_BinpkgFetcherProcess: fix async_lock event loop recursion (bug 711178)

Make the async_lock method use the AsynchronousLock async_start
method in order to avoid event loop recursion.

Fixes: 5c40c3e ("SpawnProcess: use async_start method (bug 709746)")
Bug: https://bugs.gentoo.org/711178
Signed-off-by: Zac Medico <zmedico@gentoo.org>

lib/_emerge/BinpkgFetcher.py

@@ -16,6 +16,7 @@
 from portage import os
 from portage.util._async.AsyncTaskFuture import AsyncTaskFuture
 from portage.util._pty import _create_pty_or_pipe
+from portage.util.futures import asyncio
 from portage.util.futures.compat_coroutine import coroutine
 
 if sys.hexversion >= 0x3000000:
@@ -205,6 +206,7 @@ def sync_timestamp(self):
 								except OSError:
 									pass
 
+	@coroutine
 	def async_lock(self):
 		"""
 		This raises an AlreadyLocked exception if lock() is called
@@ -215,22 +217,22 @@ def async_lock(self):
 		if self._lock_obj is not None:
 			raise self.AlreadyLocked((self._lock_obj,))
 
-		result = self.scheduler.create_future()
-
-		def acquired_lock(async_lock):
-			if async_lock.wait() == os.EX_OK:
-				self.locked = True
-				result.set_result(None)
-			else:
-				result.set_exception(AssertionError(
-					"AsynchronousLock failed with returncode %s"
-					% (async_lock.returncode,)))
-
-		self._lock_obj = AsynchronousLock(path=self.pkg_path,
+		async_lock = self._lock_obj = AsynchronousLock(path=self.pkg_path,
 			scheduler=self.scheduler)
-		self._lock_obj.addExitListener(acquired_lock)
-		self._lock_obj.start()
-		return result
+		try:
+			yield async_lock.async_start()
+			yield async_lock.async_wait()
+		except asyncio.CancelledError:
+			if async_lock.poll() is None:
+				async_lock.cancel()
+			raise
+
+		if async_lock.returncode != os.EX_OK:
+			raise AssertionError(
+				"AsynchronousLock failed with returncode %s"
+				% (async_lock.returncode,))
+
+		self.locked = True
 
 	class AlreadyLocked(portage.exception.PortageException):
 		pass