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Commit 67530d65 authored by Hugo Benichi's avatar Hugo Benichi
Browse files

Add volatile qualifier to boolean variable 

DHCP receive thread was spinning on a boolean variable to know when to
stop. That variable had no volatile qualifier, potentially preventing
the thread from stopping at all. Without a volatile qualifier, the reads
and writes in halt() could be reordered in such a way that the running
thread is interrupted before mStopped is set t true. Also, the optimizer
could decide to hoist mStopped in a register inside the running thread,
preventing the loop from exiting.

Change-Id: I5b30c1247808114f0e5b46e230978ee7ea18ab8e
parent 6b34b310

services/net/java/android/net/dhcp/DhcpClient.java

+4 −4
Original line number Diff line number Diff line
@@ -336,17 +336,17 @@ public class DhcpClient extends StateMachine { 
    class ReceiveThread extends Thread {



        private final byte[] mPacket = new byte[DhcpPacket.MAX_LENGTH];

        private boolean stopped = false;

        private volatile boolean mStopped = false;



        public void halt() {

            stopped = true;

            mStopped = true;

            closeSockets();  // Interrupts the read() call the thread is blocked in.

        }



        @Override

        public void run() {

            if (DBG) Log.d(TAG, "Receive thread started");

            while (!stopped) {

            while (!mStopped) {

                int length = 0;  // Or compiler can't tell it's initialized if a parse error occurs.

                try {

                    length = Os.read(mPacketSock, mPacket, 0, mPacket.length);
@@ -355,7 +355,7 @@ public class DhcpClient extends StateMachine { 
                    if (DBG) Log.d(TAG, "Received packet: " + packet);

                    sendMessage(CMD_RECEIVED_PACKET, packet);

                } catch (IOException|ErrnoException e) {

                    if (!stopped) {

                    if (!mStopped) {

                        Log.e(TAG, "Read error", e);

                    }

                    DhcpClientEvent.logEvent(IpConnectivityEvent.IPCE_DHCP_RECV_ERROR,