mx_object_signal, mx_object_signal_peer


object_signal - signal an object

object_signal_peer - signal an object's peer


#include <magenta/syscalls.h>

mx_status_t mx_object_signal(mx_handle_t handle, uint32_t clear_mask, uint32_t set_mask);
mx_status_t mx_object_signal_peer(mx_handle_t handle, uint32_t clear_mask, uint32_t set_mask);


mx_object_signal() and mx_object_signal_peer() set and clear the userspace-accessible signal bits on an object or on the object's peer, respectively. A object peer is the opposite endpoint of a channel, socket, fifo, or eventpair.

Most of the 32 signals are reserved for system use and are assigned to per-object functions, like MX_CHANNEL_READABLE or MX_TASK_TERMINATED. 8 signals are available for userspace processes to use as they see fit: MX_USER_SIGNAL_0 through MX_USER_SIGNAL_7.

Event objects also allow control over the MX_EVENT_SIGNALED bit.

Eventpair objects also allow control over the MX_EPAIR_SIGNALED bit.

The clear_mask is first used to clear any bits indicated, and then the set_mask is used to set any bits indicated.


mx_object_signal() and mx_object_signal_peer() return MX_OK on success. In the event of failure, a negative error value is returned.


MX_ERR_BAD_HANDLE handle is not a valid handle.

MX_ERR_ACCESS_DENIED handle lacks the right MX_RIGHT_SIGNAL (for mx_object_signal()) or MX_RIGHT_SIGNAL_PEER (for mx_object_signal_peer()).

MX_ERR_INVALID_ARGS clear_mask or set_mask contain bits that are not allowed.

MX_ERR_NOT_SUPPORTED mx_object_signal_peer() used on an object lacking a peer.

MX_ERR_PEER_CLOSED mx_object_signal_peer() called on an object with a closed peer.


MX_RIGHT_WRITE is used to gate access to signal bits. This will likely change.


event_create, eventpair_create.