+/* -*- 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 SharedThreadPool_h_

+#define SharedThreadPool_h_

+

+#include <queue>

+#include "mozilla/RefPtr.h"

+#include "nsThreadUtils.h"

+#include "nsIThreadManager.h"

+#include "nsIThreadPool.h"

+#include "nsISupports.h"

+#include "nsISupportsImpl.h"

+#include "nsCOMPtr.h"

+

+namespace mozilla {

+

+// Wrapper that makes an nsIThreadPool a singleton, and provides a

+// consistent threadsafe interface to get instances. Callers simply get a

+// SharedThreadPool by the name of its nsIThreadPool. All get requests of

+// the same name get the same SharedThreadPool. Users must store a reference

+// to the pool, and when the last reference to a SharedThreadPool is dropped

+// the pool is shutdown and deleted. Users aren't required to manually

+// shutdown the pool, and can release references on any thread. This can make

+// it significantly easier to use thread pools, because the caller doesn't need

+// to worry about joining and tearing it down.

+//

+// On Windows all threads in the pool have MSCOM initialized with

+// COINIT_MULTITHREADED. Note that not all users of MSCOM use this mode see [1],

+// and mixing MSCOM objects between the two is terrible for performance, and can

+// cause some functions to fail. So be careful when using Win32 APIs on a

+// SharedThreadPool, and avoid sharing objects if at all possible.

+//

+// [1] https://dxr.mozilla.org/mozilla-central/search?q=coinitialize&redirect=false

+class SharedThreadPool : public nsIThreadPool

+{

+public:

+

+ // Gets (possibly creating) the shared thread pool singleton instance with

+ // thread pool named aName.

+ static already_AddRefed<SharedThreadPool> Get(const nsCString& aName,

+ uint32_t aThreadLimit = 4);

+

+ // We implement custom threadsafe AddRef/Release pair, that destroys the

+ // the shared pool singleton when the refcount drops to 0. The addref/release

+ // are implemented using locking, so it's not recommended that you use them

+ // in a tight loop.

+ NS_IMETHOD QueryInterface(REFNSIID aIID, void** aInstancePtr) override;

+ NS_IMETHOD_(MozExternalRefCountType) AddRef(void) override;

+ NS_IMETHOD_(MozExternalRefCountType) Release(void) override;

+

+ // Forward behaviour to wrapped thread pool implementation.

+ NS_FORWARD_SAFE_NSITHREADPOOL(mPool);

+

+ // Call this when dispatching from an event on the same

+ // threadpool that is about to complete. We should not create a new thread

+ // in that case since a thread is about to become idle.

+ nsresult DispatchFromEndOfTaskInThisPool(nsIRunnable *event)

+ {

+ return Dispatch(event, NS_DISPATCH_AT_END);

+ }

+

+ NS_IMETHOD DispatchFromScript(nsIRunnable *event, uint32_t flags) override {

+ return Dispatch(event, flags);

+ }

+

+ NS_IMETHOD Dispatch(already_AddRefed<nsIRunnable> event, uint32_t flags) override

+ { return !mEventTarget ? NS_ERROR_NULL_POINTER : mEventTarget->Dispatch(Move(event), flags); }

+

+ NS_IMETHOD DelayedDispatch(already_AddRefed<nsIRunnable>, uint32_t) override

+ { return NS_ERROR_NOT_IMPLEMENTED; }

+

+ using nsIEventTarget::Dispatch;

+

+ NS_IMETHOD IsOnCurrentThread(bool *_retval) override { return !mEventTarget ? NS_ERROR_NULL_POINTER : mEventTarget->IsOnCurrentThread(_retval); }

+

+ // Creates necessary statics. Called once at startup.

+ static void InitStatics();

+

+ // Spins the event loop until all thread pools are shutdown.

+ // *Must* be called on the main thread.

+ static void SpinUntilEmpty();

+

+#if defined(MOZ_ASAN)

+ // Use the system default in ASAN builds, because the default is assumed to be

+ // larger than the size we want to use and is hopefully sufficient for ASAN.

+ static const uint32_t kStackSize = nsIThreadManager::DEFAULT_STACK_SIZE;

+#elif defined(XP_WIN) || defined(XP_MACOSX) || defined(LINUX)

+ static const uint32_t kStackSize = (256 * 1024);

+#else

+ // All other platforms use their system defaults.

+ static const uint32_t kStackSize = nsIThreadManager::DEFAULT_STACK_SIZE;

+#endif

+

+private:

+

+ // Returns whether there are no pools in existence at the moment.

+ static bool IsEmpty();

+

+ // Creates a singleton SharedThreadPool wrapper around aPool.

+ // aName is the name of the aPool, and is used to lookup the

+ // SharedThreadPool in the hash table of all created pools.

+ SharedThreadPool(const nsCString& aName,

+ nsIThreadPool* aPool);

+ virtual ~SharedThreadPool();

+

+ nsresult EnsureThreadLimitIsAtLeast(uint32_t aThreadLimit);

+

+ // Name of mPool.

+ const nsCString mName;

+

+ // Thread pool being wrapped.

+ nsCOMPtr<nsIThreadPool> mPool;

+

+ // Refcount. We implement custom ref counting so that the thread pool is

+ // shutdown in a threadsafe manner and singletonness is preserved.

+ nsrefcnt mRefCnt;

+

+ // mPool QI'd to nsIEventTarget. We cache this, so that we can use

+ // NS_FORWARD_SAFE_NSIEVENTTARGET above.

+ nsCOMPtr<nsIEventTarget> mEventTarget;

+};

+

+} // namespace mozilla

+

+#endif // SharedThreadPool_h_