问题描述
假设我在文件function.c中定义了一个函数，在main.c中创建了多个pthread来执行function.c中的函数
Suppose I defined a function in file function.c, and in main.c I create multiple pthreads to execute the function in function.c.
如果在function.c中，我定义了一个全局变量，例如int foo;
If in function.c, I define a global variable, for example, int foo;
那么，我的问题是，是每个线程都有自己的这个变量foo"的实例还是共享一个foo"?
Then, my question is, does every thread has its own instance of this variable "foo" or do they share a single "foo"?
推荐答案
它们共享一个 foo 变量.全局变量总是每个进程只存在一次，并且通常由互斥锁保护以避免并发访问.
They share a single foo variable. Global variable always exists only once per process and is usually protected by mutex to avoid concurrent access.
从 C11 开始，您可以使用 thread_local 将变量声明为每个线程的本地变量:
Since C11 you can use thread_local to declare the variable as local per thread:
#include <threads.h>
...
thread_local int perThreadInt;
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