问题描述
我很想知道如何在Unix内部实现与线程之间的同步相关的功能.例如，当我呼叫pthread_mutex_lock时会发生什么?有没有使用中的指针?引用源代码确实有帮助.
I am just curious to know how functions related to synchronization between threads are implemented inside Unix. For example, what happens when I call pthread_mutex_lock? Are there any pointers in use? A reference to the source code would really help.
推荐答案
它既复杂又因Unix与Unix的不同而不同.
It is both complicated and differs from Unix to Unix variant.
例如，在Linux中，使用了称为Futex(快速用户空间互斥锁的简称)的系统.
In Linux, for example, a system called Futex (Short for Fast Userspace Mutex) is used.
在此系统中，对用户空间中的互斥变量执行原子增量和测试操作.
In this system an atomic increment and test operation is performed on the mutex variable in user space.
如果操作结果表明锁上没有争用，则对pthread_mutex_lock的调用将返回，而无需将上下文切换到内核中，因此获取互斥量的操作可以非常快.
If the result of the operation indicates that there was no contention on the lock, the call to pthread_mutex_lock returns without ever context switching into the kernel, so the operation of taking a mutex can be very fast.
仅当检测到争用时，系统调用(称为futex)才会发生，并且上下文切换到内核中，这会使调用进程进入睡眠状态，直到释放互斥锁为止.
Only if contention was detected does a system call (called futex) and context switch into the kernel occurs that puts the calling process to sleep until the mutex is released.
还有很多更多的细节，尤其是对于可靠和/或优先级继承互斥，但这就是它的本质.
There are many many more details, especially for reliable and/or priority inhertience mutexes, but this is the essence of it.
有关更多详细信息，请参见: http://linux.die.net/man/2/futex 和 http://en.wikipedia.org/wiki/Futex
For more details see: http://linux.die.net/man/2/futex and http://en.wikipedia.org/wiki/Futex
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