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cmultithreadingthread-safetyposixshared-libraries
IWill80
IWill80

Reputation: 97

Thread safety clarification in a c library

Can someone clarify to me if the following piece of code is thread safety?

int get_time(uint64_t *time)
{
    struct timespec spec;
    if (!time)
        return -EFAULT;
    if (clock_gettime(CLOCK_REALTIME, &spec) == -1)
        return -errno;
    *time = //convert timespec into nanoseconds
    return SUCCESS;
}

This is an API in a library that could be called by multiple threads. The spec is a local variable so it not should be a problem. Correct? My doubt is about the clock_getime (POSIX.1-2001) and the assignment to the time argument. I would to introduce a mutex, but I'm not sure if it is strictly required.

Upvotes: 3

Views: 2245

Answers (1)

Deduplicator
Deduplicator

Reputation: 45654

You aren't using anything but automatic variables in your code, and the only function-call (clock_gettime) is inherently thread-safe, so the answer is:

Yes, it's safe.

From the POSIX spec:

3.396 Thread-Safe

A function that may be safely invoked concurrently by multiple threads. Each function defined in the System Interfaces volume of IEEE Std 1003.1-2001 is thread-safe unless explicitly stated otherwise. Examples are any "pure" function, a function which holds a mutex locked while it is accessing static storage, or objects shared among threads.

There is no exception listed on the spec for that function:
http://pubs.opengroup.org/onlinepubs/009695399/functions/clock_getres.html

Upvotes: 8

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