Reads the eventfd counter or wait if it is zero.
ssize_t eventfd_ctx_read (
|struct eventfd_ctx * ctx, |
| ||int no_wait, |
| ||__u64 * cnt|
[in] Pointer to eventfd context.
[in] Different from zero if the operation should not block.
[out] Pointer to the 64-bit counter value.
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.
no_wait is zero, the function might sleep until the eventfd internal
counter becomes greater than zero.