StreamCopyThread: Do not let flush interrupt a write

flush calls interrupt() to interrupt a pending read and trigger a
flush.  Unfortunately that interrupt() call can also interrupt a
pending write, putting Jsch in a bad state and triggering "Short read
of block" errors.  Add locking to ensure the flush only interrupts
reads as intended.

Change-Id: Ib105d9e107ae43549ced7e6da29c22ee41cde9d8

org.eclipse.jgit/src/org/eclipse/jgit/util/io/StreamCopyThread.java

@@ -61,6 +61,9 @@ public class StreamCopyThread extends Thread {
 
 	private final AtomicInteger flushCount = new AtomicInteger(0);
 
+	/** Lock held by flush to avoid interrupting a write. */
+	private final Object writeLock;
+
 	/**
 	 * Create a thread to copy data from an input stream to an output stream.
 	 *
@@ -75,6 +78,7 @@ public class StreamCopyThread extends Thread {
 		setName(Thread.currentThread().getName() + "-StreamCopy"); //$NON-NLS-1$
 		src = i;
 		dst = o;
+		writeLock = new Object();
 	}
 
 	/**
@@ -86,8 +90,10 @@ public class StreamCopyThread extends Thread {
 	 */
 	public void flush() {
 		flushCount.incrementAndGet();
+		synchronized (writeLock) {
 			interrupt();
 		}
+	}
 
 	/**
 	 * Request that the thread terminate, and wait for it.
@@ -118,12 +124,12 @@ public class StreamCopyThread extends Thread {
 			for (;;) {
 				try {
 					if (readInterrupted) {
-						try {
+						synchronized (writeLock) {
+							boolean interruptedAgain = Thread.interrupted();
 							dst.flush();
-						} catch (InterruptedIOException e) {
-							// There was a new flush() call during flush previous bytes
-							// need continue read/write/flush for the new bytes
-							continue;
+							if (interruptedAgain) {
+								interrupt();
+							}
 						}
 						readInterrupted = false;
 						if (!flushCount.compareAndSet(flushCountBeforeRead, 0)) {
@@ -148,6 +154,11 @@ public class StreamCopyThread extends Thread {
 					if (n < 0)
 						break;
 
+					synchronized (writeLock) {
+						if (isInterrupted()) {
+							continue;
+						}
+
 						boolean writeInterrupted = false;
 						for (;;) {
 							try {
@@ -163,6 +174,7 @@ public class StreamCopyThread extends Thread {
 								interrupt();
 							break;
 						}
+					}
 				} catch (IOException e) {
 					break;
 				}