Python多处理问题/误解

Question

我遇到了多处理问题;我在Linux 2.6.36上使用python2.7。我知道使用更高级别的模块或库会更容易，但我试图使用较低级别的函数（os.fork（）和os.exec *）来确保我真正理解 - 这是一种学习练习。

下面是我的代码，它是一个多处理'ping'工具。这个问题似乎在运行，它会在os.wait（）行上每隔一段时间抛出一个OSError。 “没有子进程”

这对我没有意义，因为os.wait（）只应在程序捕获子进程已退出并需要获得的信号时调用。

以下代码是样本输出。

我在做什么错？

带有下列错误的示例输出-------------------------------------- -

[18188] 
[18188, 18189] 
[18188, 18189, 18190] 
[18188, 18189, 18190, 18191] 
[18188, 18189, 18190, 18191, 18192] 
[18188, 18189, 18190, 18191, 18192, 18193] 
[18188, 18189, 18190, 18191, 18192, 18193, 18194] 
[18188, 18189, 18190, 18191, 18192, 18193, 18194, 18195] 
[18188, 18189, 18191, 18192, 18193, 18194, 18195, 18196] 
[18188, 18191, 18192, 18193, 18194, 18195, 18196, 18197] 
[18188, 18191, 18192, 18194, 18195, 18196, 18197, 18198] 
[18191, 18192, 18194, 18195, 18196, 18197, 18198, 18201] 
[18191, 18194, 18195, 18196, 18197, 18198, 18201, 18202] 
[18191, 18195, 18196, 18197, 18198, 18201, 18202, 18203] 
[18195, 18196, 18197, 18198, 18201, 18202, 18203, 18204] 
[18196, 18197, 18198, 18202, 18203, 18204, 18205] 
[18196, 18197, 18198, 18202, 18203, 18204, 18205, 18206] 
[18197, 18198, 18202, 18203, 18204, 18205, 18206, 18207] 
[18198, 18203, 18204, 18205, 18206, 18207, 18210] 
[18198, 18203, 18204, 18205, 18206, 18207, 18210, 18211] 
Traceback (most recent call last): 
    File "./sunmon-mp", line 33, in <module> 
    pid = os.fork() 
    File "./sunmon-mp", line 12, in chldClean 
    pid, status = os.wait() 
OSError: [Errno 10] No child processes 
[18203, 18204, 18205, 18206, 18207, 18210, 18211, 18212] 
[18203, 18204, 18206, 18207, 18210, 18211, 18212, 18213] 
[18203, 18204, 18206, 18207, 18211, 18212, 18213, 18214] 
[18203, 18204, 18206, 18207, 18211, 18212, 18214, 18215] 
[18203, 18204, 18206, 18207, 18212, 18214, 18215, 18217] 
[18203, 18204, 18206, 18207, 18214, 18215, 18217, 18218] 
[18203, 18204, 18206, 18207, 18215, 18217, 18218, 18219] 
[18204, 18206, 18207, 18215, 18217, 18218, 18219, 18220] 
[18204, 18206, 18207, 18217, 18218, 18219, 18220, 18221] 
[18206, 18207, 18217, 18218, 18219, 18220, 18221, 18223] 
[18207, 18217, 18218, 18219, 18220, 18221, 18223, 18224] 
[18217, 18218, 18219, 18220, 18221, 18223, 18224, 18225] 
[18217, 18219, 18220, 18221, 18223, 18224, 18225, 18226] 
[18217, 18219, 18220, 18221, 18223, 18225, 18226, 18227] 
[18217, 18219, 18220, 18221, 18223, 18226, 18227, 18228] 
[18217, 18220, 18221, 18223, 18226, 18227, 18228, 18229] 
[18217, 18220, 18221, 18223, 18227, 18228, 18229, 18230] 
[18217, 18220, 18221, 18223, 18227, 18228, 18230, 18231] 
[18220, 18221, 18223, 18227, 18228, 18230, 18231, 18233] 
[18221, 18223, 18227, 18228, 18230, 18231, 18233, 18234] 
[18223, 18227, 18228, 18230, 18231, 18233, 18234, 18235] 
[18223, 18227, 18228, 18231, 18233, 18234, 18235, 18236] 
[18223, 18227, 18228, 18231, 18233, 18234, 18236, 18237] 
[18223, 18227, 18228, 18231, 18233, 18234, 18237, 18239] 
[18227, 18228, 18231, 18233, 18234, 18237, 18239, 18240] 
[18228, 18231, 18233, 18234, 18237, 18239, 18240, 18241] 
[18228, 18231, 18233, 18237, 18239, 18240, 18241, 18242] 
[18231, 18233, 18237, 18239, 18240, 18241, 18242, 18243] 
[18231, 18233, 18239, 18240, 18241, 18242, 18243, 18244] 
[18231, 18233, 18239, 18240, 18242, 18243, 18244, 18245] 
[18231, 18233, 18239, 18242, 18243, 18244, 18245, 18246] 
[18231, 18233, 18242, 18243, 18244, 18245, 18246, 18247] 
[18233, 18242, 18243, 18244, 18245, 18246, 18247, 18248] 
[18242, 18243, 18244, 18245, 18246, 18247, 18248, 18249] 
[18243, 18244, 18245, 18246, 18247, 18248, 18249, 18250] 
[18243, 18245, 18246, 18247, 18248, 18249, 18250, 18251] 
[18243, 18245, 18247, 18248, 18249, 18250, 18251, 18252] 
[18243, 18245, 18248, 18249, 18250, 18251, 18252, 18253] 
[18243, 18245, 18249, 18250, 18251, 18252, 18253, 18254] 
[18243, 18245, 18249, 18250, 18252, 18253, 18254, 18255] 
[18245, 18249, 18250, 18252, 18253, 18254, 18255, 18258] 
[18249, 18250, 18252, 18253, 18254, 18255, 18258, 18259] 
[18249, 18250, 18253, 18254, 18255, 18258, 18259, 18260] 
[18249, 18250, 18253, 18254, 18255, 18258, 18260, 18261] 
[18249, 18250, 18253, 18254, 18255, 18260, 18261, 18262] 
[18250, 18253, 18254, 18255, 18260, 18261, 18262, 18263] 
[18253, 18254, 18255, 18260, 18261, 18262, 18263, 18264] 
[18253, 18254, 18255, 18261, 18262, 18263, 18264, 18265] 
[18253, 18254, 18255, 18261, 18262, 18264, 18265, 18266] 
[18254, 18255, 18261, 18262, 18264, 18265, 18266, 18267] 
[18255, 18261, 18262, 18264, 18265, 18266, 18267, 18268] 
[18261, 18262, 18264, 18265, 18266, 18267, 18268, 18269] 
[18261, 18262, 18265, 18266, 18267, 18268, 18269, 18270] 
[18261, 18262, 18265, 18266, 18267, 18268, 18270, 18271] 
[18261, 18262, 18265, 18266, 18267, 18270, 18271, 18273] 
[18261, 18262, 18265, 18266, 18270, 18271, 18273, 18274] 
[18261, 18262, 18265, 18266, 18271, 18273, 18274, 18275] 
[18261, 18262, 18265, 18266, 18271, 18273, 18275, 18276] 
[18262, 18265, 18266, 18271, 18273, 18275, 18276, 18277] 
[18262, 18265, 18266, 18273, 18275, 18276, 18277, 18278] 
[18265, 18266, 18273, 18276, 18277, 18278, 18280] 
[18265, 18266, 18273, 18276, 18277, 18278, 18280, 18281] 
Traceback (most recent call last): 
    File "./sunmon-mp", line 33, in <module> 
    pid = os.fork() 
    File "./sunmon-mp", line 12, in chldClean 
    pid, status = os.wait() 
OSError: [Errno 10] No child processes 
[18265, 18273, 18276, 18277, 18278, 18280, 18282] 
[18265, 18276, 18277, 18278, 18280, 18281, 18282, 18283] 
[18265, 18276, 18278, 18281, 18282, 18283, 18284] 
[18265, 18276, 18278, 18281, 18282, 18283, 18284, 18285] 
[18265, 18276, 18278, 18282, 18283, 18284, 18285, 18286] 
[18265, 18276, 18278, 18283, 18284, 18286, 18289] 
[18265, 18276, 18278, 18283, 18284, 18286, 18289, 18290] 
Traceback (most recent call last): 
    File "./sunmon-mp", line 33, in <module> 
    pid = os.fork() 
    File "./sunmon-mp", line 12, in chldClean 
    pid, status = os.wait() 
OSError: [Errno 10] No child processes 
[18265, 18276, 18278, 18283, 18284, 18289, 18290, 18291] 
[18276, 18278, 18283, 18284, 18289, 18290, 18291, 18292] 
[18276, 18278, 18283, 18284, 18290, 18291, 18292, 18293] 
[18276, 18278, 18283, 18284, 18290, 18291, 18293, 18294] 
[18276, 18278, 18283, 18284, 18290, 18291, 18294, 18295] 
[18278, 18283, 18284, 18290, 18291, 18294, 18295, 18297] 
[18283, 18284, 18290, 18291, 18294, 18295, 18297, 18298] 
[18283, 18284, 18290, 18291, 18295, 18297, 18298, 18299] 

Answer 1

也许你受到bug causing child processes to inherit pending signals的影响。这可以解释为什么堆栈跟踪出现多次。孩子正试图等待自己不存在的孩子。

也可以同时处理多个相同类型的排队信号，所以我不建议在信号处理程序中使用wait（）。

Answer 2

您可能会遇到与this SO question中描述的相同的竞态条件问题。不幸的是，我现在无法测试你的代码（Windows环境，所以没有SIGCHLD），但似乎如果你在问题行12上使用os.waitpid(-1, os.WNOHANG)，你不会得到错误。不过，您仍然无法保证您不会遇到上述竞争条件。