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authorMatt A. Tobin <mattatobin@localhost.localdomain>2018-02-02 04:16:08 -0500
committerMatt A. Tobin <mattatobin@localhost.localdomain>2018-02-02 04:16:08 -0500
commit5f8de423f190bbb79a62f804151bc24824fa32d8 (patch)
tree10027f336435511475e392454359edea8e25895d /xpcom/glue/nsProxyRelease.h
parent49ee0794b5d912db1f95dce6eb52d781dc210db5 (diff)
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Add m-esr52 at 52.6.0
Diffstat (limited to 'xpcom/glue/nsProxyRelease.h')
-rw-r--r--xpcom/glue/nsProxyRelease.h353
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diff --git a/xpcom/glue/nsProxyRelease.h b/xpcom/glue/nsProxyRelease.h
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+/* -*- 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/. */
+
+#ifndef nsProxyRelease_h__
+#define nsProxyRelease_h__
+
+#include "nsIEventTarget.h"
+#include "nsIThread.h"
+#include "nsCOMPtr.h"
+#include "nsAutoPtr.h"
+#include "MainThreadUtils.h"
+#include "nsThreadUtils.h"
+#include "mozilla/Likely.h"
+#include "mozilla/Move.h"
+#include "mozilla/TypeTraits.h"
+#include "mozilla/Unused.h"
+
+#ifdef XPCOM_GLUE_AVOID_NSPR
+#error NS_ProxyRelease implementation depends on NSPR.
+#endif
+
+namespace detail {
+
+template<typename T>
+class ProxyReleaseEvent : public mozilla::Runnable
+{
+public:
+ explicit ProxyReleaseEvent(already_AddRefed<T> aDoomed)
+ : mDoomed(aDoomed.take()) {}
+
+ NS_IMETHOD Run() override
+ {
+ NS_IF_RELEASE(mDoomed);
+ return NS_OK;
+ }
+
+private:
+ T* MOZ_OWNING_REF mDoomed;
+};
+
+template<typename T>
+void
+ProxyRelease(nsIEventTarget* aTarget, already_AddRefed<T> aDoomed, bool aAlwaysProxy)
+{
+ // Auto-managing release of the pointer.
+ RefPtr<T> doomed = aDoomed;
+ nsresult rv;
+
+ if (!doomed || !aTarget) {
+ return;
+ }
+
+ if (!aAlwaysProxy) {
+ bool onCurrentThread = false;
+ rv = aTarget->IsOnCurrentThread(&onCurrentThread);
+ if (NS_SUCCEEDED(rv) && onCurrentThread) {
+ return;
+ }
+ }
+
+ nsCOMPtr<nsIRunnable> ev = new ProxyReleaseEvent<T>(doomed.forget());
+
+ rv = aTarget->Dispatch(ev, NS_DISPATCH_NORMAL);
+ if (NS_FAILED(rv)) {
+ NS_WARNING("failed to post proxy release event, leaking!");
+ // It is better to leak the aDoomed object than risk crashing as
+ // a result of deleting it on the wrong thread.
+ }
+}
+
+template<bool nsISupportsBased>
+struct ProxyReleaseChooser
+{
+ template<typename T>
+ static void ProxyRelease(nsIEventTarget* aTarget,
+ already_AddRefed<T> aDoomed,
+ bool aAlwaysProxy)
+ {
+ ::detail::ProxyRelease(aTarget, mozilla::Move(aDoomed), aAlwaysProxy);
+ }
+};
+
+template<>
+struct ProxyReleaseChooser<true>
+{
+ // We need an intermediate step for handling classes with ambiguous
+ // inheritance to nsISupports.
+ template<typename T>
+ static void ProxyRelease(nsIEventTarget* aTarget,
+ already_AddRefed<T> aDoomed,
+ bool aAlwaysProxy)
+ {
+ ProxyReleaseISupports(aTarget, ToSupports(aDoomed.take()), aAlwaysProxy);
+ }
+
+ static void ProxyReleaseISupports(nsIEventTarget* aTarget,
+ nsISupports* aDoomed,
+ bool aAlwaysProxy);
+};
+
+} // namespace detail
+
+/**
+ * Ensures that the delete of a smart pointer occurs on the target thread.
+ *
+ * @param aTarget
+ * the target thread where the doomed object should be released.
+ * @param aDoomed
+ * the doomed object; the object to be released on the target thread.
+ * @param aAlwaysProxy
+ * normally, if NS_ProxyRelease is called on the target thread, then the
+ * doomed object will be released directly. However, if this parameter is
+ * true, then an event will always be posted to the target thread for
+ * asynchronous release.
+ */
+template<class T>
+inline NS_HIDDEN_(void)
+NS_ProxyRelease(nsIEventTarget* aTarget, already_AddRefed<T> aDoomed,
+ bool aAlwaysProxy = false)
+{
+ ::detail::ProxyReleaseChooser<mozilla::IsBaseOf<nsISupports, T>::value>
+ ::ProxyRelease(aTarget, mozilla::Move(aDoomed), aAlwaysProxy);
+}
+
+/**
+ * Ensures that the delete of a smart pointer occurs on the main thread.
+ *
+ * @param aDoomed
+ * the doomed object; the object to be released on the main thread.
+ * @param aAlwaysProxy
+ * normally, if NS_ReleaseOnMainThread is called on the main thread,
+ * then the doomed object will be released directly. However, if this
+ * parameter is true, then an event will always be posted to the main
+ * thread for asynchronous release.
+ */
+template<class T>
+inline NS_HIDDEN_(void)
+NS_ReleaseOnMainThread(already_AddRefed<T> aDoomed,
+ bool aAlwaysProxy = false)
+{
+ // NS_ProxyRelease treats a null event target as "the current thread". So a
+ // handle on the main thread is only necessary when we're not already on the
+ // main thread or the release must happen asynchronously.
+ nsCOMPtr<nsIThread> mainThread;
+ if (!NS_IsMainThread() || aAlwaysProxy) {
+ nsresult rv = NS_GetMainThread(getter_AddRefs(mainThread));
+
+ if (NS_FAILED(rv)) {
+ MOZ_ASSERT_UNREACHABLE("Could not get main thread; leaking an object!");
+ mozilla::Unused << aDoomed.take();
+ return;
+ }
+ }
+
+ NS_ProxyRelease(mainThread, mozilla::Move(aDoomed), aAlwaysProxy);
+}
+
+/**
+ * Class to safely handle main-thread-only pointers off the main thread.
+ *
+ * Classes like XPCWrappedJS are main-thread-only, which means that it is
+ * forbidden to call methods on instances of these classes off the main thread.
+ * For various reasons (see bug 771074), this restriction recently began to
+ * apply to AddRef/Release as well.
+ *
+ * This presents a problem for consumers that wish to hold a callback alive
+ * on non-main-thread code. A common example of this is the proxy callback
+ * pattern, where non-main-thread code holds a strong-reference to the callback
+ * object, and dispatches new Runnables (also with a strong reference) to the
+ * main thread in order to execute the callback. This involves several AddRef
+ * and Release calls on the other thread, which is (now) verboten.
+ *
+ * The basic idea of this class is to introduce a layer of indirection.
+ * nsMainThreadPtrHolder is a threadsafe reference-counted class that internally
+ * maintains one strong reference to the main-thread-only object. It must be
+ * instantiated on the main thread (so that the AddRef of the underlying object
+ * happens on the main thread), but consumers may subsequently pass references
+ * to the holder anywhere they please. These references are meant to be opaque
+ * when accessed off-main-thread (assertions enforce this).
+ *
+ * The semantics of RefPtr<nsMainThreadPtrHolder<T> > would be cumbersome, so
+ * we also introduce nsMainThreadPtrHandle<T>, which is conceptually identical
+ * to the above (though it includes various convenience methods). The basic
+ * pattern is as follows.
+ *
+ * // On the main thread:
+ * nsCOMPtr<nsIFooCallback> callback = ...;
+ * nsMainThreadPtrHandle<nsIFooCallback> callbackHandle =
+ * new nsMainThreadPtrHolder<nsIFooCallback>(callback);
+ * // Pass callbackHandle to structs/classes that might be accessed on other
+ * // threads.
+ *
+ * All structs and classes that might be accessed on other threads should store
+ * an nsMainThreadPtrHandle<T> rather than an nsCOMPtr<T>.
+ */
+template<class T>
+class nsMainThreadPtrHolder final
+{
+public:
+ // We can only acquire a pointer on the main thread. We to fail fast for
+ // threading bugs, so by default we assert if our pointer is used or acquired
+ // off-main-thread. But some consumers need to use the same pointer for
+ // multiple classes, some of which are main-thread-only and some of which
+ // aren't. So we allow them to explicitly disable this strict checking.
+ explicit nsMainThreadPtrHolder(T* aPtr, bool aStrict = true)
+ : mRawPtr(nullptr)
+ , mStrict(aStrict)
+ {
+ // We can only AddRef our pointer on the main thread, which means that the
+ // holder must be constructed on the main thread.
+ MOZ_ASSERT(!mStrict || NS_IsMainThread());
+ NS_IF_ADDREF(mRawPtr = aPtr);
+ }
+ explicit nsMainThreadPtrHolder(already_AddRefed<T> aPtr, bool aString = true)
+ : mRawPtr(aPtr.take())
+ , mStrict(aString)
+ {
+ // Since we don't need to AddRef the pointer, this constructor is safe to
+ // call on any thread.
+ }
+
+private:
+ // We can be released on any thread.
+ ~nsMainThreadPtrHolder()
+ {
+ if (NS_IsMainThread()) {
+ NS_IF_RELEASE(mRawPtr);
+ } else if (mRawPtr) {
+ NS_ReleaseOnMainThread(dont_AddRef(mRawPtr));
+ }
+ }
+
+public:
+ T* get()
+ {
+ // Nobody should be touching the raw pointer off-main-thread.
+ if (mStrict && MOZ_UNLIKELY(!NS_IsMainThread())) {
+ NS_ERROR("Can't dereference nsMainThreadPtrHolder off main thread");
+ MOZ_CRASH();
+ }
+ return mRawPtr;
+ }
+
+ bool operator==(const nsMainThreadPtrHolder<T>& aOther) const
+ {
+ return mRawPtr == aOther.mRawPtr;
+ }
+ bool operator!() const
+ {
+ return !mRawPtr;
+ }
+
+ NS_INLINE_DECL_THREADSAFE_REFCOUNTING(nsMainThreadPtrHolder<T>)
+
+private:
+ // Our wrapped pointer.
+ T* mRawPtr;
+
+ // Whether to strictly enforce thread invariants in this class.
+ bool mStrict;
+
+ // Copy constructor and operator= not implemented. Once constructed, the
+ // holder is immutable.
+ T& operator=(nsMainThreadPtrHolder& aOther);
+ nsMainThreadPtrHolder(const nsMainThreadPtrHolder& aOther);
+};
+
+template<class T>
+class nsMainThreadPtrHandle
+{
+ RefPtr<nsMainThreadPtrHolder<T>> mPtr;
+
+public:
+ nsMainThreadPtrHandle() : mPtr(nullptr) {}
+ MOZ_IMPLICIT nsMainThreadPtrHandle(decltype(nullptr)) : mPtr(nullptr) {}
+ explicit nsMainThreadPtrHandle(nsMainThreadPtrHolder<T>* aHolder)
+ : mPtr(aHolder)
+ {
+ }
+ explicit nsMainThreadPtrHandle(
+ already_AddRefed<nsMainThreadPtrHolder<T>> aHolder)
+ : mPtr(aHolder)
+ {
+ }
+ nsMainThreadPtrHandle(const nsMainThreadPtrHandle& aOther)
+ : mPtr(aOther.mPtr)
+ {
+ }
+ nsMainThreadPtrHandle& operator=(const nsMainThreadPtrHandle& aOther)
+ {
+ mPtr = aOther.mPtr;
+ return *this;
+ }
+ nsMainThreadPtrHandle& operator=(nsMainThreadPtrHolder<T>* aHolder)
+ {
+ mPtr = aHolder;
+ return *this;
+ }
+
+ // These all call through to nsMainThreadPtrHolder, and thus implicitly
+ // assert that we're on the main thread. Off-main-thread consumers must treat
+ // these handles as opaque.
+ T* get()
+ {
+ if (mPtr) {
+ return mPtr.get()->get();
+ }
+ return nullptr;
+ }
+ const T* get() const
+ {
+ if (mPtr) {
+ return mPtr.get()->get();
+ }
+ return nullptr;
+ }
+
+ operator T*() { return get(); }
+ T* operator->() MOZ_NO_ADDREF_RELEASE_ON_RETURN { return get(); }
+
+ // These are safe to call on other threads with appropriate external locking.
+ bool operator==(const nsMainThreadPtrHandle<T>& aOther) const
+ {
+ if (!mPtr || !aOther.mPtr) {
+ return mPtr == aOther.mPtr;
+ }
+ return *mPtr == *aOther.mPtr;
+ }
+ bool operator!=(const nsMainThreadPtrHandle<T>& aOther) const
+ {
+ return !operator==(aOther);
+ }
+ bool operator==(decltype(nullptr)) const { return mPtr == nullptr; }
+ bool operator!=(decltype(nullptr)) const { return mPtr != nullptr; }
+ bool operator!() const {
+ return !mPtr || !*mPtr;
+ }
+};
+
+namespace mozilla {
+
+template<typename T>
+using PtrHolder = nsMainThreadPtrHolder<T>;
+
+template<typename T>
+using PtrHandle = nsMainThreadPtrHandle<T>;
+
+} // namespace mozilla
+
+#endif