AsynchronousLock: use subprocess if no threads

1 files changed, 138 insertions, 17 deletions

diff --git a/pym/_emerge/AsynchronousLock.py b/pym/_emerge/AsynchronousLock.py
index 6eb90b4e4..bce81ed5c 100644
--- a/pym/_emerge/AsynchronousLock.py
+++ b/pym/_emerge/AsynchronousLock.py
@@ -3,18 +3,76 @@
 
 import dummy_threading
 import fcntl
+import sys
+
 try:
 	import threading
 except ImportError:
 	import dummy_threading as threading
 
+import portage
 from portage import os
 from portage.exception import TryAgain
 from portage.locks import lockfile, unlockfile
 from _emerge.AbstractPollTask import AbstractPollTask
+from _emerge.AsynchronousTask import AsynchronousTask
 from _emerge.PollConstants import PollConstants
+from _emerge.SpawnProcess import SpawnProcess
+
+class AsynchronousLock(AsynchronousTask):
+	"""
+	This uses the portage.locks module to acquire a lock asynchronously,
+	using either a thread (if available) or a subprocess.
+	"""
+
+	__slots__ = ('path', 'scheduler',) + \
+		('_imp', '_force_async', '_force_dummy', '_force_process', \
+		'_force_thread')
+
+	def _start(self):
+
+		if not self._force_async:
+			try:
+				self._imp = lockfile(self.path,
+					wantnewlockfile=True, flags=os.O_NONBLOCK)
+			except TryAgain:
+				pass
+			else:
+				self.returncode = os.EX_OK
+				self.wait()
+				return
+
+		if self._force_process or \
+			(not self._force_thread and threading is dummy_threading):
+			self._imp = _LockProcess(path=self.path, scheduler=self.scheduler)
+		else:
+			self._imp = _LockThread(path=self.path,
+				scheduler=self.scheduler,
+				_force_dummy=self._force_dummy)
+
+		self._imp.addExitListener(self._imp_exit)
+		self._imp.start()
+
+	def _imp_exit(self, imp):
+		# call exit listeners
+		self.wait()
+
+	def _wait(self):
+		if self.returncode is not None:
+			return self.returncode
+		self.returncode = self._imp._wait()
+		return self.returncode
+
+	def unlock(self):
+		if self._imp is None:
+			raise AssertionError('not locked')
+		if isinstance(self._imp, (_LockProcess, _LockThread)):
+			self._imp.unlock()
+		else:
+			unlockfile(self._imp)
+		self._imp = None
 
-class AsynchronousLock(AbstractPollTask):
+class _LockThread(AbstractPollTask):
 	"""
 	This uses the portage.locks module to acquire a lock asynchronously,
 	using a background thread. After the lock is acquired, the thread
@@ -27,25 +85,10 @@ class AsynchronousLock(AbstractPollTask):
 	"""
 
 	__slots__ = ('lock_obj', 'path',) + \
-		('_files', '_force_thread', '_force_dummy',
+		('_files', '_force_dummy',
 		'_thread', '_reg_id',)
 
 	def _start(self):
-
-		if self._force_thread:
-			self._start_thread()
-			return
-
-		try:
-			self.lock_obj = lockfile(self.path,
-				wantnewlockfile=True, flags=os.O_NONBLOCK)
-		except TryAgain:
-			self._start_thread()
-		else:
-			self.returncode = os.EX_OK
-			self.wait()
-
-	def _start_thread(self):
 		pr, pw = os.pipe()
 		self._files = {}
 		self._files['pipe_read'] = os.fdopen(pr, 'rb', 0)
@@ -101,3 +144,81 @@ class AsynchronousLock(AbstractPollTask):
 			for f in self._files.values():
 				f.close()
 			self._files = None
+
+class _LockProcess(AbstractPollTask):
+	"""
+	This uses the portage.locks module to acquire a lock asynchronously,
+	using a subprocess. After the lock is acquired, the process
+	writes to a pipe in order to notify a poll loop running in the main
+	process. The unlock() method notifies the subprocess to release the
+	lock and exit.
+	"""
+
+	__slots__ = ('path', 'scheduler',) + \
+		('_proc', '_files', '_reg_id')
+
+	def _start(self):
+		in_pr, in_pw = os.pipe()
+		out_pr, out_pw = os.pipe()
+		self._files = {}
+		self._files['pipe_in'] = os.fdopen(in_pr, 'rb', 0)
+		self._files['pipe_out'] = os.fdopen(out_pw, 'wb', 0)
+		fcntl.fcntl(in_pr, fcntl.F_SETFL,
+			fcntl.fcntl(in_pr, fcntl.F_GETFL) | os.O_NONBLOCK)
+		self._reg_id = self.scheduler.register(in_pr,
+			PollConstants.POLLIN, self._output_handler)
+		self._registered = True
+		self._proc = SpawnProcess(
+			args=[portage._python_interpreter,
+				os.path.join(portage._bin_path, 'lock-helper.py'), self.path],
+				env=os.environ,
+				fd_pipes={0:out_pr, 1:in_pw, 2:sys.stderr.fileno()},
+				scheduler=self.scheduler)
+		self._proc.addExitListener(self._proc_exit)
+		self._proc.start()
+		os.close(out_pr)
+		os.close(in_pw)
+
+	def _proc_exit(self, proc):
+		if proc.returncode != os.EX_OK:
+			# There's no good reason for locks to fail.
+			raise AssertionError('lock process failed with returncode %s' \
+				% (proc.returncode,))
+
+	def _wait(self):
+		if self.returncode is not None:
+			return self.returncode
+		if self._registered:
+			self.scheduler.schedule(self._reg_id)
+		return self.returncode
+
+	def _output_handler(self, f, event):
+		buf = self._read_buf(self._files['pipe_in'], event)
+		if buf:
+			self._unregister()
+			self.returncode = os.EX_OK
+			self.wait()
+
+	def _unregister(self):
+		self._registered = False
+
+		if self._reg_id is not None:
+			self.scheduler.unregister(self._reg_id)
+			self._reg_id = None
+
+		if self._files is not None:
+			try:
+				pipe_in = self._files.pop('pipe_in')
+			except KeyError:
+				pass
+			else:
+				pipe_in.close()
+
+	def unlock(self):
+		if self._proc is None:
+			raise AssertionError('not locked')
+		self._files['pipe_out'].write(b'\0')
+		self._files['pipe_out'].close()
+		self._files = None
+		self._proc.wait()
+		self._proc = None