当前代码为:
def export_data(file): <runs the db2 database command to export tables to file> def export_to_files(yaml): logger = logging.getLogger("export_to_files") thread1 = threading.Thread(target=export_data, args=[out_file1]) thread1.start() thread2 = threading.Thread(target=export_data, args=[out_file2]) thread2.start() thread1.join() thread2.join() def main(): export_to_files() if __name__ == "__main__": main()我的理解是join()仅阻止调用线程.但是,我没有意识到thread1.join()甚至会阻止thread2的执行,实际上使代码只能运行1个线程,即thread1.
My understanding was that join() only blocks the calling thread. However, I did not realize that thread1.join() would even block thread2 from executing, essentially making the code to only run 1 thread i.e. thread1.
我如何同时执行两个线程,同时让主线程等待两个线程完成?
How can I execute both the threads concurrently, while have the main thread wait for both to complete?
我纠正了,这2个线程确实在运行,但是似乎只有1个线程实际上在某个时间点正在做"事情.
I stand corrected, the 2 threads do run, but it seems like only 1 thread is actually "doing" things at a point in time.
为了进一步详细说明,callable_method正在从数据库读取数据并写入文件.现在我可以看到有2个文件正在更新(每个线程都写入一个单独的文件),但是其中一个文件已经有一段时间没有更新了,而另一个文件是最新的.
To elaborate further, the callable_method is reading data from the database and writing to a file. While I can now see 2 files being updated(each thread writes to a separate file), one of the files is not updated for quite some time now, while the other file is up-to-date as to current time.
没有没有连接对象.查询是从db2命令行界面运行的.
There is no connection object being used. The queries are run from the db2 command line interface.
推荐答案您可以使用很大程度上未记录在案的 ThreadPool multiprocessing.pool中的类,以按照以下方式进行操作:
You could use the largely undocumented ThreadPool class in multiprocessing.pool to do something along these lines:
from multiprocessing.pool import ThreadPool import random import threading import time MAX_THREADS = 2 print_lock = threading.Lock() def export_data(fileName): # simulate writing to file runtime = random.randint(1, 10) while runtime: with print_lock: # prevent overlapped printing print('[{:2d}] Writing to {}...'.format(runtime, fileName)) time.sleep(1) runtime -= 1 def export_to_files(filenames): pool = ThreadPool(processes=MAX_THREADS) pool.map_async(export_data, filenames) pool.close() pool.join() # block until all threads exit def main(): export_to_files(['out_file1', 'out_file2', 'out_file3']) if __name__ == "__main__": main()示例输出:
[ 9] Writing to out_file1... [ 6] Writing to out_file2... [ 5] Writing to out_file2... [ 8] Writing to out_file1... [ 4] Writing to out_file2... [ 7] Writing to out_file1... [ 3] Writing to out_file2... [ 6] Writing to out_file1... [ 2] Writing to out_file2... [ 5] Writing to out_file1... [ 1] Writing to out_file2... [ 4] Writing to out_file1... [ 8] Writing to out_file3... [ 3] Writing to out_file1... [ 7] Writing to out_file3... [ 2] Writing to out_file1... [ 6] Writing to out_file3... [ 1] Writing to out_file1... [ 5] Writing to out_file3... [ 4] Writing to out_file3... [ 3] Writing to out_file3... [ 2] Writing to out_file3... [ 1] Writing to out_file3...更多推荐
同时执行多个线程
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