From 5d6fb8ebe497b63ffbd8df0434f943f18ecf472d Mon Sep 17 00:00:00 2001
From: Michael Hanselmann <hansmi@google.com>
Date: Fri, 8 Aug 2008 10:03:27 +0000
Subject: [PATCH] jstore: Change to not always require a lock
This way we can do locking when both noded and masterd are running
on the same machine, the latter holding an exclusive lock on the
queue.
Reviewed-by: iustinp
---
lib/jqueue.py | 2 +-
lib/jstore.py | 68 ++++++++++++++++++++++++++++-----------------------
2 files changed, 38 insertions(+), 32 deletions(-)
diff --git a/lib/jqueue.py b/lib/jqueue.py
index 1fc2ca81e..8e43c903b 100644
--- a/lib/jqueue.py
+++ b/lib/jqueue.py
@@ -283,7 +283,7 @@ class JobQueue(object):
self.release = self._lock.release
# Initialize
- self._queue_lock = jstore.InitAndVerifyQueue(exclusive=True)
+ self._queue_lock = jstore.InitAndVerifyQueue(must_lock=True)
# Read serial file
self._last_serial = jstore.ReadSerial()
diff --git a/lib/jstore.py b/lib/jstore.py
index 5065e862e..7424b7b7f 100644
--- a/lib/jstore.py
+++ b/lib/jstore.py
@@ -69,14 +69,13 @@ def ReadVersion():
return _ReadNumericFile(constants.JOB_QUEUE_VERSION_FILE)
-def InitAndVerifyQueue(exclusive):
+def InitAndVerifyQueue(must_lock):
"""Open and lock job queue.
If necessary, the queue is automatically initialized.
- @type exclusive: bool
- @param exclusive: Whether to lock the queue in exclusive mode. Shared
- mode otherwise.
+ @type must_lock: bool
+ @param must_lock: Whether an exclusive lock must be held.
@rtype: utils.FileLock
@return: Lock object for the queue. This can be used to change the
locking mode.
@@ -93,40 +92,47 @@ def InitAndVerifyQueue(exclusive):
# Lock queue
queue_lock = utils.FileLock(constants.JOB_QUEUE_LOCK_FILE)
try:
- # Determine locking function and call it
- if exclusive:
- fn = queue_lock.Exclusive
+ # The queue needs to be locked in exclusive mode to write to the serial and
+ # version files.
+ if must_lock:
+ queue_lock.Exclusive(blocking=True)
+ holding_lock = True
else:
- fn = queue_lock.Shared
-
- fn(blocking=False)
-
- # Verify version
- version = ReadVersion()
- if version is None:
- # Write new version file
- utils.WriteFile(constants.JOB_QUEUE_VERSION_FILE,
- data="%s\n" % constants.JOB_QUEUE_VERSION)
-
- # Read again
+ try:
+ queue_lock.Exclusive(blocking=False)
+ holding_lock = True
+ except errors.LockError:
+ # Ignore errors and assume the process keeping the lock checked
+ # everything.
+ holding_lock = False
+
+ if holding_lock:
+ # Verify version
version = ReadVersion()
+ if version is None:
+ # Write new version file
+ utils.WriteFile(constants.JOB_QUEUE_VERSION_FILE,
+ data="%s\n" % constants.JOB_QUEUE_VERSION)
- if version != constants.JOB_QUEUE_VERSION:
- raise errors.JobQueueError("Found job queue version %s, expected %s",
- version, constants.JOB_QUEUE_VERSION)
+ # Read again
+ version = ReadVersion()
- serial = ReadSerial()
- if serial is None:
- # Write new serial file
- utils.WriteFile(constants.JOB_QUEUE_SERIAL_FILE,
- data="%s\n" % 0)
+ if version != constants.JOB_QUEUE_VERSION:
+ raise errors.JobQueueError("Found job queue version %s, expected %s",
+ version, constants.JOB_QUEUE_VERSION)
- # Read again
serial = ReadSerial()
+ if serial is None:
+ # Write new serial file
+ utils.WriteFile(constants.JOB_QUEUE_SERIAL_FILE,
+ data="%s\n" % 0)
+
+ # Read again
+ serial = ReadSerial()
- if serial is None:
- # There must be a serious problem
- raise errors.JobQueueError("Can't read/parse the job queue serial file")
+ if serial is None:
+ # There must be a serious problem
+ raise errors.JobQueueError("Can't read/parse the job queue serial file")
except:
queue_lock.Close()
--
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