Multi-process + Semaphore semaphore, process signal Semaphore

Multi-process + Semaphore semaphore, process signal Semaphore

The following is an example.

from multiprocessing import Processfrom multiprocessing import Semaphoreimport datetimeimport timeimport multiprocessingdef worker(s, i):    s.acquire()    print(multiprocessing.current_process().name + " acquire",datetime.datetime.now())    time.sleep(i)    print(multiprocessing.current_process().name + " release",datetime.datetime.now(),"\n")    s.release()if __name__ == "__main__":    s = multiprocessing.Semaphore(2)    for i in range(5):        p = multiprocessing.Process(target = worker, args=(s, i*2))        p.start()

Running result:

Analysis: p = multiprocessing. Process (......) Five processes and five p. start processes are defined in parallel. The result is that the semaphore restricts the process's access to critical resources. S = multiprocessing. semaphore (2) defines the maximum Semaphore value 2, release: + 1 acquire:-step 1, five processes run concurrently, process 1 executes and waits for 0 s, s-1 = 1 second step, five processes run concurrently, process 2 execution and wait 2 s, S-1 = 0 third step, because process 1 is executed, and the wait time is 0, process 2 needs to wait 2 s. Therefore, this step must be executed by process 1, and the execution of process 1 is completed, while the semaphore + 1 is not blocked. Step 4, process 2 enters wait 2 s, so only three processes 3, 4, 5 parallel, process 4 Execution and wait 6 s, S-1 = fifth step, process 2 waits for 2 seconds to complete, process 2 executes, S + 1 = 1 step 6, process 4 waits, only two processes 3 and 5 are in parallel, process 3 executes and waits for 4 seconds, s-1 = Step 7, process 3 and 4 wait for time to end at the same time, process 3 compete for and critical resource execution, S + 1 = Step 8, process 4 wait, process 5 Execution and wait 8 s, S-1 = 0 ninth step, process 4 Execution, S + 1 = step 10, process 5 Execution, S + 1 = 1 Reference: http://www.cnblogs.com/kaituorensheng/p/4445418.html