Wait for signals on an object.


#include <zircon/syscalls.h>

zx_status_t zx_object_wait_one(zx_handle_t handle,
                               zx_signals_t signals,
                               zx_time_t deadline,
                               zx_signals_t* observed);


zx_object_wait_one() is a blocking syscall that causes the caller to wait until either the deadline passes or the object to which handle refers asserts at least one signal specified by the bitmask signals. If the object is already asserting at least one of the specified signals, the wait ends immediately with ZX_OK.

Upon return, if non-NULL, observed is a bitmap of all of the signals asserted on the object. If one of the specified signals was asserted, observed will be the set of signals asserted at the moment the specified signal was first asserted. Otherwise, if deadline passes or handle is closed, observed will contain the state of the object's signals at the time the zx_object_wait_one syscall completed.

The deadline parameter specifies a deadline with respect to ZX_CLOCK_MONOTONIC and will be automatically adjusted according to the job's timer slack policy.

  • ZX_TIME_INFINITE is a special value meaning wait forever.
  • 0 (or any value before the current time in ZX_CLOCK_MONOTONIC) will query the current value of the signal(s).


handle must have ZX_RIGHT_WAIT.


zx_object_wait_one() returns ZX_OK if any of signals were active when the call was made, or observed on the object before deadline passes.

In the event of ZX_ERR_TIMED_OUT, observed may reflect state changes that occurred after the deadline passed, but before the syscall returned.

In the event of ZX_ERR_CANCELED, handle has been closed, and observed will have the ZX_SIGNAL_HANDLE_CLOSED bit set.

For any other return value, observed is undefined.


ZX_ERR_INVALID_ARGS observed is an invalid pointer.

ZX_ERR_BAD_HANDLE handle is not a valid handle.

ZX_ERR_ACCESS_DENIED handle does not have ZX_RIGHT_WAIT and may not be waited upon.

ZX_ERR_CANCELED handle was invalidated (e.g., closed) during the wait.

ZX_ERR_TIMED_OUT The specified deadline passed before any of the specified signals are observed on handle.

ZX_ERR_NOT_SUPPORTED handle is a handle that cannot be waited on (for example, a Port handle).


See signals for more information about signals and their terminology.