1 files changed, 119 insertions, 0 deletions
diff --git a/xpcom/threads/Monitor.h b/xpcom/threads/Monitor.h
new file mode 100644
index 0000000000..ff8204b5ad
--- /dev/null
+++ b/xpcom/threads/Monitor.h
@@ -0,0 +1,119 @@
+/* -*- 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 mozilla_Monitor_h
+#define mozilla_Monitor_h
+
+#include "mozilla/CondVar.h"
+#include "mozilla/Mutex.h"
+
+namespace mozilla {
+
+/**
+ * Monitor provides a *non*-reentrant monitor: *not* a Java-style
+ * monitor.  If your code needs support for reentrancy, use
+ * ReentrantMonitor instead.  (Rarely should reentrancy be needed.)
+ *
+ * Instead of directly calling Monitor methods, it's safer and simpler
+ * to instead use the RAII wrappers MonitorAutoLock and
+ * MonitorAutoUnlock.
+ */
+class Monitor {
+ public:
+  explicit Monitor(const char* aName)
+      : mMutex(aName), mCondVar(mMutex, "[Monitor.mCondVar]") {}
+
+  ~Monitor() = default;
+
+  void Lock() { mMutex.Lock(); }
+  [[nodiscard]] bool TryLock() { return mMutex.TryLock(); }
+  void Unlock() { mMutex.Unlock(); }
+
+  void Wait() { mCondVar.Wait(); }
+  CVStatus Wait(TimeDuration aDuration) { return mCondVar.Wait(aDuration); }
+
+  void Notify() { mCondVar.Notify(); }
+  void NotifyAll() { mCondVar.NotifyAll(); }
+
+  void AssertCurrentThreadOwns() const { mMutex.AssertCurrentThreadOwns(); }
+
+  void AssertNotCurrentThreadOwns() const {
+    mMutex.AssertNotCurrentThreadOwns();
+  }
+
+ private:
+  Monitor();
+  Monitor(const Monitor&);
+  Monitor& operator=(const Monitor&);
+
+  Mutex mMutex;
+  CondVar mCondVar;
+};
+
+/**
+ * Lock the monitor for the lexical scope instances of this class are
+ * bound to (except for MonitorAutoUnlock in nested scopes).
+ *
+ * The monitor must be unlocked when instances of this class are
+ * created.
+ */
+class MOZ_STACK_CLASS MonitorAutoLock {
+ public:
+  explicit MonitorAutoLock(Monitor& aMonitor) : mMonitor(&aMonitor) {
+    mMonitor->Lock();
+  }
+
+  ~MonitorAutoLock() { mMonitor->Unlock(); }
+
+  void Wait() { mMonitor->Wait(); }
+  CVStatus Wait(TimeDuration aDuration) { return mMonitor->Wait(aDuration); }
+
+  void Notify() { mMonitor->Notify(); }
+  void NotifyAll() { mMonitor->NotifyAll(); }
+
+ private:
+  MonitorAutoLock();
+  MonitorAutoLock(const MonitorAutoLock&);
+  MonitorAutoLock& operator=(const MonitorAutoLock&);
+  static void* operator new(size_t) noexcept(true);
+
+  friend class MonitorAutoUnlock;
+
+  Monitor* mMonitor;
+};
+
+/**
+ * Unlock the monitor for the lexical scope instances of this class
+ * are bound to (except for MonitorAutoLock in nested scopes).
+ *
+ * The monitor must be locked by the current thread when instances of
+ * this class are created.
+ */
+class MOZ_STACK_CLASS MonitorAutoUnlock {
+ public:
+  explicit MonitorAutoUnlock(Monitor& aMonitor) : mMonitor(&aMonitor) {
+    mMonitor->Unlock();
+  }
+
+  explicit MonitorAutoUnlock(MonitorAutoLock& aMonitorLock)
+      : mMonitor(aMonitorLock.mMonitor) {
+    mMonitor->Unlock();
+  }
+
+  ~MonitorAutoUnlock() { mMonitor->Lock(); }
+
+ private:
+  MonitorAutoUnlock();
+  MonitorAutoUnlock(const MonitorAutoUnlock&);
+  MonitorAutoUnlock& operator=(const MonitorAutoUnlock&);
+  static void* operator new(size_t) noexcept(true);
+
+  Monitor* mMonitor;
+};
+
+}  // namespace mozilla
+
+#endif  // mozilla_Monitor_h