subprocess.Popen `bufsize` option actually used

The `bufsize` option of the subprocess.Popen module wasn't used (at
all), meaning that the default was usually buffered (platform
dependant), and was also not modifiable.

This was also different from the behavior of the vanilla
subprocess.Popen module

Note that this change the default behavior of the class (buffered
becomes unbuffered in most cases)

gevent/subprocess.py

@@ -245,17 +245,17 @@ class Popen(object):
                 errread = msvcrt.open_osfhandle(errread.Detach(), 0)
 
         if p2cwrite is not None:
-            self.stdin = FileObject(p2cwrite, 'wb')
+            self.stdin = FileObject(p2cwrite, 'wb', bufsize)
         if c2pread is not None:
             if universal_newlines:
-                self.stdout = FileObject(c2pread, 'rU')
+                self.stdout = FileObject(c2pread, 'rU', bufsize)
             else:
-                self.stdout = FileObject(c2pread, 'rb')
+                self.stdout = FileObject(c2pread, 'rb', bufsize)
         if errread is not None:
             if universal_newlines:
-                self.stderr = FileObject(errread, 'rU')
+                self.stderr = FileObject(errread, 'rU', bufsize)
             else:
-                self.stderr = FileObject(errread, 'rb')
+                self.stderr = FileObject(errread, 'rb', bufsize)
 
     def __repr__(self):
         return '<%s at 0x%x pid=%r returncode=%r>' % (self.__class__.__name__, id(self), self.pid, self.returncode)

greentest/test__subprocess.py

@@ -159,6 +159,16 @@ class Test(greentest.TestCase):
         else:
             raise AssertionError('must fail with CalledProcessError')
 
+    def test_popen_bufsize(self):
+        # Test that subprocess has unbuffered output by default
+        # (as the vanilla subprocess module)
+        p = subprocess.Popen([sys.executable, '-u', '-c',
+                              'import sys; sys.stdout.write(sys.stdin.readline())'],
+                             stdin=subprocess.PIPE, stdout=subprocess.PIPE)
+        p.stdin.write('foobar\n')
+        r = p.stdout.readline()
+        self.assertEqual(r, 'foobar\n')
+
 
 if __name__ == '__main__':
     greentest.main()