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/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=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 "MsaaIdGenerator.h"
#include "mozilla/a11y/AccessibleWrap.h"
#include "mozilla/ClearOnShutdown.h"
#include "mozilla/dom/ContentChild.h"
#include "mozilla/StaticPtr.h"
#include "mozilla/Unused.h"
#include "nsDataHashtable.h"
#include "nsIXULRuntime.h"
// These constants may be adjusted to modify the proportion of the Child ID
// allocated to the content ID vs proportion allocated to the unique ID. They
// must always sum to 31, ie. the width of a 32-bit integer less the sign bit.
// NB: kNumContentProcessIDBits must be large enough to successfully hold the
// maximum permitted number of e10s content processes. If the e10s maximum
// number of content processes changes, then kNumContentProcessIDBits must also
// be updated if necessary to accommodate that new value!
static const uint32_t kNumContentProcessIDBits = 7UL;
static const uint32_t kNumUniqueIDBits = (31UL - kNumContentProcessIDBits);
static_assert(kNumContentProcessIDBits + kNumUniqueIDBits == 31,
"Allocation of Content ID bits and Unique ID bits must sum to 31");
namespace mozilla {
namespace a11y {
namespace detail {
typedef nsDataHashtable<nsUint64HashKey, uint32_t> ContentParentIdMap;
#pragma pack(push, 1)
union MsaaID
{
int32_t mInt32;
uint32_t mUInt32;
struct
{
uint32_t mUniqueID:kNumUniqueIDBits;
uint32_t mContentProcessID:kNumContentProcessIDBits;
uint32_t mSignBit:1;
}
mCracked;
};
#pragma pack(pop)
static uint32_t
BuildMsaaID(const uint32_t aID, const uint32_t aContentProcessID)
{
MsaaID id;
id.mCracked.mSignBit = 0;
id.mCracked.mUniqueID = aID;
id.mCracked.mContentProcessID = aContentProcessID;
return ~id.mUInt32;
}
class MsaaIDCracker
{
public:
explicit MsaaIDCracker(const uint32_t aMsaaID)
{
mID.mUInt32 = ~aMsaaID;
}
uint32_t GetContentProcessId()
{
return mID.mCracked.mContentProcessID;
}
uint32_t GetUniqueId()
{
return mID.mCracked.mUniqueID;
}
private:
MsaaID mID;
};
} // namespace detail
constexpr MsaaIdGenerator::MsaaIdGenerator()
: mIDSet(kNumUniqueIDBits)
{}
uint32_t
MsaaIdGenerator::GetID()
{
uint32_t id = mIDSet.GetID();
MOZ_ASSERT(id <= ((1UL << kNumUniqueIDBits) - 1UL));
return detail::BuildMsaaID(id, ResolveContentProcessID());
}
void
MsaaIdGenerator::ReleaseID(AccessibleWrap* aAccWrap)
{
MOZ_ASSERT(aAccWrap);
uint32_t id = aAccWrap->GetExistingID();
MOZ_ASSERT(id != AccessibleWrap::kNoID);
detail::MsaaIDCracker cracked(id);
if (cracked.GetContentProcessId() != ResolveContentProcessID()) {
// This may happen if chrome holds a proxy whose ID was originally generated
// by a content process. Since ReleaseID only has meaning in the process
// that originally generated that ID, we ignore ReleaseID calls for any ID
// that did not come from the current process.
MOZ_ASSERT(aAccWrap->IsProxy());
return;
}
mIDSet.ReleaseID(cracked.GetUniqueId());
}
bool
MsaaIdGenerator::IsChromeID(uint32_t aID)
{
detail::MsaaIDCracker cracked(aID);
return cracked.GetContentProcessId() == 0;
}
bool
MsaaIdGenerator::IsIDForThisContentProcess(uint32_t aID)
{
MOZ_ASSERT(XRE_IsContentProcess());
detail::MsaaIDCracker cracked(aID);
return cracked.GetContentProcessId() == ResolveContentProcessID();
}
bool
MsaaIdGenerator::IsIDForContentProcess(uint32_t aID,
dom::ContentParentId aIPCContentProcessId)
{
MOZ_ASSERT(XRE_IsParentProcess());
detail::MsaaIDCracker cracked(aID);
return cracked.GetContentProcessId() ==
GetContentProcessIDFor(aIPCContentProcessId);
}
bool
MsaaIdGenerator::IsSameContentProcessFor(uint32_t aFirstID, uint32_t aSecondID)
{
detail::MsaaIDCracker firstCracked(aFirstID);
detail::MsaaIDCracker secondCracked(aSecondID);
return firstCracked.GetContentProcessId() ==
secondCracked.GetContentProcessId();
}
uint32_t
MsaaIdGenerator::ResolveContentProcessID()
{
if (XRE_IsParentProcess()) {
return 0;
}
dom::ContentChild* contentChild = dom::ContentChild::GetSingleton();
uint32_t result = contentChild->GetMsaaID();
MOZ_ASSERT(result);
return result;
}
/**
* Each dom::ContentParent has a 64-bit ID. This ID is monotonically increasing
* with each new content process, so those IDs are effectively single-use. OTOH,
* MSAA requires 32-bit IDs. Since we only allocate kNumContentProcessIDBits for
* the content process ID component, the MSAA content process ID value must be
* reusable. sContentParentIdMap holds the current associations between
* dom::ContentParent IDs and the MSAA content parent IDs that have been
* allocated to them.
*/
static StaticAutoPtr<detail::ContentParentIdMap> sContentParentIdMap;
static const uint32_t kBitsPerByte = 8UL;
// Set sContentProcessIdBitmap[0] to 1 to reserve the Chrome process's id
static uint64_t sContentProcessIdBitmap[(1UL << kNumContentProcessIDBits) /
(sizeof(uint64_t) * kBitsPerByte)] = {1ULL};
static const uint32_t kBitsPerElement = sizeof(sContentProcessIdBitmap[0]) *
kBitsPerByte;
uint32_t
MsaaIdGenerator::GetContentProcessIDFor(dom::ContentParentId aIPCContentProcessID)
{
MOZ_ASSERT(XRE_IsParentProcess() && NS_IsMainThread());
if (!sContentParentIdMap) {
sContentParentIdMap = new detail::ContentParentIdMap();
ClearOnShutdown(&sContentParentIdMap);
}
uint32_t value = 0;
if (sContentParentIdMap->Get(aIPCContentProcessID, &value)) {
return value;
}
uint32_t index = 0;
for (; index < ArrayLength(sContentProcessIdBitmap); ++index) {
if (sContentProcessIdBitmap[index] == UINT64_MAX) {
continue;
}
uint32_t bitIndex = CountTrailingZeroes64(~sContentProcessIdBitmap[index]);
MOZ_ASSERT(!(sContentProcessIdBitmap[index] & (1ULL << bitIndex)));
MOZ_ASSERT(bitIndex != 0 || index != 0);
sContentProcessIdBitmap[index] |= (1ULL << bitIndex);
value = index * kBitsPerElement + bitIndex;
break;
}
// If we run out of content process IDs, we're in trouble
MOZ_RELEASE_ASSERT(index < ArrayLength(sContentProcessIdBitmap));
sContentParentIdMap->Put(aIPCContentProcessID, value);
return value;
}
void
MsaaIdGenerator::ReleaseContentProcessIDFor(dom::ContentParentId aIPCContentProcessID)
{
MOZ_ASSERT(XRE_IsParentProcess() && NS_IsMainThread());
if (!sContentParentIdMap) {
// Since Content IDs are generated lazily, ContentParent might attempt
// to release an ID that was never allocated to begin with.
return;
}
Maybe<uint32_t> mapping = sContentParentIdMap->GetAndRemove(aIPCContentProcessID);
if (!mapping) {
// Since Content IDs are generated lazily, ContentParent might attempt
// to release an ID that was never allocated to begin with.
return;
}
uint32_t index = mapping.ref() / kBitsPerElement;
MOZ_ASSERT(index < ArrayLength(sContentProcessIdBitmap));
uint64_t mask = 1ULL << (mapping.ref() % kBitsPerElement);
MOZ_ASSERT(sContentProcessIdBitmap[index] & mask);
sContentProcessIdBitmap[index] &= ~mask;
}
} // namespace a11y
} // namespace mozilla
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