一个线程可以被pre抢占在系统调用之中内核？ [英] Can a thread be pre-empted in the midst of a system call to kernel?

问题描述

我运行2个线程（假设他们是暂时的pthreads）。 Thread_1（）使一个用户定义的API调用最终确实在内核一些工作。 Thread_2（）是完全在用户空间。

I'm running 2 threads ( assume they are pthreads for the moment) . Thread_1() makes a user-defined API call which ultimately does some work in the kernel . Thread_2() is totally in user-space.

我的问题是：能否Thread_2（）开始，而API调用过程中，控制地方在内核中由pre-先发制人Thread_1（）执行？如果不是，为什么，如果我想发生这种情况（因任何理由），我有什么做的？

My question is : Can Thread_2() start executing by pre-empting Thread_1() while the API call is in progress , the control is somewhere inside the kernel ? If not , why , and if I want this scenario to occur ( for any reasons ) , what do I have to do ?

推荐答案

如果你问是否像阻塞内核调用一个 FREAD（）要求磁盘IO可pre抢占，那么是的。

If you are asking whether a blocking kernel call like an fread() which requires disk IO can be pre-empted, then yes.

更具体地说阻塞调用将基本上把Thread_1等待不管它在等待入睡。如果Thread_1是睡着了，然后Thread_2将被安排运行（除非有更高优先级的等待运行的东西）。

More specifically a blocking call will basically put Thread_1 to sleep while waiting for whatever it's waiting for. If Thread_1 is asleep then Thread_2 will be scheduled to run (unless there's something of higher priority waiting to run).

编辑：如果您希望的方式是相当有信心的Thread_1正在执行阻塞调用，使Thread_2优先级低于Thread_1（因此一般的不运行，除非Thread_1被阻塞），它运行时，它提升它的优先级比Thread_1一个更高的水平，直到硬件中断已交付使用，此时它降低其优先级和呼叫 SCHED_YIELD（）。

If you want a way to be "fairly confident" that Thread_1 is performing a blocking call, make Thread_2 lower priority than Thread_1 (so that it generally doesn't run unless Thread_1 is blocked) and when it runs, it elevates its priority to a higher level than Thread_1 until the hardware interrupt has been delivered, at which point it lowers its priority and calls sched_yield().

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