Question

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What's the point of this synchronization?

I’m using the BluetoothChat sample application to make my Bluetooth connection and there’s this thing that’s really bugging me at line 218:

public void write(byte[] out) {
    // Create temporary object
    ConnectedThread r;
    // Synchronize a copy of the ConnectedThread
    synchronized (this) {
        if (mState != STATE_CONNECTED) return;
        r = mConnectedThread;
    }
    // Perform the write unsynchronized
    r.write(out);
}

Why would one need to synchronize a local copy of the ConnectedThread instance, wouldn’t synchronizing the write function do it (be it inside the ConnectedThread or the method above). I guess it’s possible to call write multiple times from different threads at the same time, but I’ve always seen methods synced, not copies of instances.

Answer 1

It is not for ConnectedThread it for mState Synchronize should be used for both read and update.