# HG changeset patch
# User Yuya Nishihara <yuya@tcha.org>
# Date 2016-02-29 04:41:54
# Node ID 7f2313450e865e8822ef306e03341ab73d7450eb
# Parent  bc5d0e6fd9f37ad12f5736f535e6895572dd019f

cmdserver: write channel header and payload by a single write() call

This makes a channeledoutput thread-safe as long as the underlying fwrite() is
thread-safe. Both POSIX and Windows implementations are documented as MT-safe.

MT-safety is necessary to use ui.fout and ui.ferr in hgweb.

diff --git a/mercurial/commandserver.py b/mercurial/commandserver.py
--- a/mercurial/commandserver.py
+++ b/mercurial/commandserver.py
@@ -54,8 +54,8 @@ class channeledoutput(object):
     def write(self, data):
         if not data:
             return
-        self.out.write(struct.pack('>cI', self.channel, len(data)))
-        self.out.write(data)
+        # single write() to guarantee the same atomicity as the underlying file
+        self.out.write(struct.pack('>cI', self.channel, len(data)) + data)
         self.out.flush()
 
     def __getattr__(self, attr):