Question

我在嵌套的Parallel.For循环（vb.net）中调用了一个子程序MyPartsMatrix。 MyPartsMatrix需要一个名为＆＃34;未填充的变量＆＃34;传递ByRef，因为此值在MyPartsMatrix子例程中被修改。我需要在子程序MyPartsMatrix执行后抓取并存储该值。

＆＃34;未填充＆＃34;当我运行此代码的并行版本而不是非并行版本时，使用常规嵌套For ... Next循环时，变量会产生不同的值。我无法弄清楚为什么会这样。

从Parallel.For循环内部调用另一个子程序是否可以安全线程？

这个变量＆＃34;未填充＆＃34;线程安全？

#
# Server-Pool Management (MPM specific)
# 

#
# PidFile: The file in which the server should record its process
# identification number when it starts.
#
# Note that this is the default PidFile for most MPMs.
#
<IfModule !mpm_netware_module>
    PidFile "logs/httpd.pid"
</IfModule>

#
# Only one of the below sections will be relevant on your
# installed httpd.  Use "apachectl -l" to find out the
# active mpm.
#

# prefork MPM
# StartServers: number of server processes to start
# MinSpareServers: minimum number of server processes which are kept spare
# MaxSpareServers: maximum number of server processes which are kept spare
# MaxRequestWorkers: maximum number of server processes allowed to start
# MaxConnectionsPerChild: maximum number of connections a server process serves
#                         before terminating
<IfModule mpm_prefork_module>
    StartServers             5
    MinSpareServers          5
    MaxSpareServers         10
    MaxRequestWorkers      150
    MaxConnectionsPerChild   0
</IfModule>

# worker MPM
# StartServers: initial number of server processes to start
# MinSpareThreads: minimum number of worker threads which are kept spare
# MaxSpareThreads: maximum number of worker threads which are kept spare
# ThreadsPerChild: constant number of worker threads in each server process
# MaxRequestWorkers: maximum number of worker threads
# MaxConnectionsPerChild: maximum number of connections a server process serves
#                         before terminating
<IfModule mpm_worker_module>
    StartServers             2
    ServerLimit        500
    MinSpareThreads         25
    MaxSpareThreads         75 
    ThreadsPerChild         25
    MaxRequestWorkers      150
    MaxConnectionsPerChild   0
</IfModule>

# event MPM
# StartServers: initial number of server processes to start
# MinSpareThreads: minimum number of worker threads which are kept spare
# MaxSpareThreads: maximum number of worker threads which are kept spare
# ThreadsPerChild: constant number of worker threads in each server process
# MaxRequestWorkers: maximum number of worker threads
# MaxConnectionsPerChild: maximum number of connections a server process serves
#                         before terminating
<IfModule mpm_event_module>
    StartServers             2
    MinSpareThreads         25
    MaxSpareThreads         75
    ThreadsPerChild         25
    MaxRequestWorkers      150
    MaxConnectionsPerChild   0
</IfModule>

# NetWare MPM
# ThreadStackSize: Stack size allocated for each worker thread
# StartThreads: Number of worker threads launched at server startup
# MinSpareThreads: Minimum number of idle threads, to handle request spikes
# MaxSpareThreads: Maximum number of idle threads
# MaxThreads: Maximum number of worker threads alive at the same time
# MaxConnectionsPerChild: Maximum  number of connections a thread serves. It
#                         is recommended that the default value of 0 be set
#                         for this directive on NetWare.  This will allow the
#                         thread to continue to service requests indefinitely.
<IfModule mpm_netware_module>
    ThreadStackSize      65536
    StartThreads           250
    MinSpareThreads         25
    MaxSpareThreads        250
    MaxThreads            1000
    MaxConnectionsPerChild   0
</IfModule>

# OS/2 MPM
# StartServers: Number of server processes to maintain
# MinSpareThreads: Minimum number of idle threads per process, 
#                  to handle request spikes
# MaxSpareThreads: Maximum number of idle threads per process
# MaxConnectionsPerChild: Maximum number of connections per server process
<IfModule mpm_mpmt_os2_module>
    StartServers             2
    MinSpareThreads          5
    MaxSpareThreads         10
    MaxConnectionsPerChild   0
</IfModule>

# WinNT MPM
# ThreadsPerChild: constant number of worker threads in the server process
# MaxConnectionsPerChild: maximum number of connections a server process serves
<IfModule mpm_winnt_module>
    ThreadsPerChild        1150
    MaxConnectionsPerChild   0
</IfModule>

# The maximum number of free Kbytes that every allocator is allowed
# to hold without calling free(). In threaded MPMs, every thread has its own
# allocator. When not set, or when set to zero, the threshold will be set to
# unlimited.
<IfModule !mpm_netware_module>
    MaxMemFree            2048
</IfModule>
<IfModule mpm_netware_module>
    MaxMemFree             100
</IfModule>

如果这不是线程安全的，是否有另一种方法来写这个，以便＆＃34;未填充＆＃34;变量是线程安全的还是调用另一个子例程线程安全吗？

Answer 1

如果没有MakeSchedule（你在其他地方称之为MyMakePartsMatrix）的定义，则无法确定它是否是线程安全的。

要成为线程安全，sub不需要修改未填充的任何内容。这将确保使用相同的输入多次调用它将始终产生相同的输出。我还建议转换为函数，因为我发现这更容易理解发生了什么。

另一方面说明：

如果你没有嵌套并行循环，你的表现会更好。在启动第二个循环之前，您当前正在等待内循环完成。如果你使用更大的x + y值，那么类似代码的东西会更好。

    Dim scenarios = From x2 In Enumerable.Range(0, x)
        From y2 In Enumerable.Range(0, y)
        Select New With {x2, y2}

    Parallel.ForEach(scenarios, Sub(s)

                                End Sub)

在Parallel.For中调用子程序（并将变量ByRef传递给它）线程安全吗？

1 个答案: