diff options
Diffstat (limited to 'xpcom/threads/SharedThreadPool.cpp')
| -rw-r--r-- | xpcom/threads/SharedThreadPool.cpp | 221 |
1 files changed, 221 insertions, 0 deletions
diff --git a/xpcom/threads/SharedThreadPool.cpp b/xpcom/threads/SharedThreadPool.cpp new file mode 100644 index 0000000000..a2de1c4495 --- /dev/null +++ b/xpcom/threads/SharedThreadPool.cpp @@ -0,0 +1,221 @@ +/* -*- 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 "mozilla/SharedThreadPool.h" +#include "mozilla/Monitor.h" +#include "mozilla/ReentrantMonitor.h" +#include "mozilla/Services.h" +#include "mozilla/SpinEventLoopUntil.h" +#include "mozilla/StaticPtr.h" +#include "nsTHashMap.h" +#include "nsXPCOMCIDInternal.h" +#include "nsComponentManagerUtils.h" +#include "nsIObserver.h" +#include "nsIObserverService.h" +#include "nsIThreadManager.h" +#include "nsThreadPool.h" + +namespace mozilla { + +// Created and destroyed on the main thread. +static StaticAutoPtr<ReentrantMonitor> sMonitor; + +// Hashtable, maps thread pool name to SharedThreadPool instance. +// Modified only on the main thread. +static StaticAutoPtr<nsTHashMap<nsCStringHashKey, SharedThreadPool*>> sPools; + +static already_AddRefed<nsIThreadPool> CreateThreadPool(const nsCString& aName); + +class SharedThreadPoolShutdownObserver : public nsIObserver { + public: + NS_DECL_ISUPPORTS + NS_DECL_NSIOBSERVER + protected: + virtual ~SharedThreadPoolShutdownObserver() = default; +}; + +NS_IMPL_ISUPPORTS(SharedThreadPoolShutdownObserver, nsIObserver, nsISupports) + +NS_IMETHODIMP +SharedThreadPoolShutdownObserver::Observe(nsISupports* aSubject, + const char* aTopic, + const char16_t* aData) { + MOZ_RELEASE_ASSERT(!strcmp(aTopic, "xpcom-shutdown-threads")); +#ifdef EARLY_BETA_OR_EARLIER + { + ReentrantMonitorAutoEnter mon(*sMonitor); + if (!sPools->IsEmpty()) { + nsAutoCString str; + for (const auto& key : sPools->Keys()) { + str.AppendPrintf("\"%s\" ", nsAutoCString(key).get()); + } + printf_stderr( + "SharedThreadPool in xpcom-shutdown-threads. Waiting for " + "pools %s\n", + str.get()); + } + } +#endif + SharedThreadPool::SpinUntilEmpty(); + sMonitor = nullptr; + sPools = nullptr; + return NS_OK; +} + +void SharedThreadPool::InitStatics() { + MOZ_ASSERT(NS_IsMainThread()); + MOZ_ASSERT(!sMonitor && !sPools); + sMonitor = new ReentrantMonitor("SharedThreadPool"); + sPools = new nsTHashMap<nsCStringHashKey, SharedThreadPool*>(); + nsCOMPtr<nsIObserverService> obsService = + mozilla::services::GetObserverService(); + nsCOMPtr<nsIObserver> obs = new SharedThreadPoolShutdownObserver(); + obsService->AddObserver(obs, "xpcom-shutdown-threads", false); +} + +/* static */ +bool SharedThreadPool::IsEmpty() { + ReentrantMonitorAutoEnter mon(*sMonitor); + return !sPools->Count(); +} + +/* static */ +void SharedThreadPool::SpinUntilEmpty() { + MOZ_ASSERT(NS_IsMainThread()); + SpinEventLoopUntil("SharedThreadPool::SpinUntilEmpty"_ns, []() -> bool { + sMonitor->AssertNotCurrentThreadIn(); + return IsEmpty(); + }); +} + +already_AddRefed<SharedThreadPool> SharedThreadPool::Get( + const nsCString& aName, uint32_t aThreadLimit) { + MOZ_ASSERT(sMonitor && sPools); + ReentrantMonitorAutoEnter mon(*sMonitor); + RefPtr<SharedThreadPool> pool; + + return sPools->WithEntryHandle( + aName, [&](auto&& entry) -> already_AddRefed<SharedThreadPool> { + if (entry) { + pool = entry.Data(); + if (NS_FAILED(pool->EnsureThreadLimitIsAtLeast(aThreadLimit))) { + NS_WARNING("Failed to set limits on thread pool"); + } + } else { + nsCOMPtr<nsIThreadPool> threadPool(CreateThreadPool(aName)); + if (NS_WARN_IF(!threadPool)) { + sPools->Remove(aName); // XXX entry.Remove() + return nullptr; + } + pool = new SharedThreadPool(aName, threadPool); + + // Set the thread and idle limits. Note that we don't rely on the + // EnsureThreadLimitIsAtLeast() call below, as the default thread + // limit is 4, and if aThreadLimit is less than 4 we'll end up with a + // pool with 4 threads rather than what we expected; so we'll have + // unexpected behaviour. + nsresult rv = pool->SetThreadLimit(aThreadLimit); + if (NS_WARN_IF(NS_FAILED(rv))) { + sPools->Remove(aName); // XXX entry.Remove() + return nullptr; + } + + rv = pool->SetIdleThreadLimit(aThreadLimit); + if (NS_WARN_IF(NS_FAILED(rv))) { + sPools->Remove(aName); // XXX entry.Remove() + return nullptr; + } + + entry.Insert(pool.get()); + } + + return pool.forget(); + }); +} + +NS_IMETHODIMP_(MozExternalRefCountType) SharedThreadPool::AddRef(void) { + MOZ_ASSERT(sMonitor); + ReentrantMonitorAutoEnter mon(*sMonitor); + MOZ_ASSERT(int32_t(mRefCnt) >= 0, "illegal refcnt"); + nsrefcnt count = ++mRefCnt; + NS_LOG_ADDREF(this, count, "SharedThreadPool", sizeof(*this)); + return count; +} + +NS_IMETHODIMP_(MozExternalRefCountType) SharedThreadPool::Release(void) { + MOZ_ASSERT(sMonitor); + ReentrantMonitorAutoEnter mon(*sMonitor); + nsrefcnt count = --mRefCnt; + NS_LOG_RELEASE(this, count, "SharedThreadPool"); + if (count) { + return count; + } + + // Remove SharedThreadPool from table of pools. + sPools->Remove(mName); + MOZ_ASSERT(!sPools->Get(mName)); + + // Dispatch an event to the main thread to call Shutdown() on + // the nsIThreadPool. The Runnable here will add a refcount to the pool, + // and when the Runnable releases the nsIThreadPool it will be deleted. + NS_DispatchToMainThread(NewRunnableMethod("nsIThreadPool::Shutdown", mPool, + &nsIThreadPool::Shutdown)); + + // Stabilize refcount, so that if something in the dtor QIs, it won't explode. + mRefCnt = 1; + delete this; + return 0; +} + +NS_IMPL_QUERY_INTERFACE(SharedThreadPool, nsIThreadPool, nsIEventTarget) + +SharedThreadPool::SharedThreadPool(const nsCString& aName, nsIThreadPool* aPool) + : mName(aName), mPool(aPool), mRefCnt(0) {} + +SharedThreadPool::~SharedThreadPool() = default; + +nsresult SharedThreadPool::EnsureThreadLimitIsAtLeast(uint32_t aLimit) { + // We limit the number of threads that we use. Note that we + // set the thread limit to the same as the idle limit so that we're not + // constantly creating and destroying threads (see Bug 881954). When the + // thread pool threads shutdown they dispatch an event to the main thread + // to call nsIThread::Shutdown(), and if we're very busy that can take a + // while to run, and we end up with dozens of extra threads. Note that + // threads that are idle for 60 seconds are shutdown naturally. + uint32_t existingLimit = 0; + nsresult rv; + + rv = mPool->GetThreadLimit(&existingLimit); + NS_ENSURE_SUCCESS(rv, rv); + if (aLimit > existingLimit) { + rv = mPool->SetThreadLimit(aLimit); + NS_ENSURE_SUCCESS(rv, rv); + } + + rv = mPool->GetIdleThreadLimit(&existingLimit); + NS_ENSURE_SUCCESS(rv, rv); + if (aLimit > existingLimit) { + rv = mPool->SetIdleThreadLimit(aLimit); + NS_ENSURE_SUCCESS(rv, rv); + } + + return NS_OK; +} + +static already_AddRefed<nsIThreadPool> CreateThreadPool( + const nsCString& aName) { + nsCOMPtr<nsIThreadPool> pool = new nsThreadPool(); + + nsresult rv = pool->SetName(aName); + NS_ENSURE_SUCCESS(rv, nullptr); + + rv = pool->SetThreadStackSize(nsIThreadManager::kThreadPoolStackSize); + NS_ENSURE_SUCCESS(rv, nullptr); + + return pool.forget(); +} + +} // namespace mozilla |