Initial work

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

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+// Copyright 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_COMMON_MESSAGE_CHANNEL_H
+#define EMUGL_COMMON_MESSAGE_CHANNEL_H
+
+#include "emugl/common/condition_variable.h"
+#include "emugl/common/mutex.h"
+
+#include <stddef.h>
+
+namespace emugl {
+
+// Base non-templated class used to reduce the amount of template
+// specialization.
+class MessageChannelBase {
+public:
+    // Constructor. |capacity| is the buffer capacity in messages.
+    MessageChannelBase(size_t capacity);
+
+    // Destructor.
+    ~MessageChannelBase();
+
+protected:
+    // Call this method in the sender thread before writing a new message.
+    // This returns the position of the available slot in the message array
+    // where to copy the new fixed-size message. After the copy, call
+    // afterWrite().
+    size_t beforeWrite();
+
+    // To be called after beforeWrite() and copying a new fixed-size message
+    // into the array. This signal the receiver thread that there is a new
+    // incoming message.
+    void afterWrite();
+
+    // Call this method in the receiver thread before reading a new message.
+    // This returns the position in the message array where the new message
+    // can be read. Caller must process the message, then call afterRead().
+    size_t beforeRead();
+
+    // To be called in the receiver thread after beforeRead() and processing
+    // the corresponding message.
+    void afterRead();
+
+private:
+    size_t mPos;
+    size_t mCount;
+    size_t mCapacity;
+    Mutex mLock;
+    ConditionVariable mCanRead;
+    ConditionVariable mCanWrite;
+};
+
+// Helper class used to implement an uni-directional IPC channel between
+// two threads. The channel can be used to send fixed-size messages of type
+// |T|, with an internal buffer size of |CAPACITY| items. All calls are
+// blocking.
+//
+// Usage is pretty straightforward:
+//
+//   - From the sender thread, call send(msg);
+//   - From the receiver thread, call receive(&msg);
+//
+template <typename T, size_t CAPACITY>
+class MessageChannel : public MessageChannelBase {
+public:
+    MessageChannel() : MessageChannelBase(CAPACITY) {}
+
+    void send(const T& msg) {
+        size_t pos = beforeWrite();
+        mItems[pos] = msg;
+        afterWrite();
+    }
+
+    void receive(T* msg) {
+        size_t pos = beforeRead();
+        *msg = mItems[pos];
+        afterRead();
+    }
+
+private:
+    T mItems[CAPACITY];
+};
+
+}  // namespace emugl
+
+#endif  // EMUGL_COMMON_MESSAGE_CHANNEL_H