os: emulate non-blocking API in posix_read/write

gevent/os.py

@@ -32,7 +32,7 @@ def _map_errors(func, *args):
     try:
         return func(*args)
     except IOError, e:
-        # IOError is structered like OSError in that it has two args: an error
+        # IOError is structured like OSError in that it has two args: an error
         # number and a error string. So we can just re-raise OSError passing it
         # the IOError args. If at some point we want to catch other errors and
         # map those to OSError as well, we need to make sure that it follows
@@ -48,13 +48,16 @@ def posix_read(fd, n):
     hub, event = None, None
     while True:
         flags = _map_errors(fcntl.fcntl, fd, fcntl.F_GETFL, 0)
-        if not flags & os.O_NONBLOCK:
+        blocking_fd = not bool(flags & os.O_NONBLOCK)
+        if blocking_fd:
             _map_errors(fcntl.fcntl, fd, fcntl.F_SETFL, flags|os.O_NONBLOCK)
         try:
             return _read(fd, n)
         except OSError, e:
             if e.errno not in ignored_errors:
                 raise
+            if e.errno == EAGAIN and not blocking_fd:
+                raise
             sys.exc_clear()
         finally:
             # Be sure to restore the fcntl flags before we switch into the hub.
@@ -62,7 +65,7 @@ def posix_read(fd, n):
             # (e.g. when using ttys/ptys). Those other file descriptors are
             # impacted by our change of flags, so we should restore them
             # before any other code can possibly run.
-            if not flags & os.O_NONBLOCK:
+            if blocking_fd:
                 _map_errors(fcntl.fcntl, fd, fcntl.F_SETFL, flags)
         if hub is None:
             hub = get_hub()
@@ -76,17 +79,20 @@ def posix_write(fd, buf):
     hub, event = None, None
     while True:
         flags = _map_errors(fcntl.fcntl, fd, fcntl.F_GETFL, 0)
-        if not flags & os.O_NONBLOCK:
+        blocking_fd = not bool(flags & os.O_NONBLOCK)
+        if blocking_fd:
             _map_errors(fcntl.fcntl, fd, fcntl.F_SETFL, flags|os.O_NONBLOCK)
         try:
             return _write(fd, buf)
         except OSError, e:
             if e.errno not in ignored_errors:
                 raise
+            if e.errno == EAGAIN and not blocking_fd:
+                raise
             sys.exc_clear()
         finally:
             # See note in posix_read().
-            if not flags & os.O_NONBLOCK:
+            if blocking_fd:
                 _map_errors(fcntl.fcntl, fd, fcntl.F_SETFL, flags)
         if hub is None:
             hub = get_hub()

greentest/test__os.py

@@ -8,6 +8,11 @@ try:
 except ImportError:
     fcntl = None
 
+try:
+    import errno
+except ImportError:
+    errno = None
+
 
 class TestOS(TestCase):
 
@@ -57,6 +62,59 @@ class TestOS(TestCase):
         flags = fcntl.fcntl(w, fcntl.F_GETFL, 0)
         assert not flags & os.O_NONBLOCK
 
+    def test_o_nonblock_read(self):
+        if fcntl is None or errno is None:
+            return
+        r, w = os.pipe()
+
+        rflags = fcntl.fcntl(r, fcntl.F_GETFL, 0)
+        fcntl.fcntl(r, fcntl.F_SETFL, rflags|os.O_NONBLOCK)
+
+        gotEAGAIN = False
+        try:
+            os.read(r, 3)
+        except OSError, e:
+            if e.errno != errno.EAGAIN:
+                raise
+            gotEAGAIN = True
+
+        assert gotEAGAIN
+
+        os.write(w, "foo")
+        data = os.read(r, 3)
+        assert data == "foo"
+
+        gotEAGAIN = False
+        try:
+            os.read(r, 3)
+        except OSError, e:
+            if e.errno != errno.EAGAIN:
+                raise
+            gotEAGAIN = True
+
+        assert gotEAGAIN
+
+    def test_o_nonblock_write(self):
+        if fcntl is None or errno is None:
+            return
+        r, w = os.pipe()
+
+        wflags = fcntl.fcntl(r, fcntl.F_GETFL, 0)
+        fcntl.fcntl(w, fcntl.F_SETFL, wflags|os.O_NONBLOCK)
+
+        data = "d" * 1000000
+
+        # fill output buffer to force EAGAIN in next os.write() call
+        os.write(w, data)
+        gotEAGAIN = False
+        try:
+            os.write(w, data)
+        except OSError, e:
+            if e.errno != errno.EAGAIN:
+                raise
+            gotEAGAIN = True
+        assert gotEAGAIN
+
 
 if __name__ == '__main__':
     main()