import threading
import weakref
_mainlock = threading.RLock()
_job_locks = weakref.WeakValueDictionary()
def do_thing(job_id):
_mainlock.acquire() #Dictionary modification lock acquire
_job_locks.setdefault(job_id, threading.RLock()) #Possibly modifies the dictionary
_mainlock.release()
_job_locks[job_id].acquire()
try:
one_time_init(job_id)
finally:
_job_locks[job_id].release()
#On function return, the weakref.WeakValueDictionary should cause the key to evaporate
假设 do_thing() 在许多 id 编号可能相同也可能不同的线程上被多次调用(例如,4 次 ID 为 3,各有一次 ID 不同),这个线程安全吗?one_time_init() 是否会一次针对特定的作业 ID 运行多次?(PS:one_time_init 保存每个 ID 运行一次的状态,因此如果它已经运行完成,则调用它是无操作的)
更新代码(感谢 THC4k):
import threading
import weakref
_mainlock = threading.RLock()
_job_locks = weakref.WeakValueDictionary()
def do_thing(job_id):
with _mainlock:
jl = _job_locks.setdefault(job_id, threading.RLock())
with jl:
one_time_init(job_id)