Initial work

external/android-emugl/shared/emugl/common/condition_variable.h

@@ -0,0 +1,91 @@
+// Copyright (C) 2014 The Android Open Source Project
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifndef EMUGL_CONDITION_VARIABLE_H
+#define EMUGL_CONDITION_VARIABLE_H
+
+#include "emugl/common/mutex.h"
+#include "emugl/common/pod_vector.h"
+
+#ifdef _WIN32
+#include <windows.h>
+#else
+#include <pthread.h>
+#endif
+
+namespace emugl {
+
+// A class that implements a condition variable, which can be used in
+// association with a Mutex to blocking-wait for specific conditions.
+// Useful to implement various synchronization data structures.
+// For an example, see ::emugl::MessageChannel.
+class ConditionVariable {
+public:
+#ifdef _WIN32
+
+    // Default constructor.
+    ConditionVariable();
+
+    // Destructor.
+    ~ConditionVariable();
+
+    // Wait until the condition variable is signaled. Note that spurious
+    // wakeups are always a possibility, so always check the condition
+    // in a loop, i.e. do:
+    //
+    //    while (!condition) { condVar.wait(&lock); }
+    //
+    // instead of:
+    //
+    //    if (!condition) { condVar.wait(&lock); }
+    //
+    void wait(Mutex* userLock);
+
+    // Signal that a condition was reached. This will wake at most one
+    // waiting thread that is blocked on wait().
+    void signal();
+
+private:
+    PodVector<HANDLE> mWaiters;
+    Mutex mLock;
+
+#else  // !_WIN32
+
+    // Note: on Posix systems, make it a naive wrapper around pthread_cond_t.
+
+    ConditionVariable() {
+        pthread_cond_init(&mCond, NULL);
+    }
+
+    ~ConditionVariable() {
+        pthread_cond_destroy(&mCond);
+    }
+
+    void wait(Mutex* userLock) {
+        pthread_cond_wait(&mCond, &userLock->mLock);
+    }
+
+    void signal() {
+        pthread_cond_signal(&mCond);
+    }
+
+private:
+    pthread_cond_t mCond;
+
+#endif  // !_WIN32
+};
+
+}  // namespace emugl
+
+#endif  // EMUGL_CONDITION_VARIABLE_H