It's time to bring subprocess42 to depot_tools.

subprocess42.py

Index: subprocess42.py
diff --git a/subprocess42.py b/subprocess42.py
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+# Copyright 2013 The LUCI Authors. All rights reserved.
+# Use of this source code is governed by the Apache v2.0 license that can be
+# found in the LICENSE file.
+
+# This is a direct vendored copy of the original which is located at:
+#   https://github.com/luci/luci-py/blob/master/client/utils/subprocess42.py
+#   at commit 45eab10a17a55f1978f3bfa02c35457dee1c64e4.
+
+"""subprocess42 is the answer to life the universe and everything.
+
+It has the particularity of having a Popen implementation that can yield output
+as it is produced while implementing a timeout and NOT requiring the use of
+worker threads.
+
+Example:
+  Wait for a child process with a timeout, send SIGTERM, wait a grace period
+  then send SIGKILL:
+
+    def wait_terminate_then_kill(proc, timeout, grace):
+      try:
+        return proc.wait(timeout)
+      except subprocess42.TimeoutExpired:
+        proc.terminate()
+        try:
+          return proc.wait(grace)
+        except subprocess42.TimeoutExpired:
+          proc.kill()
+        return proc.wait()
+
+
+TODO(maruel): Add VOID support like subprocess2.
+"""
+
+import contextlib
+import errno
+import os
+import signal
+import threading
+import time
+
+import subprocess
+
+from subprocess import CalledProcessError, PIPE, STDOUT  # pylint: disable=W0611
+from subprocess import list2cmdline
+
+
+# Default maxsize argument.
+MAX_SIZE = 16384
+
+
+if subprocess.mswindows:
+  import msvcrt  # pylint: disable=F0401
+  from ctypes import wintypes
+  from ctypes import windll
+
+
+  # Which to be received depends on how this process was called and outside the
+  # control of this script. See Popen docstring for more details.
+  STOP_SIGNALS = (signal.SIGBREAK, signal.SIGTERM)
+
+
+  def ReadFile(handle, desired_bytes):
+    """Calls kernel32.ReadFile()."""
+    c_read = wintypes.DWORD()
+    buff = wintypes.create_string_buffer(desired_bytes+1)
+    windll.kernel32.ReadFile(
+        handle, buff, desired_bytes, wintypes.byref(c_read), None)
+    # NULL terminate it.
+    buff[c_read.value] = '\x00'
+    return wintypes.GetLastError(), buff.value
+
+  def PeekNamedPipe(handle):
+    """Calls kernel32.PeekNamedPipe(). Simplified version."""
+    c_avail = wintypes.DWORD()
+    c_message = wintypes.DWORD()
+    success = windll.kernel32.PeekNamedPipe(
+        handle, None, 0, None, wintypes.byref(c_avail),
+        wintypes.byref(c_message))
+    if not success:
+      raise OSError(wintypes.GetLastError())
+    return c_avail.value
+
+  def recv_multi_impl(conns, maxsize, timeout):
+    """Reads from the first available pipe.
+
+    It will immediately return on a closed connection, independent of timeout.
+
+    Arguments:
+    - maxsize: Maximum number of bytes to return. Defaults to MAX_SIZE.
+    - timeout: If None, it is blocking. If 0 or above, will return None if no
+          data is available within |timeout| seconds.
+
+    Returns:
+      tuple(int(index), str(data), bool(closed)).
+    """
+    assert conns
+    assert timeout is None or isinstance(timeout, (int, float)), timeout
+    maxsize = max(maxsize or MAX_SIZE, 1)
+
+    # TODO(maruel): Use WaitForMultipleObjects(). Python creates anonymous pipes
+    # for proc.stdout and proc.stderr but they are implemented as named pipes on
+    # Windows. Since named pipes are not waitable object, they can't be passed
+    # as-is to WFMO(). So this means N times CreateEvent(), N times ReadFile()
+    # and finally WFMO(). This requires caching the events handles in the Popen
+    # object and remembering the pending ReadFile() calls. This will require
+    # some re-architecture to store the relevant event handle and OVERLAPPEDIO
+    # object in Popen or the file object.
+    start = time.time()
+    handles = [
+      (i, msvcrt.get_osfhandle(c.fileno())) for i, c in enumerate(conns)
+    ]
+    while True:
+      for index, handle in handles:
+        try:
+          avail = min(PeekNamedPipe(handle), maxsize)
+          if avail:
+            return index, ReadFile(handle, avail)[1], False
+        except OSError:
+          # The pipe closed.
+          return index, None, True
+
+      if timeout is not None and (time.time() - start) >= timeout:
+        return None, None, False
+      # Polling rocks.
+      time.sleep(0.001)
+
+else:
+  import fcntl  # pylint: disable=F0401
+  import select
+
+
+  # Signals that mean this process should exit quickly.
+  STOP_SIGNALS = (signal.SIGINT, signal.SIGTERM)
+
+
+  def recv_multi_impl(conns, maxsize, timeout):
+    """Reads from the first available pipe.
+
+    It will immediately return on a closed connection, independent of timeout.
+
+    Arguments:
+    - maxsize: Maximum number of bytes to return. Defaults to MAX_SIZE.
+    - timeout: If None, it is blocking. If 0 or above, will return None if no
+          data is available within |timeout| seconds.
+
+    Returns:
+      tuple(int(index), str(data), bool(closed)).
+    """
+    assert conns
+    assert timeout is None or isinstance(timeout, (int, float)), timeout
+    maxsize = max(maxsize or MAX_SIZE, 1)
+
+    # select(timeout=0) will block, it has to be a value > 0.
+    if timeout == 0:
+      timeout = 0.001
+    try:
+      r, _, _ = select.select(conns, [], [], timeout)
+    except select.error:
+      r = None
+    if not r:
+      return None, None, False
+
+    conn = r[0]
+    # Temporarily make it non-blocking.
+    # TODO(maruel): This is not very efficient when the caller is doing this in
+    # a loop. Add a mechanism to have the caller handle this.
+    flags = fcntl.fcntl(conn, fcntl.F_GETFL)
+    if not conn.closed:
+      # pylint: disable=E1101
+      fcntl.fcntl(conn, fcntl.F_SETFL, flags | os.O_NONBLOCK)
+    try:
+      try:
+        data = conn.read(maxsize)
+      except IOError as e:
+        # On posix, this means the read would block.
+        if e.errno == errno.EAGAIN:
+          return conns.index(conn), None, False
+        raise e
+
+      if not data:
+        # On posix, this means the channel closed.
+        return conns.index(conn), None, True
+
+      return conns.index(conn), data, False
+    finally:
+      if not conn.closed:
+        fcntl.fcntl(conn, fcntl.F_SETFL, flags)
+
+
+class TimeoutExpired(Exception):
+  """Compatible with python3 subprocess."""
+  def __init__(self, cmd, timeout, output=None, stderr=None):
+    self.cmd = cmd
+    self.timeout = timeout
+    self.output = output
+    # Non-standard:
+    self.stderr = stderr
+    super(TimeoutExpired, self).__init__(str(self))
+
+  def __str__(self):
+    return "Command '%s' timed out after %s seconds" % (self.cmd, self.timeout)
+
+
+class Popen(subprocess.Popen):
+  """Adds timeout support on stdout and stderr.
+
+  Inspired by
+  http://code.activestate.com/recipes/440554-module-to-allow-asynchronous-subprocess-use-on-win/
+
+  Unlike subprocess, yield_any(), recv_*(), communicate() will close stdout and
+  stderr once the child process closes them, after all the data is read.
+
+  Arguments:
+  - detached: If True, the process is created in a new process group. On
+    Windows, use CREATE_NEW_PROCESS_GROUP. On posix, use os.setpgid(0, 0).
+
+  Additional members:
+  - start: timestamp when this process started.
+  - end: timestamp when this process exited, as seen by this process.
+  - detached: If True, the child process was started as a detached process.
+  - gid: process group id, if any.
+  - duration: time in seconds the process lasted.
+
+  Additional methods:
+  - yield_any(): yields output until the process terminates.
+  - recv_any(): reads from stdout and/or stderr with optional timeout.
+  - recv_out() & recv_err(): specialized version of recv_any().
+  """
+  # subprocess.Popen.__init__() is not threadsafe; there is a race between
+  # creating the exec-error pipe for the child and setting it to CLOEXEC during
+  # which another thread can fork and cause the pipe to be inherited by its
+  # descendents, which will cause the current Popen to hang until all those
+  # descendents exit. Protect this with a lock so that only one fork/exec can
+  # happen at a time.
+  popen_lock = threading.Lock()
+
+  def __init__(self, args, **kwargs):
+    assert 'creationflags' not in kwargs
+    assert 'preexec_fn' not in kwargs, 'Use detached=True instead'
+    self.start = time.time()
+    self.end = None
+    self.gid = None
+    self.detached = kwargs.pop('detached', False)
+    if self.detached:
+      if subprocess.mswindows:
+        kwargs['creationflags'] = subprocess.CREATE_NEW_PROCESS_GROUP
+      else:
+        kwargs['preexec_fn'] = lambda: os.setpgid(0, 0)
+    with self.popen_lock:
+      super(Popen, self).__init__(args, **kwargs)
+    self.args = args
+    if self.detached and not subprocess.mswindows:
+      try:
+        self.gid = os.getpgid(self.pid)
+      except OSError:
+        # sometimes the process can run+finish before we collect its pgid. fun.
+        pass
+
+  def duration(self):
+    """Duration of the child process.
+
+    It is greater or equal to the actual time the child process ran. It can be
+    significantly higher than the real value if neither .wait() nor .poll() was
+    used.
+    """
+    return (self.end or time.time()) - self.start
+
+  # pylint: disable=arguments-differ,redefined-builtin
+  def communicate(self, input=None, timeout=None):
+    """Implements python3's timeout support.
+
+    Unlike wait(), timeout=0 is considered the same as None.
+
+    Raises:
+    - TimeoutExpired when more than timeout seconds were spent waiting for the
+      process.
+    """
+    if not timeout:
+      return super(Popen, self).communicate(input=input)
+
+    assert isinstance(timeout, (int, float)), timeout
+
+    if self.stdin or self.stdout or self.stderr:
+      stdout = '' if self.stdout else None
+      stderr = '' if self.stderr else None
+      t = None
+      if input is not None:
+        assert self.stdin, (
+            'Can\'t use communicate(input) if not using '
+            'Popen(stdin=subprocess42.PIPE')
+        # TODO(maruel): Switch back to non-threading.
+        def write():
+          try:
+            self.stdin.write(input)
+          except IOError:
+            pass
+        t = threading.Thread(name='Popen.communicate', target=write)
+        t.daemon = True
+        t.start()
+
+      try:
+        if self.stdout or self.stderr:
+          start = time.time()
+          end = start + timeout
+          def remaining():
+            return max(end - time.time(), 0)
+          for pipe, data in self.yield_any(timeout=remaining):
+            if pipe is None:
+              raise TimeoutExpired(self.args, timeout, stdout, stderr)
+            assert pipe in ('stdout', 'stderr'), pipe
+            if pipe == 'stdout':
+              stdout += data
+            else:
+              stderr += data
+        else:
+          # Only stdin is piped.
+          self.wait(timeout=timeout)
+      finally:
+        if t:
+          try:
+            self.stdin.close()
+          except IOError:
+            pass
+          t.join()
+    else:
+      # No pipe. The user wanted to use wait().
+      self.wait(timeout=timeout)
+      return None, None
+
+    # Indirectly initialize self.end.
+    self.wait()
+    return stdout, stderr
+
+  def wait(self, timeout=None):  # pylint: disable=arguments-differ
+    """Implements python3's timeout support.
+
+    Raises:
+    - TimeoutExpired when more than timeout seconds were spent waiting for the
+      process.
+    """
+    assert timeout is None or isinstance(timeout, (int, float)), timeout
+    if timeout is None:
+      super(Popen, self).wait()
+    elif self.returncode is None:
+      if subprocess.mswindows:
+        WAIT_TIMEOUT = 258
+        result = subprocess._subprocess.WaitForSingleObject(
+            self._handle, int(timeout * 1000))
+        if result == WAIT_TIMEOUT:
+          raise TimeoutExpired(self.args, timeout)
+        self.returncode = subprocess._subprocess.GetExitCodeProcess(
+            self._handle)
+      else:
+        # If you think the following code is horrible, it's because it is
+        # inspired by python3's stdlib.
+        end = time.time() + timeout
+        delay = 0.001
+        while True:
+          try:
+            pid, sts = subprocess._eintr_retry_call(
+                os.waitpid, self.pid, os.WNOHANG)
+          except OSError as e:
+            if e.errno != errno.ECHILD:
+              raise
+            pid = self.pid
+            sts = 0
+          if pid == self.pid:
+            # This sets self.returncode.
+            self._handle_exitstatus(sts)
+            break
+          remaining = end - time.time()
+          if remaining <= 0:
+            raise TimeoutExpired(self.args, timeout)
+          delay = min(delay * 2, remaining, .05)
+          time.sleep(delay)
+
+    if not self.end:
+      # communicate() uses wait() internally.
+      self.end = time.time()
+    return self.returncode
+
+  def poll(self):
+    ret = super(Popen, self).poll()
+    if ret is not None and not self.end:
+      self.end = time.time()
+    return ret
+
+  def yield_any(self, maxsize=None, timeout=None):
+    """Yields output until the process terminates.
+
+    Unlike wait(), does not raise TimeoutExpired.
+
+    Yields:
+      (pipename, data) where pipename is either 'stdout', 'stderr' or None in
+      case of timeout or when the child process closed one of the pipe(s) and
+      all pending data on the pipe was read.
+
+    Arguments:
+    - maxsize: See recv_any(). Can be a callable function.
+    - timeout: If None, the call is blocking. If set, yields None, None if no
+          data is available within |timeout| seconds. It resets itself after
+          each yield. Can be a callable function.
+    """
+    assert self.stdout or self.stderr
+    if timeout is not None:
+      # timeout=0 effectively means that the pipe is continuously polled.
+      if isinstance(timeout, (int, float)):
+        assert timeout >= 0, timeout
+        old_timeout = timeout
+        timeout = lambda: old_timeout
+      else:
+        assert callable(timeout), timeout
+
+    if maxsize is not None and not callable(maxsize):
+      assert isinstance(maxsize, (int, float)), maxsize
+
+    last_yield = time.time()
+    while self.poll() is None:
+      to = (None if timeout is None
+            else max(timeout() - (time.time() - last_yield), 0))
+      t, data = self.recv_any(
+          maxsize=maxsize() if callable(maxsize) else maxsize, timeout=to)
+      if data or to is 0:
+        yield t, data
+        last_yield = time.time()
+
+    # Read all remaining output in the pipes.
+    # There is 3 cases:
+    # - pipes get closed automatically by the calling process before it exits
+    # - pipes are closed automated by the OS
+    # - pipes are kept open due to grand-children processes outliving the
+    #   children process.
+    while True:
+      ms = maxsize
+      if callable(maxsize):
+        ms = maxsize()
+      # timeout=0 is mainly to handle the case where a grand-children process
+      # outlives the process started.
+      t, data = self.recv_any(maxsize=ms, timeout=0)
+      if not data:
+        break
+      yield t, data
+
+  def recv_any(self, maxsize=None, timeout=None):
+    """Reads from the first pipe available from stdout and stderr.
+
+    Unlike wait(), it does not throw TimeoutExpired.
+
+    Arguments:
+    - maxsize: Maximum number of bytes to return. Defaults to MAX_SIZE.
+    - timeout: If None, it is blocking. If 0 or above, will return None if no
+          data is available within |timeout| seconds.
+
+    Returns:
+      tuple(pipename or None, str(data)). pipename is one of 'stdout' or
+      'stderr'.
+    """
+    # recv_multi_impl will early exit on a closed connection. Loop accordingly
+    # to simplify call sites.
+    while True:
+      pipes = [
+        x for x in ((self.stderr, 'stderr'), (self.stdout, 'stdout')) if x[0]
+      ]
+      # If both stdout and stderr have the exact file handle, they are
+      # effectively the same pipe. Deduplicate it since otherwise it confuses
+      # recv_multi_impl().
+      if len(pipes) == 2 and self.stderr.fileno() == self.stdout.fileno():
+        pipes.pop(0)
+
+      if not pipes:
+        return None, None
+      start = time.time()
+      conns, names = zip(*pipes)
+      index, data, closed = recv_multi_impl(conns, maxsize, timeout)
+      if index is None:
+        return index, data
+      if closed:
+        self._close(names[index])
+        if not data:
+          # Loop again. The other pipe may still be open.
+          if timeout:
+            timeout -= (time.time() - start)
+          continue
+
+      if self.universal_newlines and data:
+        data = self._translate_newlines(data)
+      return names[index], data
+
+  def recv_out(self, maxsize=None, timeout=None):
+    """Reads from stdout synchronously with timeout."""
+    return self._recv('stdout', maxsize, timeout)
+
+  def recv_err(self, maxsize=None, timeout=None):
+    """Reads from stderr synchronously with timeout."""
+    return self._recv('stderr', maxsize, timeout)
+
+  def terminate(self):
+    """Tries to do something saner on Windows that the stdlib.
+
+    Windows:
+      self.detached/CREATE_NEW_PROCESS_GROUP determines what can be used:
+      - If set, only SIGBREAK can be sent and it is sent to a single process.
+      - If not set, in theory only SIGINT can be used and *all processes* in
+         the processgroup receive it. In practice, we just kill the process.
+      See http://msdn.microsoft.com/library/windows/desktop/ms683155.aspx
+      The default on Windows is to call TerminateProcess() always, which is not
+      useful.
+
+    On Posix, always send SIGTERM.
+    """
+    try:
+      if subprocess.mswindows and self.detached:
+        return self.send_signal(signal.CTRL_BREAK_EVENT)
+      super(Popen, self).terminate()
+    except OSError:
+      # The function will throw if the process terminated in-between. Swallow
+      # this.
+      pass
+
+  def kill(self):
+    """Kills the process and its children if possible.
+
+    Swallows exceptions and return True on success.
+    """
+    if self.gid:
+      try:
+        os.killpg(self.gid, signal.SIGKILL)
+      except OSError:
+        return False
+    else:
+      try:
+        super(Popen, self).kill()
+      except OSError:
+        return False
+    return True
+
+  def _close(self, which):
+    """Closes either stdout or stderr."""
+    getattr(self, which).close()
+    setattr(self, which, None)
+
+  def _recv(self, which, maxsize, timeout):
+    """Reads from one of stdout or stderr synchronously with timeout."""
+    conn = getattr(self, which)
+    if conn is None:
+      return None
+    _, data, closed = recv_multi_impl([conn], maxsize, timeout)
+    if closed:
+      self._close(which)
+    if self.universal_newlines and data:
+      data = self._translate_newlines(data)
+    return data
+
+
+@contextlib.contextmanager
+def set_signal_handler(signals, handler):
+  """Temporarilly override signals handler.
+
+  Useful when waiting for a child process to handle signals like SIGTERM, so the
+  signal can be propagated to the child process.
+  """
+  previous = {s: signal.signal(s, handler) for s in signals}
+  try:
+    yield
+  finally:
+    for sig, h in previous.iteritems():
+      signal.signal(sig, h)
+
+
+def call(*args, **kwargs):
+  """Adds support for timeout."""
+  timeout = kwargs.pop('timeout', None)
+  return Popen(*args, **kwargs).wait(timeout)
+
+
+def check_call(*args, **kwargs):
+  """Adds support for timeout."""
+  retcode = call(*args, **kwargs)
+  if retcode:
+    raise CalledProcessError(retcode, kwargs.get('args') or args[0])
+  return 0
+
+
+def check_output(*args, **kwargs):
+  """Adds support for timeout."""
+  timeout = kwargs.pop('timeout', None)
+  if 'stdout' in kwargs:
+    raise ValueError('stdout argument not allowed, it will be overridden.')
+  process = Popen(stdout=PIPE, *args, **kwargs)
+  output, _ = process.communicate(timeout=timeout)
+  retcode = process.poll()
+  if retcode:
+    raise CalledProcessError(retcode, kwargs.get('args') or args[0], output)
+  return output
+
+
+def call_with_timeout(args, timeout, **kwargs):
+  """Runs an executable; kill it in case of timeout."""
+  proc = Popen(args, stdin=subprocess.PIPE, stdout=subprocess.PIPE, **kwargs)
+  try:
+    out, err = proc.communicate(timeout=timeout)
+  except TimeoutExpired as e:
+    out = e.output
+    err = e.stderr
+    proc.kill()
+    proc.wait()
+  return out, err, proc.returncode, proc.duration()