Technical Q&A QA1340

Registering and unregistering for sleep and wake notifications

Q: How can my application get notified when the computer is going to sleep or waking from sleep? How do I stop receiving these notifications?

A: Cocoa (Listing 1) and I/O Kit (Listing 3, Listing 4) can both be used to receive sleep and wake notifications. Cocoa can be used to receive sleep and wake notifications, while I/O Kit can also prevent or delay (Listing 2, Listing 3) idle sleep. However, even with I/O Kit, it is not possible to prevent forced sleep, only delay it.

Listing 1: Installing a Cocoa sleep and wake notification.

- (void) receiveSleepNote: (NSNotification*) note
{
    NSLog(@"receiveSleepNote: %@", [note name]);
}

- (void) receiveWakeNote: (NSNotification*) note
{
    NSLog(@"receiveSleepNote: %@", [note name]);
}

- (void) fileNotifications
{
    //These notifications are filed on NSWorkspace's notification center, not the default notification center. 
    //  You will not receive sleep/wake notifications if you file with the default notification center.
    [[[NSWorkspace sharedWorkspace] notificationCenter] addObserver: self 
            selector: @selector(receiveSleepNote:) name: NSWorkspaceWillSleepNotification object: NULL];
    [[[NSWorkspace sharedWorkspace] notificationCenter] addObserver: self 
            selector: @selector(receiveWakeNote:) name: NSWorkspaceDidWakeNotification object: NULL];
}

Listing 2: Preventing sleep using I/O Kit in Mac OS X 10.5 Leopard

...

#import <IOKit/pwr_mgt/IOPMLib.h>

...
// kIOPMAssertionTypeNoDisplaySleep prevents display sleep,
// kIOPMAssertionTypeNoIdleSleep prevents idle sleep

IOPMAssertionID assertionID;
IOReturn success = IOPMAssertionCreate(kIOPMAssertionTypeNoDisplaySleep, 
                                    kIOPMAssertionLevelOn, &assertionID); 
if (success == kIOReturnSuccess)
{

    //Add the work you need to do without 
    //  the system sleeping here.

    success = IOPMAssertionRelease(assertionID);
    //The system will be able to sleep again. 
}
...

Listing 3: Installing an I/O Kit sleep/wake notification.

#include <ctype.h>
#include <stdlib.h>
#include <stdio.h>

#include <mach/mach_port.h>
#include <mach/mach_interface.h>
#include <mach/mach_init.h>

#include <IOKit/pwr_mgt/IOPMLib.h>
#include <IOKit/IOMessage.h>

io_connect_t  root_port; // a reference to the Root Power Domain IOService

void
MySleepCallBack( void * refCon, io_service_t service, natural_t messageType, void * messageArgument )
{
    printf( "messageType %08lx, arg %08lx\n",
        (long unsigned int)messageType,
        (long unsigned int)messageArgument );

    switch ( messageType )
    {

        case kIOMessageCanSystemSleep:
            /* Idle sleep is about to kick in. This message will not be sent for forced sleep.
                Applications have a chance to prevent sleep by calling IOCancelPowerChange.
                Most applications should not prevent idle sleep.

                Power Management waits up to 30 seconds for you to either allow or deny idle sleep.
                If you don't acknowledge this power change by calling either IOAllowPowerChange
                or IOCancelPowerChange, the system will wait 30 seconds then go to sleep.
            */

            //Uncomment to cancel idle sleep
            //IOCancelPowerChange( root_port, (long)messageArgument );
            // we will allow idle sleep
            IOAllowPowerChange( root_port, (long)messageArgument );
            break;

        case kIOMessageSystemWillSleep:
            /* The system WILL go to sleep. If you do not call IOAllowPowerChange or
                IOCancelPowerChange to acknowledge this message, sleep will be
                delayed by 30 seconds.

                NOTE: If you call IOCancelPowerChange to deny sleep it returns kIOReturnSuccess,
                however the system WILL still go to sleep. 
            */

            IOAllowPowerChange( root_port, (long)messageArgument );
            break;

        case kIOMessageSystemWillPowerOn:
            //System has started the wake up process...
            break;

        case kIOMessageSystemHasPoweredOn:
            //System has finished waking up...
        break;

        default:
            break;

    }
}


int main( int argc, char **argv )
{
    IONotificationPortRef  notifyPortRef; // notification port allocated by IORegisterForSystemPower
    io_object_t            notifierObject; // notifier object, used to deregister later
    void*                  refCon; // this parameter is passed to the callback

    // register to receive system sleep notifications

    root_port = IORegisterForSystemPower( refCon, &notifyPortRef, MySleepCallBack, &notifierObject );
    if ( root_port == 0 )
    {
        printf("IORegisterForSystemPower failed\n");
        return 1;
    }

    // add the notification port to the application runloop
    CFRunLoopAddSource( CFRunLoopGetCurrent(),
            IONotificationPortGetRunLoopSource(notifyPortRef), kCFRunLoopCommonModes ); 

    /* Start the run loop to receive sleep notifications. Don't call CFRunLoopRun if this code 
        is running on the main thread of a Cocoa or Carbon application. Cocoa and Carbon manage 
        the main thread's run loop for you as part of their event handling mechanisms. */ 
    CFRunLoopRun();

    //Not reached, CFRunLoopRun doesn't return in this case.
    return (0);
}

To stop receiving I/O Kit sleep notifications, you need to remove your event source from the application runloop and do a bit of cleanup.

Listing 4: Removing I/O Kit sleep/wake notification handler.

...
    // we no longer want sleep notifications:

    // remove the sleep notification port from the application runloop
    CFRunLoopRemoveSource( CFRunLoopGetCurrent(),
                           IONotificationPortGetRunLoopSource(notifyPortRef),
                           kCFRunLoopCommonModes );

    // deregister for system sleep notifications
    IODeregisterForSystemPower( &notifierObject );

    // IORegisterForSystemPower implicitly opens the Root Power Domain IOService
    // so we close it here
    IOServiceClose( root_port );

    // destroy the notification port allocated by IORegisterForSystemPower
    IONotificationPortDestroy( notifyPortRef );
...

Document Revision History

Posted: 2008-08-08