Reads the eventfd counter or wait if it is zero.
ssize_t eventfd_ctx_read(struct eventfd_ctx * ctx, int no_wait, __u64 * cnt);
ctx
[in] Pointer to eventfd context.
no_wait
[in] Different from zero if the operation should not block.
cnt
[out] Pointer to the 64-bit counter value.
Returns 0 if successful, or the following error codes:
-EAGAIN : The operation would have blocked but no_wait was non-zero. -ERESTARTSYS : A signal interrupted the wait operation.
If no_wait is zero, the function might sleep until the eventfd internal counter becomes greater than zero.