#include <port.h> int port_alert(int port, int flags, int events, void *user);
The port_alert() function transitions a port into or out of alert mode. A port in alert mode immediately awakens all threads blocked in port_get(3C) or port_getn(3C). These threads return with an alert notification that consists of a single port_event_t structure with the source PORT_SOURCE_ALERT. Subsequent threads trying to retrieve events from a port that is in alert mode will return immediately with the alert notification.
A port is transitioned into alert mode by calling the port_alert() function with a non-zero events parameter. The specified events and user parameters will be made available in the portev_events and the portev_user members of the alert notification, respectively. The flags argument determines the mode of operation of the alert mode:
If flags is set to PORT_ALERT_SET, port_alert() sets the port in alert mode independent of the current state of the port. The portev_events and portev_user members are set or updated accordingly.
If flags is set to PORT_ALERT_UPDATE and the port is not in alert mode, port_alert() transitions the port into alert mode. The portev_events and portev_user members are set accordingly.
If flags is set to PORT_ALERT_UPDATE and the port is already in alert mode, port_alert() returns with an error value of EBUSY.
PORT_ALERT_SET and PORT_ALERT_UPDATE are mutually exclusive.
A port is transitioned out of alert mode by calling the port_alert() function with a zero events parameter.
Events can be queued to a port that is in alert mode, but they will not be retrievable until the port is transitioned out of alert mode.
Upon successful completion, 0 is returned. Otherwise, -1 is returned and errno is set to indicate the error.
The port_alert() function will fail if:
The port identifier is not valid.
The port argument is not an event port file descriptor.
The port is already in alert mode.
Mutually exclusive flags are set.
See attributes(5) for descriptions of the following attributes: