[lit] Use os.devnull instead of named temp files

[vsk]

Summary

Use os.devnull instead of tempfiles when substituting '/dev/null' on Windows machines. This should make the bots just a bit speedier.

I'd appreciate it if someone could test this patch on Windows -- I don't have access to it.

[vsk]

Ping.

[ygao]

Hi, sorry for the delay.
I tested your change on a 64-bit Windows 7 machine and it works fine. It seems a good idea to use os.devnull instead of a temporary file. Thanks.
I am not very familiar with the code myself to give a LGTM, so a second review would be appreciated.

[vsk]

@ygao thanks!

I'll leave this up for another day before committing. I'll work through any post-commit feedback as it comes.

llvm/trunk/utils/lit/lit/TestRunner.py

def __init__(self, command, message):
         self.command = command
         self.message = message
 
 kIsWindows = platform.system() == 'Windows'
 
 # Don't use close_fds on Windows.
 kUseCloseFDs = not kIsWindows
 
-# Use temporary files to replace /dev/null on Windows.
-kAvoidDevNull = kIsWindows
-
 class ShellEnvironment(object):
 
     """Mutable shell environment containing things like CWD and env vars.
 
     Environment variables are not implemented, but cwd tracking is.
     """
 
     def __init__(self, cwd, env):
if cmd.commands[0].args[0] == 'cd':
         # The cd builtin always succeeds. If the directory does not exist, the
         # following Popen calls will fail instead.
         return 0
 
     procs = []
     input = subprocess.PIPE
     stderrTempFiles = []
     opened_files = []
-    named_temp_files = []
     # To avoid deadlock, we use a single stderr stream for piped
     # output. This is null until we have seen some output using
     # stderr.
     for i,j in enumerate(cmd.commands):
         # Reference the global environment by default.
         cmd_shenv = shenv
         if j.args[0] == 'env':
             # Create a copy of the global environment and modify it for this one
for i,j in enumerate(cmd.commands):
                     result = subprocess.STDOUT
             elif r == (2,):
                 if index != 2:
                     raise InternalShellError(j,"Unsupported redirect on stdout")
                 result = subprocess.PIPE
             else:
                 if r[2] is None:
                     redir_filename = None
-                    if kAvoidDevNull and r[0] == '/dev/null':
-                        r[2] = tempfile.TemporaryFile(mode=r[1])
+                    if kIsWindows and r[0] == '/dev/null':
+                        r[2] = open(os.devnull, r[1])
                     elif kIsWindows and r[0] == '/dev/tty':
                         # Simulate /dev/tty on Windows.
                         # "CON" is a special filename for the console.
                         r[2] = open("CON", r[1])
                     else:
                         # Make sure relative paths are relative to the cwd.
                         redir_filename = os.path.join(cmd_shenv.cwd, r[0])
                         r[2] = open(redir_filename, r[1])
for i,j in enumerate(cmd.commands):
             exe_in_cwd = os.path.join(cmd_shenv.cwd, args[0])
             if os.path.isfile(exe_in_cwd):
                 executable = exe_in_cwd
         if not executable:
             executable = lit.util.which(args[0], cmd_shenv.env['PATH'])
         if not executable:
             raise InternalShellError(j, '%r: command not found' % j.args[0])
 
-        # Replace uses of /dev/null with temporary files.
-        if kAvoidDevNull:
+        if kIsWindows:
+            # Replace uses of /dev/null with the Windows equivalent.
             for i,arg in enumerate(args):
                 if arg == "/dev/null":
-                    f = tempfile.NamedTemporaryFile(delete=False)
-                    f.close()
-                    named_temp_files.append(f.name)
-                    args[i] = f.name
+                    args[i] = os.devnull
 
         try:
             procs.append(subprocess.Popen(args, cwd=cmd_shenv.cwd,
                                           executable = executable,
                                           stdin = stdin,
                                           stdout = stdout,
                                           stderr = stderr,
                                           env = cmd_shenv.env,
for i,(out,err) in enumerate(procData):
                 exitCode = res
             elif res < 0:
                 exitCode = min(exitCode, res)
             else:
                 exitCode = max(exitCode, res)
         else:
             exitCode = res
 
-    # Remove any named temporary files we created.
-    for f in named_temp_files:
-        try:
-            os.remove(f)
-        except OSError:
-            pass
-
     if cmd.negate:
         exitCode = not exitCode
 
     return exitCode
 
 def executeScriptInternal(test, litConfig, tmpBase, commands, cwd):
     cmds = []
     for ln in commands: