mirror of
https://github.com/classilla/tenfourfox.git
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294 lines
9.0 KiB
C++
294 lines
9.0 KiB
C++
/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
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/* vim: set ts=8 sts=2 et sw=2 tw=80: */
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/* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
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#ifndef nsProxyRelease_h__
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#define nsProxyRelease_h__
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#include "nsIEventTarget.h"
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#include "nsIThread.h"
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#include "nsCOMPtr.h"
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#include "nsAutoPtr.h"
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#include "MainThreadUtils.h"
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#include "mozilla/Likely.h"
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#ifdef XPCOM_GLUE_AVOID_NSPR
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#error NS_ProxyRelease implementation depends on NSPR.
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#endif
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/**
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* Ensure that a nsCOMPtr is released on the target thread.
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*
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* @see NS_ProxyRelease(nsIEventTarget*, nsISupports*, bool)
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*/
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template<class T>
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inline NS_HIDDEN_(nsresult)
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NS_ProxyRelease(nsIEventTarget* aTarget, nsCOMPtr<T>& aDoomed,
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bool aAlwaysProxy = false)
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{
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T* raw = nullptr;
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aDoomed.swap(raw);
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return NS_ProxyRelease(aTarget, raw, aAlwaysProxy);
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}
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/**
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* Ensure that a nsRefPtr is released on the target thread.
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*
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* @see NS_ProxyRelease(nsIEventTarget*, nsISupports*, bool)
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*/
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template<class T>
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inline NS_HIDDEN_(nsresult)
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NS_ProxyRelease(nsIEventTarget* aTarget, RefPtr<T>& aDoomed,
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bool aAlwaysProxy = false)
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{
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T* raw = nullptr;
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aDoomed.swap(raw);
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return NS_ProxyRelease(aTarget, raw, aAlwaysProxy);
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}
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/**
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* Ensures that the delete of a nsISupports object occurs on the target thread.
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*
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* @param aTarget
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* the target thread where the doomed object should be released.
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* @param aDoomed
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* the doomed object; the object to be released on the target thread.
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* @param aAlwaysProxy
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* normally, if NS_ProxyRelease is called on the target thread, then the
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* doomed object will be released directly. However, if this parameter is
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* true, then an event will always be posted to the target thread for
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* asynchronous release.
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*/
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nsresult
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NS_ProxyRelease(nsIEventTarget* aTarget, nsISupports* aDoomed,
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bool aAlwaysProxy = false);
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/**
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* Ensure that a nsCOMPtr is released on the main thread.
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*
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* @see NS_ReleaseOnMainThread( nsISupports*, bool)
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*/
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template<class T>
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inline NS_HIDDEN_(nsresult)
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NS_ReleaseOnMainThread(nsCOMPtr<T>& aDoomed,
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bool aAlwaysProxy = false)
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{
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T* raw = nullptr;
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aDoomed.swap(raw);
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return NS_ReleaseOnMainThread(raw, aAlwaysProxy);
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}
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/**
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* Ensure that a nsRefPtr is released on the main thread.
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*
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* @see NS_ReleaseOnMainThread(nsISupports*, bool)
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*/
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template<class T>
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inline NS_HIDDEN_(nsresult)
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NS_ReleaseOnMainThread(RefPtr<T>& aDoomed,
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bool aAlwaysProxy = false)
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{
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T* raw = nullptr;
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aDoomed.swap(raw);
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return NS_ReleaseOnMainThread(raw, aAlwaysProxy);
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}
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/**
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* Ensures that the delete of a nsISupports object occurs on the main thread.
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*
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* @param aDoomed
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* the doomed object; the object to be released on the main thread.
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* @param aAlwaysProxy
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* normally, if NS_ReleaseOnMainThread is called on the main thread,
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* then the doomed object will be released directly. However, if this
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* parameter is true, then an event will always be posted to the main
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* thread for asynchronous release.
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*/
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inline nsresult
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NS_ReleaseOnMainThread(nsISupports* aDoomed,
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bool aAlwaysProxy = false)
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{
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// NS_ProxyRelease treats a null event target as "the current thread". So a
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// handle on the main thread is only necessary when we're not already on the
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// main thread or the release must happen asynchronously.
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nsCOMPtr<nsIThread> mainThread;
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if (!NS_IsMainThread() || aAlwaysProxy) {
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NS_GetMainThread(getter_AddRefs(mainThread));
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}
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return NS_ProxyRelease(mainThread, aDoomed, aAlwaysProxy);
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}
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/**
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* Class to safely handle main-thread-only pointers off the main thread.
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*
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* Classes like XPCWrappedJS are main-thread-only, which means that it is
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* forbidden to call methods on instances of these classes off the main thread.
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* For various reasons (see bug 771074), this restriction recently began to
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* apply to AddRef/Release as well.
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*
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* This presents a problem for consumers that wish to hold a callback alive
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* on non-main-thread code. A common example of this is the proxy callback
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* pattern, where non-main-thread code holds a strong-reference to the callback
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* object, and dispatches new Runnables (also with a strong reference) to the
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* main thread in order to execute the callback. This involves several AddRef
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* and Release calls on the other thread, which is (now) verboten.
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*
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* The basic idea of this class is to introduce a layer of indirection.
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* nsMainThreadPtrHolder is a threadsafe reference-counted class that internally
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* maintains one strong reference to the main-thread-only object. It must be
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* instantiated on the main thread (so that the AddRef of the underlying object
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* happens on the main thread), but consumers may subsequently pass references
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* to the holder anywhere they please. These references are meant to be opaque
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* when accessed off-main-thread (assertions enforce this).
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*
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* The semantics of RefPtr<nsMainThreadPtrHolder<T> > would be cumbersome, so
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* we also introduce nsMainThreadPtrHandle<T>, which is conceptually identical
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* to the above (though it includes various convenience methods). The basic
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* pattern is as follows.
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*
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* // On the main thread:
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* nsCOMPtr<nsIFooCallback> callback = ...;
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* nsMainThreadPtrHandle<nsIFooCallback> callbackHandle =
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* new nsMainThreadPtrHolder<nsIFooCallback>(callback);
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* // Pass callbackHandle to structs/classes that might be accessed on other
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* // threads.
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*
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* All structs and classes that might be accessed on other threads should store
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* an nsMainThreadPtrHandle<T> rather than an nsCOMPtr<T>.
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*/
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template<class T>
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class nsMainThreadPtrHolder final
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{
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public:
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// We can only acquire a pointer on the main thread. We to fail fast for
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// threading bugs, so by default we assert if our pointer is used or acquired
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// off-main-thread. But some consumers need to use the same pointer for
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// multiple classes, some of which are main-thread-only and some of which
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// aren't. So we allow them to explicitly disable this strict checking.
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explicit nsMainThreadPtrHolder(T* aPtr, bool aStrict = true)
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: mRawPtr(nullptr)
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, mStrict(aStrict)
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{
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// We can only AddRef our pointer on the main thread, which means that the
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// holder must be constructed on the main thread.
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MOZ_ASSERT(!mStrict || NS_IsMainThread());
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NS_IF_ADDREF(mRawPtr = aPtr);
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}
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private:
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// We can be released on any thread.
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~nsMainThreadPtrHolder()
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{
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if (NS_IsMainThread()) {
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NS_IF_RELEASE(mRawPtr);
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} else if (mRawPtr) {
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nsCOMPtr<nsIThread> mainThread;
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NS_GetMainThread(getter_AddRefs(mainThread));
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if (!mainThread) {
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NS_WARNING("Couldn't get main thread! Leaking pointer.");
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return;
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}
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NS_ProxyRelease(mainThread, mRawPtr);
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}
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}
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public:
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T* get()
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{
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// Nobody should be touching the raw pointer off-main-thread.
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if (mStrict && MOZ_UNLIKELY(!NS_IsMainThread())) {
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NS_ERROR("Can't dereference nsMainThreadPtrHolder off main thread");
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MOZ_CRASH();
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}
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return mRawPtr;
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}
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bool operator==(const nsMainThreadPtrHolder<T>& aOther) const
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{
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return mRawPtr == aOther.mRawPtr;
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}
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bool operator!() const
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{
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return !mRawPtr;
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}
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NS_INLINE_DECL_THREADSAFE_REFCOUNTING(nsMainThreadPtrHolder<T>)
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private:
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// Our wrapped pointer.
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T* mRawPtr;
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// Whether to strictly enforce thread invariants in this class.
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bool mStrict;
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// Copy constructor and operator= not implemented. Once constructed, the
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// holder is immutable.
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T& operator=(nsMainThreadPtrHolder& aOther);
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nsMainThreadPtrHolder(const nsMainThreadPtrHolder& aOther);
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};
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template<class T>
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class nsMainThreadPtrHandle
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{
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RefPtr<nsMainThreadPtrHolder<T>> mPtr;
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public:
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nsMainThreadPtrHandle() : mPtr(nullptr) {}
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explicit nsMainThreadPtrHandle(nsMainThreadPtrHolder<T>* aHolder)
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: mPtr(aHolder)
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{
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}
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nsMainThreadPtrHandle(const nsMainThreadPtrHandle& aOther)
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: mPtr(aOther.mPtr)
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{
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}
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nsMainThreadPtrHandle& operator=(const nsMainThreadPtrHandle& aOther)
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{
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mPtr = aOther.mPtr;
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return *this;
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}
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nsMainThreadPtrHandle& operator=(nsMainThreadPtrHolder<T>* aHolder)
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{
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mPtr = aHolder;
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return *this;
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}
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// These all call through to nsMainThreadPtrHolder, and thus implicitly
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// assert that we're on the main thread. Off-main-thread consumers must treat
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// these handles as opaque.
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T* get()
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{
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if (mPtr) {
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return mPtr.get()->get();
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}
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return nullptr;
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}
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const T* get() const
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{
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if (mPtr) {
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return mPtr.get()->get();
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}
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return nullptr;
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}
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operator T*() { return get(); }
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T* operator->() MOZ_NO_ADDREF_RELEASE_ON_RETURN { return get(); }
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// These are safe to call on other threads with appropriate external locking.
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bool operator==(const nsMainThreadPtrHandle<T>& aOther) const
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{
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if (!mPtr || !aOther.mPtr) {
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return mPtr == aOther.mPtr;
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}
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return *mPtr == *aOther.mPtr;
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}
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bool operator!() const {
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return !mPtr || !*mPtr;
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}
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};
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#endif
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