Provide asynchronous event notification
int PhEventRead( int rcvid, void *buffer, unsigned size );
ph
This function provides an asynchronous event-notification mechanism. You'll find it useful for applications that need to interact with Photon but also need to collect Neutrino pulses or messages from other processes.
For synchronous event notification, see PhEventNext() and PhEventPeek().
The widget library calls PhEventRead() internally; if you call PhEventRead() in an application that uses widgets, you might get unexpected results. Use PtMainLoop() or PtProcessEvent() instead. |
Typically, you call this function with the rcvid returned by MsgReceive() to see if the message received was a pulse sent by Photon.
If the message received is the application's event pulse, then:
If the message isn't the application's event pulse, PhEventRead() returns 0.
Photon may close a region (for example, via the window manager) before you read the pending event. As a result, PhEventRead() may indicate that no event is pending even though you were notified otherwise. In this case, PhEventRead() returns -1 and sets errno to ENOMSG.
You must call PhAttach() and arm the event pulse by calling PhEventArm() before you call PhEventRead() for the first time. |
This code fragment shows how you can use PhEventRead() with PhGetMsgSize() to maintain a dynamic event buffer. You need to define my_msg_struct, initialize(), and process_app_msg():
#include <stdlib.h> #include <errno.h> #include <sys/neutrino.h> #include <Pt.h> int initialize( void ); void process_app_msg( void * ); int main( int argc, char *argv[] ) { int rcvid, chid; void *msg; unsigned msg_size; if( initialize() == -1 ) exit( EXIT_FAILURE ); msg_size = sizeof (my_msg_struct); if ( !(msg = malloc( msg_size ))) { errno = ENOMEM; return( EXIT_FAILURE ); } PhEventArm(); chid = PhChannelAttach( 0, -1, NULL ); while( 1 ) { rcvid = MsgReceive( chid, msg, msg_size, NULL ); switch( PhEventRead( rcvid, msg, msg_size)) { case Ph_EVENT_MSG: PtEventHandler( (PhEvent_t *)msg ); break; case Ph_RESIZE_MSG: msg_size = PhGetMsgSize( (PhEvent_t *)msg ); if( !( msg = realloc( msg, msg_size ))) { errno = ENOMEM; return( EXIT_FAILURE ); } break; case 0: process_app_msg( msg ); break; case -1: perror( "PhEventRead failed" ); break; } } return( EXIT_SUCCESS ); }
Photon
Safety: | |
---|---|
Interrupt handler | No |
Signal handler | No |
Thread | No |
PhAttach(), PhEvent_t, PhEventArm(), PhEventNext(), PhEventPeek(), PhGetMsgSize(), PtEventHandler()
“Collecting events” in the Events chapter of the Photon Programmer's Guide
MsgReceive() in the QNX Neutrino Library Reference