Make "git command" and "forall" work on Windows

Python on Windows does not support non blocking file operations.
To workaround this issue, we instead use Threads and a Queue to
simulate non-blocking calls. This is happens only when running
with the native Windows version of Python, meaning Linux and Cygwin
are not affected by this change.

Change-Id: I4ce23827b096c5138f67a85c721f58a12279bb6f

subcmds/forall.py

@@ -15,17 +15,16 @@
 
 from __future__ import print_function
 import errno
-import fcntl
 import multiprocessing
 import re
 import os
-import select
 import signal
 import sys
 import subprocess
 
 from color import Coloring
 from command import Command, MirrorSafeCommand
+import platform_utils
 
 _CAN_COLOR = [
   'branch',
@@ -344,35 +343,25 @@ def DoWork(project, mirror, opt, cmd, shell, cnt, config):
   if opt.project_header:
     out = ForallColoring(config)
     out.redirect(sys.stdout)
-    class sfd(object):
-      def __init__(self, fd, dest):
-        self.fd = fd
-        self.dest = dest
-      def fileno(self):
-        return self.fd.fileno()
-
     empty = True
     errbuf = ''
 
     p.stdin.close()
-    s_in = [sfd(p.stdout, sys.stdout),
-            sfd(p.stderr, sys.stderr)]
+    s_in = platform_utils.FileDescriptorStreams.create()
+    s_in.add(p.stdout, sys.stdout, 'stdout')
+    s_in.add(p.stderr, sys.stderr, 'stderr')
 
-    for s in s_in:
-      flags = fcntl.fcntl(s.fd, fcntl.F_GETFL)
-      fcntl.fcntl(s.fd, fcntl.F_SETFL, flags | os.O_NONBLOCK)
-
-    while s_in:
-      in_ready, _out_ready, _err_ready = select.select(s_in, [], [])
+    while not s_in.is_done:
+      in_ready = s_in.select()
       for s in in_ready:
-        buf = s.fd.read(4096)
+        buf = s.read()
         if not buf:
-          s.fd.close()
+          s.close()
           s_in.remove(s)
           continue
 
         if not opt.verbose:
-          if s.fd != p.stdout:
+          if s.std_name == 'stderr':
             errbuf += buf
             continue