First pass at a modem plugin.

src/net/sf/briar/plugins/modem/Modem.java

@@ -6,14 +6,14 @@ import java.io.OutputStream;
 
 /**
  * A modem that can be used for multiple sequential incoming and outgoing
- * calls. If the modem or its input or output streams throw any exceptions they
- * cannot continue to be used.
+ * calls.
  */
 interface Modem {
 
 	/**
-	 * Call this method once after creating the modem and before making any
-	 * calls.
+	 * Call this method after creating the modem and before making any calls.
+	 * If an exception is thrown while using the modem, this method must be
+	 * called again.
 	 */
 	void init() throws IOException;
 

src/net/sf/briar/plugins/modem/ModemImpl.java

@@ -41,7 +41,6 @@ class ModemImpl implements Modem, SerialPortEventListener {
 
 	private int lineLen = 0;
 
-
 	ModemImpl(Executor executor, Callback callback, String portName) {
 		this.executor = executor;
 		this.callback = callback;

src/net/sf/briar/plugins/modem/ModemPlugin.java

@@ -80,10 +80,24 @@ class ModemPlugin implements DuplexPlugin, Modem.Callback {
 		return false;
 	}
 
-	public void stop() {
+	// Synchronized to avoid a race condition with resetModem()
+	public synchronized void stop() {
 		running = false;
 	}
 
+	// Synchronized to avoid a race condition with stop()
+	private synchronized boolean resetModem() {
+		if(!running) return false;
+		try {
+			modem.init();
+			return true;
+		} catch(IOException e) {
+			if(LOG.isLoggable(WARNING)) LOG.warning(e.toString());
+			running = false;
+			return false;
+		}
+	}
+
 	public boolean shouldPoll() {
 		return true;
 	}
@@ -121,9 +135,7 @@ class ModemPlugin implements DuplexPlugin, Modem.Callback {
 			try {
 				if(!modem.dial(number)) continue;
 			} catch(IOException e) {
-				// FIXME: Race condition with stop()
-				running = false;
-				if(start()) continue;
+				if(resetModem()) continue;
 				else break;
 			}
 			ModemTransportConnection conn = new ModemTransportConnection();
@@ -149,9 +161,8 @@ class ModemPlugin implements DuplexPlugin, Modem.Callback {
 		try {
 			if(!modem.dial(number)) return null;
 		} catch(IOException e) {
-			// FIXME: Race condition with stop()
-			running = false;
-			start();
+			// Reinitialise the modem
+			resetModem();
 			return null;
 		}
 		return new ModemTransportConnection();
@@ -199,11 +210,7 @@ class ModemPlugin implements DuplexPlugin, Modem.Callback {
 				if(LOG.isLoggable(WARNING)) LOG.warning(e.toString());
 				exception = true;
 			}
-			if(exception) {
-				// FIXME: Race condition with stop()
-				running = false;
-				start();
-			}
+			if(exception) resetModem();
 			finished.countDown();
 		}