pager: recreate stdout to make it line-buffered
authorYuya Nishihara <yuya@tcha.org>
Sat, 03 Oct 2015 15:16:33 +0900
changeset 26454 62c5e937f477
parent 26453 1a2578418689
child 26455 f2bf76d3d567
pager: recreate stdout to make it line-buffered We want to see partial command results as soon as possible. But the buffering mode of stdout (= pager's stdin) was set to fully-buffered because it isn't associated with a tty. So, this patch recreates new stdout object to force its buffering mode. Because two file objects are associated with the same stdout fd and their destructors will call close(), one of them must be closed carefully. Python expects that the stdout fd never be closed even after sys.stdout.close() [1], but newstdout has no such hack. So this patch calls newstdout.close() immediately before duplicating the original stdout fd to sys.stdout. operation sys.stdout newstdout fd --------------------- ---------- --------- -------- newstdout.close() open closed closed os.dup2(stdoutfd, ..) open closed open del sys.stdout closed closed open [1] [1]: https://hg.python.org/cpython/file/v2.7.10/Python/sysmodule.c#l1391
hgext/pager.py
--- a/hgext/pager.py	Sat Oct 03 18:48:21 2015 +0900
+++ b/hgext/pager.py	Sat Oct 03 15:16:33 2015 +0900
@@ -70,8 +70,14 @@
                              close_fds=util.closefds, stdin=subprocess.PIPE,
                              stdout=sys.stdout, stderr=sys.stderr)
 
+    # back up original file objects and descriptors
+    olduifout = ui.fout
+    oldstdout = sys.stdout
     stdoutfd = os.dup(sys.stdout.fileno())
     stderrfd = os.dup(sys.stderr.fileno())
+
+    # create new line-buffered stdout so that output can show up immediately
+    ui.fout = sys.stdout = newstdout = os.fdopen(sys.stdout.fileno(), 'wb', 1)
     os.dup2(pager.stdin.fileno(), sys.stdout.fileno())
     if ui._isatty(sys.stderr):
         os.dup2(pager.stdin.fileno(), sys.stderr.fileno())
@@ -81,6 +87,12 @@
         if util.safehasattr(signal, "SIGINT"):
             signal.signal(signal.SIGINT, signal.SIG_IGN)
         pager.stdin.close()
+        ui.fout = olduifout
+        sys.stdout = oldstdout
+        # close new stdout while it's associated with pager; otherwise stdout
+        # fd would be closed when newstdout is deleted
+        newstdout.close()
+        # restore original fds: stdout is open again
         os.dup2(stdoutfd, sys.stdout.fileno())
         os.dup2(stderrfd, sys.stderr.fileno())
         pager.wait()