master: Include RID in worker exception messages

This helps when debugging unexpected shutdown problems
after the fact.

artiq/master/worker.py

@@ -165,12 +165,15 @@ class Worker:
             ifs, timeout=self.send_timeout,
             return_when=asyncio.FIRST_COMPLETED)
         if all(f.cancelled() for f in fs):
-            raise WorkerTimeout("Timeout sending data to worker")
+            raise WorkerTimeout(
+                "Timeout sending data to worker (RID {})".format(self.rid))
         for f in fs:
             if not f.cancelled() and f.done():
                 f.result()  # raise any exceptions
         if cancellable and self.closed.is_set():
-            raise WorkerError("Data transmission to worker cancelled")
+            raise WorkerError(
+                "Data transmission to worker cancelled (RID {})".format(
+                    self.rid))
 
     async def _recv(self, timeout):
         assert self.io_lock.locked()
@@ -178,16 +181,22 @@ class Worker:
             [self.ipc.readline(), self.closed.wait()],
             timeout=timeout, return_when=asyncio.FIRST_COMPLETED)
         if all(f.cancelled() for f in fs):
-            raise WorkerTimeout("Timeout receiving data from worker")
+            raise WorkerTimeout(
+                "Timeout receiving data from worker (RID {})".format(self.rid))
         if self.closed.is_set():
-            raise WorkerError("Data transmission to worker cancelled")
+            raise WorkerError(
+                "Receiving data from worker cancelled (RID {})".format(
+                    self.rid))
         line = fs[0].result()
         if not line:
-            raise WorkerError("Worker ended while attempting to receive data")
+            raise WorkerError(
+                "Worker ended while attempting to receive data (RID {})".
+                format(self.rid))
         try:
             obj = pyon.decode(line.decode())
         except:
-            raise WorkerError("Worker sent invalid PYON data")
+            raise WorkerError("Worker sent invalid PYON data (RID {})".format(
+                self.rid))
         return obj
 
     async def _handle_worker_requests(self):