issue #156: add extra debugging around Latch

Change from writing '\x00' to writing '\x7f', and verify that is the
byte that woke the sleeping thread. Add a bunch more IO logging.

mitogen/core.py

@@ -913,30 +913,36 @@ class Latch(object):
         self.queue = []
         self.wake_socks = []
 
-    def _tls_init(self):
-        if not hasattr(_tls, 'rsock'):
-            _tls.rsock, _tls.wsock = socket.socketpair()
-            set_cloexec(_tls.rsock.fileno())
-            set_cloexec(_tls.wsock.fileno())
-
     def close(self):
         self.lock.acquire()
         try:
             self.closed = True
-            for sock in self.wake_socks:
-                self._wake(sock)
+            while self.wake_socks:
+                self._wake(self.wake_socks.pop())
         finally:
             self.lock.release()
 
     def empty(self):
         return len(self.queue) == 0
 
+    def _tls_init(self):
+        if not hasattr(_tls, 'rsock'):
+            _tls.rsock, _tls.wsock = socket.socketpair()
+            set_cloexec(_tls.rsock.fileno())
+            set_cloexec(_tls.wsock.fileno())
+
     def get(self, timeout=None, block=True):
+        _vv and IOLOG.debug(
+            '%r.get(timeout=%r, block=%r)',
+            self, timeout, block
+        )
+
         self.lock.acquire()
         try:
             if self.closed:
                 raise LatchError()
             if self.queue:
+                _vv and IOLOG.debug('%r.get() -> %r', self, self.queue[0])
                 return self.queue.pop(0)
             if not block:
                 raise TimeoutError()
@@ -945,6 +951,7 @@ class Latch(object):
         finally:
             self.lock.release()
 
+        _vv and IOLOG.debug('%r.get() -> sleeping', self)
         rfds, _, _ = restart(select.select, [_tls.rsock], [], [], timeout)
         assert len(rfds) or timeout is not None
 
@@ -958,7 +965,8 @@ class Latch(object):
                 raise TimeoutError()
 
             assert _tls.rsock in rfds
-            _tls.rsock.recv(1)
+            assert _tls.rsock.recv(1) == '\x7f'
+            _vv and IOLOG.debug('%r.get() wake -> %r', self, self.queue[0])
             return self.queue.pop(0)
         finally:
             self.lock.release()
@@ -979,11 +987,21 @@ class Latch(object):
 
     def _wake(self, sock):
         try:
-            os.write(sock.fileno(), '\x00')
+            os.write(sock.fileno(), '\x7f')
         except OSError, e:
             if e[0] != errno.EBADF:
                 raise
 
+    def __repr__(self):
+        rsock = getattr(_tls, 'rsock', None)
+        wsock = getattr(_tls, 'wsock', None)
+        return 'Latch(%r, t=%r, r=%r, w=%r)' % (
+            id(self),
+            threading.currentThread().name,
+            rsock and rsock.fileno(),
+            wsock and wsock.fileno(),
+        )
+
 
 class Waker(BasicStream):
     """