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Use FIFO for storage locking

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This prevents starvation of writers in the current process
This commit is contained in:
Unrud 2016-05-22 22:30:46 +02:00
parent 1ea9a33101
commit 14daa88772
1 changed files with 15 additions and 4 deletions
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19
radicale/storage.py
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@ -524,7 +524,8 @@ class Collection(BaseCollection):
return "".join([item.serialize() for item in items]) return "".join([item.serialize() for item in items])
return "" return ""
_lock = threading.Condition() _lock = threading.Lock()
_waiters = []
_lock_file = None _lock_file = None
_lock_file_locked = False _lock_file_locked = False
_readers = 0 _readers = 0
@ -544,11 +545,20 @@ class Collection(BaseCollection):
# Use a primitive lock which only works within one process as a # Use a primitive lock which only works within one process as a
# precondition for inter-process file-based locking # precondition for inter-process file-based locking
with cls._lock: with cls._lock:
cls._lock.wait_for(condition) if cls._waiters or not condition():
# use FIFO for access requests
waiter = threading.Condition(lock=cls._lock)
cls._waiters.append(waiter)
while True:
waiter.wait()
if condition():
break
cls._waiters.pop(0)
if mode == "r": if mode == "r":
cls._readers += 1 cls._readers += 1
# notify additional potential readers # notify additional potential readers
cls._lock.notify() if cls._waiters:
cls._waiters[0].notify()
else: else:
cls._writer = True cls._writer = True
if not cls._lock_file: if not cls._lock_file:
@ -596,4 +606,5 @@ class Collection(BaseCollection):
except OSError: except OSError:
cls.logger.debug("Unlocking not supported") cls.logger.debug("Unlocking not supported")
cls._lock_file_locked = False cls._lock_file_locked = False
cls._lock.notify() if cls._waiters:
cls._waiters[0].notify()