thrd_success, thrd_timedout, thrd_busy, thrd_nomem, thrd_error

From cppreference.com
< c‎ | thread
Defined in header <threads.h>
enum {

    thrd_success = /* unspecified */,
    thrd_nomem = /* unspecified */,
    thrd_timedout = /* unspecified */,
    thrd_busy = /* unspecified */,
    thrd_error = /* unspecified */

};
(since C11)

Identifiers a thread error state.

Constant Explanation
thrd_success indicates successful return value
thrd_timedout indicates timed out return value
thrd_busy indicates unsuccessful return value due to resource temporary unavailable
thrd_nomem indicates unsuccessful return value due to out of memory condition
thrd_error indicates unsuccessful return value