bpo-35537: subprocess uses os.posix_spawn in some cases

Lib/subprocess.py

@@ -606,6 +606,55 @@ def getoutput(cmd):
  return getstatusoutput(cmd)[1]
 
 
+def _use_posix_spawn():
+ """Check is posix_spawn() can be used for subprocess.
+
+ subprocess requires a posix_spawn() implementation that reports properly
+ errors to the parent process, set errno on the following failures:
+
+ * process attribute actions failed
+ * file actions failed
+ * exec() failed
+ """
+ if _mswindows or not hasattr(os, 'posix_spawn'):
+ # os.posix_spawn() is not available
+ return False
+
+ if sys.platform == 'darwin':
+ # posix_spawn() is a syscall on macOS and properly reports errors
+ return True
+
+ # Check libc name and runtime libc version
+ try:
+ ver = os.confstr('CS_GNU_LIBC_VERSION')
+ # parse 'glibc 2.28' as ('glibc', (2, 28))
+ parts = ver.split(maxsplit=1)
+ if len(parts) != 2:
+ # reject unknown format
+ raise ValueError
+ libc = parts[0]
+ version = tuple(map(int, parts[1].split('.')))
+
+ if libc == 'glibc' and version >= (2, 26):
+ # glibc 2.26 added a pipe to the POSIX implementation
+ # of posix_spawn() to properly report errors to the parent process.
+ return True
+ if sys.platform == 'linux' and libc == 'glibc' and version >= (2, 24):
+ # glibc 2.24 has a new Linux posix_spawn implementation
+ # which properly reports errors to the parent process.
+ return True
+ except (AttributeError, ValueError, OSError):
+ # os.confstr() or CS_GNU_LIBC_VERSION value not available
+ pass
+
+ # By default, consider that the implementation does not properly report
+ # errors.
+ return False
+
+
+_USE_POSIX_SPAWN = _use_posix_spawn()
+
+
 class Popen(object):
  """ Execute a child program in a new process.
 
@@ -1390,6 +1439,23 @@ def _get_handles(self, stdin, stdout, stderr):
  errread, errwrite)
 
 
+ def _posix_spawn(self, args, executable, env, restore_signals):
+ """Execute program using os.posix_spawn()."""
+ if env is None:
+ env = os.environ
+
+ kwargs = {}
+ if restore_signals:
+ # See _Py_RestoreSignals() of Python/pylifecycle.c
+ sigset = []
+ for signame in ('SIGPIPE', 'SIGXFZ', 'SIGXFSZ'):
+ signum = getattr(signal, signame, None)
+ if signum is not None:
+ sigset.append(signum)
+ kwargs['setsigdef'] = sigset
+
+ self.pid = os.posix_spawn(executable, args, env, **kwargs)
+
  def _execute_child(self, args, executable, preexec_fn, close_fds,
  pass_fds, cwd, env,
  startupinfo, creationflags, shell,
@@ -1414,6 +1480,20 @@ def _execute_child(self, args, executable, preexec_fn, close_fds,
 
  if executable is None:
  executable = args[0]
+
+ if (_USE_POSIX_SPAWN
+ and os.path.dirname(executable)
+ and preexec_fn is None
+ and not close_fds
+ and not pass_fds
+ and cwd is None
+ and p2cread == p2cwrite == -1
+ and c2pread == c2pwrite == -1
+ and errread == errwrite == -1
+ and not start_new_session):
+ self._posix_spawn(args, executable, env, restore_signals)
+ return
+
  orig_executable = executable
 
  # For transferring possible exec failure from child to parent.

Lib/test/pythoninfo.py

@@ -601,6 +601,11 @@ def collect_get_config(info_add):
  info_add('%s[%s]' % (prefix, key), repr(config[key]))
 
 
+def collect_subprocess(info_add):
+ import subprocess
+ copy_attributes(info_add, subprocess, 'subprocess.%s', ('_USE_POSIX_SPAWN',))
+
+
 def collect_info(info):
  error = False
  info_add = info.add
@@ -630,6 +635,7 @@ def collect_info(info):
  collect_cc,
  collect_gdbm,
  collect_get_config,
+ collect_subprocess,
 
  # Collecting from tests should be last as they have side effects.
  collect_test_socket,

Misc/NEWS.d/next/Library/2018-12-20-16-24-51.bpo-35537.z4E7aA.rst

@@ -0,0 +1,2 @@
+The :mod:`subprocess` module now uses the :func:`os.posix_spawn` function if
+possible for better performance.