Question

http://www.cs.colostate.edu/~cs370/Spring15/Workbook/thread_ex.txt

我的教授提供了上面的示例代码（不重复以保留他的IP），并且我对输出感到困惑。

有两个函数用作启动例程，T1和T2，并且有两个单独的for循环启动新线程。每个线程都有一个tid，应该在创建线程时匹配t的值，但是有几个相同函数的线程具有相同的tid，如他的示例输出结尾所示，即有两个T1线程与tid 1.为什么会发生这种情况？如果有4个T1线程，那么它是否应该生成0-3？

Answer 1

您的教授设计错误，t在主线程中更改其值，并且在不使用互斥的情况下由其他线程访问。

这里有clang的TSan所说的话：

==================
WARNING: ThreadSanitizer: data race (pid=5810)
  Read of size 4 at 0x7fff193c03e4 by thread T1:
    #0 T1(void*) /home/brian/src/so/threading/ex.cpp:16 (exe+0x0000000a0497)

  Previous write of size 4 at 0x7fff193c03e4 by main thread:
    #0 main /home/brian/src/so/threading/ex.cpp:61 (exe+0x0000000a0881)

  Location is stack of main thread.

  Thread T1 (tid=5812, running) created by main thread at:
    #0 pthread_create ??:0 (exe+0x000000045a8b)
    #1 main /home/brian/src/so/threading/ex.cpp:62 (exe+0x0000000a085a)

SUMMARY: ThreadSanitizer: data race /home/brian/src/so/threading/ex.cpp:16 T1(void*)
==================

......接着......

T1 [0] count = 12
==================
WARNING: ThreadSanitizer: data race (pid=5810)
  Write of size 1 at 0x7ff2f8aa2c80 by main thread:
    #0 main /home/brian/src/so/threading/ex.cpp:70 (exe+0x0000000a0964)

  Previous read of size 1 at 0x7ff2f8aa2c80 by thread T1:
    #0 T1(void*) /home/brian/src/so/threading/ex.cpp:18 (exe+0x0000000a04de)

  As if synchronized via sleep:
    #0 sleep ??:0 (exe+0x00000003f7bd)
    #1 main /home/brian/src/so/threading/ex.cpp:69 (exe+0x0000000a0952)

  Thread T1 (tid=5812, running) created by main thread at:
    #0 pthread_create ??:0 (exe+0x000000045a8b)
    #1 main /home/brian/src/so/threading/ex.cpp:62 (exe+0x0000000a085a)

SUMMARY: ThreadSanitizer: data race /home/brian/src/so/threading/ex.cpp:70 main
==================
T1 thread 1 done.

为什么多个线程得到相同的“tid？”

1 个答案: