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diff --git a/media/libstagefright/wifi-display/TimeSyncer.h b/media/libstagefright/wifi-display/TimeSyncer.h
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+++ b/media/libstagefright/wifi-display/TimeSyncer.h
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+/*
+ * Copyright 2013, 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 TIME_SYNCER_H_
+
+#define TIME_SYNCER_H_
+
+#include <media/stagefright/foundation/AHandler.h>
+
+namespace android {
+
+struct ANetworkSession;
+
+/*
+   TimeSyncer allows us to synchronize time between a client and a server.
+   The client sends a UDP packet containing its send-time to the server,
+   the server sends that packet back to the client amended with information
+   about when it was received as well as the time the reply was sent back.
+   Finally the client receives the reply and has now enough information to
+   compute the clock offset between client and server assuming that packet
+   exchange is symmetric, i.e. time for a packet client->server and
+   server->client is roughly equal.
+   This exchange is repeated a number of times and the average offset computed
+   over the 30% of packets that had the lowest roundtrip times.
+   The offset is determined every 10 secs to account for slight differences in
+   clock frequency.
+*/
+struct TimeSyncer : public AHandler {
+    enum {
+        kWhatError,
+        kWhatTimeOffset,
+    };
+    TimeSyncer(
+            const sp<ANetworkSession> &netSession,
+            const sp<AMessage> &notify);
+
+    void startServer(unsigned localPort);
+    void startClient(const char *remoteHost, unsigned remotePort);
+
+protected:
+    virtual ~TimeSyncer();
+
+    virtual void onMessageReceived(const sp<AMessage> &msg);
+
+private:
+    enum {
+        kWhatStartServer,
+        kWhatStartClient,
+        kWhatUDPNotify,
+        kWhatSendPacket,
+        kWhatTimedOut,
+    };
+
+    struct TimeInfo {
+        int64_t mT1;  // client timestamp at send
+        int64_t mT2;  // server timestamp at receive
+        int64_t mT3;  // server timestamp at send
+        int64_t mT4;  // client timestamp at receive
+    };
+
+    enum {
+        kNumPacketsPerBatch = 30,
+    };
+    static const int64_t kTimeoutDelayUs = 500000ll;
+    static const int64_t kBatchDelayUs = 10000000ll;  // every 10 secs
+
+    sp<ANetworkSession> mNetSession;
+    sp<AMessage> mNotify;
+
+    bool mIsServer;
+    bool mConnected;
+    int32_t mUDPSession;
+    uint32_t mSeqNo;
+    double mTotalTimeUs;
+
+    Vector<TimeInfo> mHistory;
+
+    int64_t mPendingT1;
+    int32_t mTimeoutGeneration;
+
+    void postSendPacket(int64_t delayUs = 0ll);
+
+    void postTimeout();
+    void cancelTimeout();
+
+    void notifyError(status_t err);
+    void notifyOffset();
+
+    static int CompareRountripTime(const TimeInfo *ti1, const TimeInfo *ti2);
+
+    DISALLOW_EVIL_CONSTRUCTORS(TimeSyncer);
+};
+
+}  // namespace android
+
+#endif  // TIME_SYNCER_H_