal_GetEnumByScalarName(aName, &id);
+    if (NS_FAILED(rv)) {
+      return rv;
+    }
+
+    // We're trying to set a plain scalar, so make sure this is one.
+    if (internal_IsKeyedScalar(id)) {
+      return NS_ERROR_ILLEGAL_VALUE;
+    }
+
+    // Are we allowed to record this scalar?
+    if (!internal_CanRecordForScalarID(id)) {
+      return NS_OK;
+    }
+
+    // Finally get the scalar.
+    ScalarBase* scalar = nullptr;
+    rv = internal_GetScalarByEnum(id, &scalar);
+    if (NS_FAILED(rv)) {
+      // Don't throw on expired scalars.
+      if (rv == NS_ERROR_NOT_AVAILABLE) {
+        return NS_OK;
+      }
+      return rv;
+    }
+
+    sr = scalar->SetValue(unpackedVal);
+  }
+
+  // Warn the user about the error if we need to.
+  if (internal_ShouldLogError(sr)) {
+    internal_LogScalarError(aName, sr);
+  }
+
+  return MapToNsResult(sr);
+}
+
+/**
+ * Sets the keyed scalar to the given value.
+ *
+ * @param aName The scalar name.
+ * @param aKey The key name.
+ * @param aVal The value to set the scalar to.
+ * @param aCx The JS context.
+ * @return NS_OK if the value was added or if we're not allow to record to this
+ *  dataset. Otherwise, return an error.
+ */
+nsresult
+TelemetryScalar::Set(const nsACString& aName, const nsAString& aKey, JS::HandleValue aVal,
+                     JSContext* aCx)
+{
+  // Unpack the aVal to nsIVariant. This uses the JS context.
+  nsCOMPtr<nsIVariant> unpackedVal;
+  nsresult rv =
+    nsContentUtils::XPConnect()->JSToVariant(aCx, aVal,  getter_AddRefs(unpackedVal));
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  ScalarResult sr;
+  {
+    StaticMutexAutoLock locker(gTelemetryScalarsMutex);
+
+    mozilla::Telemetry::ScalarID id;
+    rv = internal_GetEnumByScalarName(aName, &id);
+    if (NS_FAILED(rv)) {
+      return rv;
+    }
+
+    // We're trying to set a keyed scalar. Report an error if this isn't one.
+    if (!internal_IsKeyedScalar(id)) {
+      return NS_ERROR_ILLEGAL_VALUE;
+    }
+
+    // Are we allowed to record this scalar?
+    if (!internal_CanRecordForScalarID(id)) {
+      return NS_OK;
+    }
+
+    // Finally get the scalar.
+    KeyedScalar* scalar = nullptr;
+    rv = internal_GetKeyedScalarByEnum(id, &scalar);
+    if (NS_FAILED(rv)) {
+      // Don't throw on expired scalars.
+      if (rv == NS_ERROR_NOT_AVAILABLE) {
+        return NS_OK;
+      }
+      return rv;
+    }
+
+    sr = scalar->SetValue(aKey, unpackedVal);
+  }
+
+  // Warn the user about the error if we need to.
+  if (internal_ShouldLogError(sr)) {
+    internal_LogScalarError(aName, sr);
+  }
+
+  return MapToNsResult(sr);
+}
+
+/**
+ * Sets the scalar to the given numeric value.
+ *
+ * @param aId The scalar enum id.
+ * @param aValue The numeric, unsigned value to set the scalar to.
+ */
+void
+TelemetryScalar::Set(mozilla::Telemetry::ScalarID aId, uint32_t aValue)
+{
+  StaticMutexAutoLock locker(gTelemetryScalarsMutex);
+
+  ScalarBase* scalar = internal_GetRecordableScalar(aId);
+  if (!scalar) {
+    return;
+  }
+
+  scalar->SetValue(aValue);
+}
+
+/**
+ * Sets the scalar to the given string value.
+ *
+ * @param aId The scalar enum id.
+ * @param aValue The string value to set the scalar to.
+ */
+void
+TelemetryScalar::Set(mozilla::Telemetry::ScalarID aId, const nsAString& aValue)
+{
+  StaticMutexAutoLock locker(gTelemetryScalarsMutex);
+
+  ScalarBase* scalar = internal_GetRecordableScalar(aId);
+  if (!scalar) {
+    return;
+  }
+
+  scalar->SetValue(aValue);
+}
+
+/**
+ * Sets the scalar to the given boolean value.
+ *
+ * @param aId The scalar enum id.
+ * @param aValue The boolean value to set the scalar to.
+ */
+void
+TelemetryScalar::Set(mozilla::Telemetry::ScalarID aId, bool aValue)
+{
+  StaticMutexAutoLock locker(gTelemetryScalarsMutex);
+
+  ScalarBase* scalar = internal_GetRecordableScalar(aId);
+  if (!scalar) {
+    return;
+  }
+
+  scalar->SetValue(aValue);
+}
+
+/**
+ * Sets the keyed scalar to the given numeric value.
+ *
+ * @param aId The scalar enum id.
+ * @param aKey The scalar key.
+ * @param aValue The numeric, unsigned value to set the scalar to.
+ */
+void
+TelemetryScalar::Set(mozilla::Telemetry::ScalarID aId, const nsAString& aKey,
+                     uint32_t aValue)
+{
+  StaticMutexAutoLock locker(gTelemetryScalarsMutex);
+
+  KeyedScalar* scalar = internal_GetRecordableKeyedScalar(aId);
+  if (!scalar) {
+    return;
+  }
+
+  scalar->SetValue(aKey, aValue);
+}
+
+/**
+ * Sets the scalar to the given boolean value.
+ *
+ * @param aId The scalar enum id.
+ * @param aKey The scalar key.
+ * @param aValue The boolean value to set the scalar to.
+ */
+void
+TelemetryScalar::Set(mozilla::Telemetry::ScalarID aId, const nsAString& aKey,
+                     bool aValue)
+{
+  StaticMutexAutoLock locker(gTelemetryScalarsMutex);
+
+  KeyedScalar* scalar = internal_GetRecordableKeyedScalar(aId);
+  if (!scalar) {
+    return;
+  }
+
+  scalar->SetValue(aKey, aValue);
+}
+
+/**
+ * Sets the scalar to the maximum of the current and the passed value.
+ *
+ * @param aName The scalar name.
+ * @param aVal The numeric value to set the scalar to.
+ * @param aCx The JS context.
+ * @return NS_OK if the value was added or if we're not allow to record to this
+ *  dataset. Otherwise, return an error.
+ */
+nsresult
+TelemetryScalar::SetMaximum(const nsACString& aName, JS::HandleValue aVal, JSContext* aCx)
+{
+  // Unpack the aVal to nsIVariant. This uses the JS context.
+  nsCOMPtr<nsIVariant> unpackedVal;
+  nsresult rv =
+    nsContentUtils::XPConnect()->JSToVariant(aCx, aVal,  getter_AddRefs(unpackedVal));
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  ScalarResult sr;
+  {
+    StaticMutexAutoLock locker(gTelemetryScalarsMutex);
+
+    mozilla::Telemetry::ScalarID id;
+    rv = internal_GetEnumByScalarName(aName, &id);
+    if (NS_FAILED(rv)) {
+      return rv;
+    }
+
+    // Make sure this is not a keyed scalar.
+    if (internal_IsKeyedScalar(id)) {
+      return NS_ERROR_ILLEGAL_VALUE;
+    }
+
+    // Are we allowed to record this scalar?
+    if (!internal_CanRecordForScalarID(id)) {
+      return NS_OK;
+    }
+
+    // Finally get the scalar.
+    ScalarBase* scalar = nullptr;
+    rv = internal_GetScalarByEnum(id, &scalar);
+    if (NS_FAILED(rv)) {
+      // Don't throw on expired scalars.
+      if (rv == NS_ERROR_NOT_AVAILABLE) {
+        return NS_OK;
+      }
+      return rv;
+    }
+
+    sr = scalar->SetMaximum(unpackedVal);
+  }
+
+  // Warn the user about the error if we need to.
+  if (internal_ShouldLogError(sr)) {
+    internal_LogScalarError(aName, sr);
+  }
+
+  return MapToNsResult(sr);
+}
+
+/**
+ * Sets the scalar to the maximum of the current and the passed value.
+ *
+ * @param aName The scalar name.
+ * @param aKey The key name.
+ * @param aVal The numeric value to set the scalar to.
+ * @param aCx The JS context.
+ * @return NS_OK if the value was added or if we're not allow to record to this
+ *  dataset. Otherwise, return an error.
+ */
+nsresult
+TelemetryScalar::SetMaximum(const nsACString& aName, const nsAString& aKey, JS::HandleValue aVal,
+                            JSContext* aCx)
+{
+  // Unpack the aVal to nsIVariant. This uses the JS context.
+  nsCOMPtr<nsIVariant> unpackedVal;
+  nsresult rv =
+    nsContentUtils::XPConnect()->JSToVariant(aCx, aVal,  getter_AddRefs(unpackedVal));
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  ScalarResult sr;
+  {
+    StaticMutexAutoLock locker(gTelemetryScalarsMutex);
+
+    mozilla::Telemetry::ScalarID id;
+    rv = internal_GetEnumByScalarName(aName, &id);
+    if (NS_FAILED(rv)) {
+      return rv;
+    }
+
+    // Make sure this is a keyed scalar.
+    if (!internal_IsKeyedScalar(id)) {
+      return NS_ERROR_ILLEGAL_VALUE;
+    }
+
+    // Are we allowed to record this scalar?
+    if (!internal_CanRecordForScalarID(id)) {
+      return NS_OK;
+    }
+
+    // Finally get the scalar.
+    KeyedScalar* scalar = nullptr;
+    rv = internal_GetKeyedScalarByEnum(id, &scalar);
+    if (NS_FAILED(rv)) {
+      // Don't throw on expired scalars.
+      if (rv == NS_ERROR_NOT_AVAILABLE) {
+        return NS_OK;
+      }
+      return rv;
+    }
+
+    sr = scalar->SetMaximum(aKey, unpackedVal);
+  }
+
+  // Warn the user about the error if we need to.
+  if (internal_ShouldLogError(sr)) {
+    internal_LogScalarError(aName, sr);
+  }
+
+  return MapToNsResult(sr);
+}
+
+/**
+ * Sets the scalar to the maximum of the current and the passed value.
+ *
+ * @param aId The scalar enum id.
+ * @param aValue The numeric value to set the scalar to.
+ */
+void
+TelemetryScalar::SetMaximum(mozilla::Telemetry::ScalarID aId, uint32_t aValue)
+{
+  StaticMutexAutoLock locker(gTelemetryScalarsMutex);
+
+  ScalarBase* scalar = internal_GetRecordableScalar(aId);
+  if (!scalar) {
+    return;
+  }
+
+  scalar->SetMaximum(aValue);
+}
+
+/**
+ * Sets the keyed scalar to the maximum of the current and the passed value.
+ *
+ * @param aId The scalar enum id.
+ * @param aKey The key name.
+ * @param aValue The numeric value to set the scalar to.
+ */
+void
+TelemetryScalar::SetMaximum(mozilla::Telemetry::ScalarID aId, const nsAString& aKey,
+                            uint32_t aValue)
+{
+  StaticMutexAutoLock locker(gTelemetryScalarsMutex);
+
+  KeyedScalar* scalar = internal_GetRecordableKeyedScalar(aId);
+  if (!scalar) {
+    return;
+  }
+
+  scalar->SetMaximum(aKey, aValue);
+}
+
+/**
+ * Serializes the scalars from the given dataset to a json-style object and resets them.
+ * The returned structure looks like {"group1.probe":1,"group1.other_probe":false,...}.
+ *
+ * @param aDataset DATASET_RELEASE_CHANNEL_OPTOUT or DATASET_RELEASE_CHANNEL_OPTIN.
+ * @param aClear Whether to clear out the scalars after snapshotting.
+ */
+nsresult
+TelemetryScalar::CreateSnapshots(unsigned int aDataset, bool aClearScalars, JSContext* aCx,
+                                 uint8_t optional_argc, JS::MutableHandle<JS::Value> aResult)
+{
+  // If no arguments were passed in, apply the default value.
+  if (!optional_argc) {
+    aClearScalars = false;
+  }
+
+  JS::Rooted<JSObject*> root_obj(aCx, JS_NewPlainObject(aCx));
+  if (!root_obj) {
+    return NS_ERROR_FAILURE;
+  }
+  aResult.setObject(*root_obj);
+
+  // Only lock the mutex while accessing our data, without locking any JS related code.
+  typedef mozilla::Pair<const char*, nsCOMPtr<nsIVariant>> DataPair;
+  nsTArray<DataPair> scalarsToReflect;
+  {
+    StaticMutexAutoLock locker(gTelemetryScalarsMutex);
+    // Iterate the scalars in gScalarStorageMap. The storage may contain empty or yet to be
+    // initialized scalars.
+    for (auto iter = gScalarStorageMap.Iter(); !iter.Done(); iter.Next()) {
+      ScalarBase* scalar = static_cast<ScalarBase*>(iter.Data());
+
+      // Get the informations for this scalar.
+      const ScalarInfo& info = gScalars[iter.Key()];
+
+      // Serialize the scalar if it's in the desired dataset.
+      if (IsInDataset(info.dataset, aDataset)) {
+        // Get the scalar value.
+        nsCOMPtr<nsIVariant> scalarValue;
+        nsresult rv = scalar->GetValue(scalarValue);
+        if (NS_FAILED(rv)) {
+          return rv;
+        }
+        // Append it to our list.
+        scalarsToReflect.AppendElement(mozilla::MakePair(info.name(), scalarValue));
+      }
+    }
+
+    if (aClearScalars) {
+      // The map already takes care of freeing the allocated memory.
+      gScalarStorageMap.Clear();
+    }
+  }
+
+  // Reflect it to JS.
+  for (nsTArray<DataPair>::size_type i = 0; i < scalarsToReflect.Length(); i++) {
+    const DataPair& scalar = scalarsToReflect[i];
+
+    // Convert it to a JS Val.
+    JS::Rooted<JS::Value> scalarJsValue(aCx);
+    nsresult rv =
+      nsContentUtils::XPConnect()->VariantToJS(aCx, root_obj, scalar.second(), &scalarJsValue);
+    if (NS_FAILED(rv)) {
+      return rv;
+    }
+
+    // Add it to the scalar object.
+    if (!JS_DefineProperty(aCx, root_obj, scalar.first(), scalarJsValue, JSPROP_ENUMERATE)) {
+      return NS_ERROR_FAILURE;
+    }
+  }
+
+  return NS_OK;
+}
+
+/**
+ * Serializes the scalars from the given dataset to a json-style object and resets them.
+ * The returned structure looks like:
+ *   { "group1.probe": { "key_1": 2, "key_2": 1, ... }, ... }
+ *
+ * @param aDataset DATASET_RELEASE_CHANNEL_OPTOUT or DATASET_RELEASE_CHANNEL_OPTIN.
+ * @param aClear Whether to clear out the keyed scalars after snapshotting.
+ */
+nsresult
+TelemetryScalar::CreateKeyedSnapshots(unsigned int aDataset, bool aClearScalars, JSContext* aCx,
+                                      uint8_t optional_argc, JS::MutableHandle<JS::Value> aResult)
+{
+  // If no arguments were passed in, apply the default value.
+  if (!optional_argc) {
+    aClearScalars = false;
+  }
+
+  JS::Rooted<JSObject*> root_obj(aCx, JS_NewPlainObject(aCx));
+  if (!root_obj) {
+    return NS_ERROR_FAILURE;
+  }
+  aResult.setObject(*root_obj);
+
+  // Only lock the mutex while accessing our data, without locking any JS related code.
+  typedef mozilla::Pair<const char*, nsTArray<KeyedScalar::KeyValuePair>> DataPair;
+  nsTArray<DataPair> scalarsToReflect;
+  {
+    StaticMutexAutoLock locker(gTelemetryScalarsMutex);
+    // Iterate the scalars in gKeyedScalarStorageMap. The storage may contain empty or yet
+    // to be initialized scalars.
+    for (auto iter = gKeyedScalarStorageMap.Iter(); !iter.Done(); iter.Next()) {
+      KeyedScalar* scalar = static_cast<KeyedScalar*>(iter.Data());
+
+      // Get the informations for this scalar.
+      const ScalarInfo& info = gScalars[iter.Key()];
+
+      // Serialize the scalar if it's in the desired dataset.
+      if (IsInDataset(info.dataset, aDataset)) {
+        // Get the keys for this scalar.
+        nsTArray<KeyedScalar::KeyValuePair> scalarKeyedData;
+        nsresult rv = scalar->GetValue(scalarKeyedData);
+        if (NS_FAILED(rv)) {
+          return rv;
+        }
+        // Append it to our list.
+        scalarsToReflect.AppendElement(mozilla::MakePair(info.name(), scalarKeyedData));
+      }
+    }
+
+    if (aClearScalars) {
+      // The map already takes care of freeing the allocated memory.
+      gKeyedScalarStorageMap.Clear();
+    }
+  }
+
+  // Reflect it to JS.
+  for (nsTArray<DataPair>::size_type i = 0; i < scalarsToReflect.Length(); i++) {
+    const DataPair& keyedScalarData = scalarsToReflect[i];
+
+    // Go through each keyed scalar and create a keyed scalar object.
+    // This object will hold the values for all the keyed scalar keys.
+    JS::RootedObject keyedScalarObj(aCx, JS_NewPlainObject(aCx));
+
+    // Define a property for each scalar key, then add it to the keyed scalar
+    // object.
+    const nsTArray<KeyedScalar::KeyValuePair>& keyProps = keyedScalarData.second();
+    for (uint32_t i = 0; i < keyProps.Length(); i++) {
+      const KeyedScalar::KeyValuePair& keyData = keyProps[i];
+
+      // Convert the value for the key to a JSValue.
+      JS::Rooted<JS::Value> keyJsValue(aCx);
+      nsresult rv =
+        nsContentUtils::XPConnect()->VariantToJS(aCx, keyedScalarObj, keyData.second(), &keyJsValue);
+      if (NS_FAILED(rv)) {
+        return rv;
+      }
+
+      // Add the key to the scalar representation.
+      const NS_ConvertUTF8toUTF16 key(keyData.first());
+      if (!JS_DefineUCProperty(aCx, keyedScalarObj, key.Data(), key.Length(), keyJsValue, JSPROP_ENUMERATE)) {
+        return NS_ERROR_FAILURE;
+      }
+    }
+
+    // Add the scalar to the root object.
+    if (!JS_DefineProperty(aCx, root_obj, keyedScalarData.first(), keyedScalarObj, JSPROP_ENUMERATE)) {
+      return NS_ERROR_FAILURE;
+    }
+  }
+
+  return NS_OK;
+}
+
+/**
+ * Resets all the stored scalars. This is intended to be only used in tests.
+ */
+void
+TelemetryScalar::ClearScalars()
+{
+  StaticMutexAutoLock locker(gTelemetryScalarsMutex);
+  gScalarStorageMap.Clear();
+  gKeyedScalarStorageMap.Clear();
+}
+
+size_t
+TelemetryScalar::GetMapShallowSizesOfExcludingThis(mozilla::MallocSizeOf aMallocSizeOf)
+{
+  StaticMutexAutoLock locker(gTelemetryScalarsMutex);
+  return gScalarNameIDMap.ShallowSizeOfExcludingThis(aMallocSizeOf);
+}
+
+size_t
+TelemetryScalar::GetScalarSizesOfIncludingThis(mozilla::MallocSizeOf aMallocSizeOf)
+{
+  StaticMutexAutoLock locker(gTelemetryScalarsMutex);
+  size_t n = 0;
+  // For the plain scalars...
+  for (auto iter = gScalarStorageMap.Iter(); !iter.Done(); iter.Next()) {
+    ScalarBase* scalar = static_cast<ScalarBase*>(iter.Data());
+    n += scalar->SizeOfIncludingThis(aMallocSizeOf);
+  }
+  // ...and for the keyed scalars.
+  for (auto iter = gKeyedScalarStorageMap.Iter(); !iter.Done(); iter.Next()) {
+    KeyedScalar* scalar = static_cast<KeyedScalar*>(iter.Data());
+    n += scalar->SizeOfIncludingThis(aMallocSizeOf);
+  }
+  return n;
+}