streams: Fix _try_write method; add more debug stats

Author: 1st1

uvloop/handles/stream.pyx

@@ -158,18 +158,11 @@ cdef class UVStream(UVBaseTransport):
             self.__reading_stopped()
 
     cdef inline _try_write(self, object data):
-        if self._get_write_buffer_size():
-            # Don't try to write anything as we already have some
-            # data in the write buffers.
-            return
-
         cdef:
             ssize_t written
             int fd
             Py_buffer py_buf
 
-        # Let's try to send the data right away.
-
         fd = self._fileno()
         PyObject_GetBuffer(data, &py_buf, PyBUF_SIMPLE)
         written = system.send(fd, <char*>py_buf.buf, py_buf.len, 0)
@@ -185,21 +178,27 @@ cdef class UVStream(UVBaseTransport):
                 exc = convert_error(-errno.errno)
                 self._fatal_error(exc, True)
 
+        IF DEBUG:
+            if written > 0:
+                self._loop._debug_stream_write_tries += 1
+
         return written
 
     cdef inline _write(self, object data):
         cdef:
             int err
-            int sent
             _StreamWriteContext ctx
 
         self._ensure_alive()
 
-        sent = self._try_write(data)
-        if sent > 0:
-            if sent == len(data):
-                return
-            data = data[sent:]
+        if not self._get_write_buffer_size():
+            # Try to write without polling only when there is
+            # no data in write buffers.
+            sent = self._try_write(data)
+            if sent > 0:
+                if sent == len(data):
+                    return
+                data = data[sent:]
 
         ctx = _StreamWriteContext.new(self, data)
 

uvloop/loop.pxd

@@ -97,6 +97,7 @@ cdef class Loop:
             readonly uint64_t _debug_stream_read_eof_cb_errors_total
             readonly uint64_t _debug_stream_read_errors_total
 
+            readonly uint64_t _debug_stream_write_tries
             readonly uint64_t _debug_stream_write_errors_total
             readonly uint64_t _debug_stream_write_ctx_total
             readonly uint64_t _debug_stream_write_ctx_cnt

uvloop/loop.pyx

@@ -97,6 +97,7 @@ cdef class Loop:
             self._debug_stream_shutdown_errors_total = 0
             self._debug_stream_listen_errors_total = 0
 
+            self._debug_stream_write_tries = 0
             self._debug_stream_write_errors_total = 0
             self._debug_stream_write_ctx_total = 0
             self._debug_stream_write_ctx_cnt = 0
@@ -759,6 +760,8 @@ cdef class Loop:
             print('--- Streams debug info: ---')
             print('Write errors:              {}'.format(
                 self._debug_stream_write_errors_total))
+            print('Write without poll:        {}'.format(
+                self._debug_stream_write_tries))
             print('Write contexts:            {: <8} | {}'.format(
                 self._debug_stream_write_ctx_cnt,
                 self._debug_stream_write_ctx_total))