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