futex_wait - Wait on a futex.
#include <zircon/syscalls.h> zx_status_t zx_futex_wait(const zx_futex_t* value_ptr, int32_t current_value, zx_handle_t new_futex_owner, zx_time_t deadline);
futex_wait() atomically verifies that value_ptr still contains the value current_value and sleeps until the futex is made available by a call to zx_futex_wake
. Optionally, the thread can also be woken up after the deadline (with respect to ZX_CLOCK_MONOTONIC) passes.
A component that uses futexes should be prepared to handle spurious wakeups. A spurious wakeup is a situation where futex_wait() returns successfully even though the component did not wake the waiter by calling futex_wake().
Zircon's implementation of futexes currently does not generate spurious wakeups itself. However, commonly-used algorithms that use futexes can sometimes generate spurious wakeups. For example, the usual implementation of mutex_unlock
can potentially produce a futex_wake() call on a memory location after the location has been freed and reused for unrelated purposes.
A successful call to futex_wait() results in the owner of the futex being set to the thread referenced by the new_futex_owner
handle, or to nothing if new_futex_owner
is ZX_HANDLE_INVALID.
See Ownership and Priority Inheritance in futex for details.
None.
futex_wait() returns ZX_OK on success.
ZX_ERR_INVALID_ARGS One of the following is true:
value_ptr
is not a valid userspace pointervalue_ptr
is not aligned to a sizeof(zx_futex_t) boundary.new_futex_owner
is currently a member of the waiters for value_ptr.ZX_ERR_BAD_HANDLE new_futex_owner
is not ZX_HANDLE_INVALID, and not a valid handle. ZX_ERR_WRONG_TYPE new_futex_owner
is a valid handle, but is not a handle to a thread. ZX_ERR_BAD_STATE current_value
does not match the value at value_ptr
. ZX_ERR_TIMED_OUT The thread was not woken before deadline
passed.