CFFileDescriptor

The CFFileDescriptor provides an opaque type to monitor file descriptors for read and write activity via CFRunLoop.

Overview

You use CFFileDescriptor to monitor file descriptors for read and write activity via CFRunLoop using callbacks. Each call back is one-shot, and must be re-enabled if you want to get another one.

You can re-enable the callback in the callback function itself, but you must completely service the file descriptor before doing so. For example, if you create a CFFileDescriptor for a pipe and get a callback because there are bytes to be read, then if you don't read all of the bytes but nevertheless re-enable the CFFileDescriptor for read activity, you'll get called back again immediately.

You can monitor kqueue file descriptors for read activity to find out when an event the kqueue is filtering for has occurred. You are responsible for understanding the use of the kevent() API and inserting and removing filters from the kqueue file descriptor yourself.

The following example takes a UNIX process ID as argument, and watches up to 20 seconds, and reports if the process terminates in that time:

// cc test.c -framework CoreFoundation -O
#include <CoreFoundation/CoreFoundation.h>
#include <unistd.h>
#include <sys/event.h>
static void noteProcDeath(CFFileDescriptorRef fdref, CFOptionFlags callBackTypes, void *info) {
    struct kevent kev;
    int fd = CFFileDescriptorGetNativeDescriptor(fdref);
    kevent(fd, NULL, 0, &kev, 1, NULL);
    // take action on death of process here
    printf("process with pid '%u' died\n", (unsigned int)kev.ident);
    CFFileDescriptorInvalidate(fdref);
    CFRelease(fdref); // the CFFileDescriptorRef is no longer of any use in this example
}
// one argument, an integer pid to watch, required
int main(int argc, char *argv[]) {
    if (argc < 2) exit(1);
    int fd = kqueue();
    struct kevent kev;
    EV_SET(&kev, atoi(argv[1]), EVFILT_PROC, EV_ADD|EV_ENABLE, NOTE_EXIT, 0, NULL);
    kevent(fd, &kev, 1, NULL, 0, NULL);
    CFFileDescriptorRef fdref = CFFileDescriptorCreate(kCFAllocatorDefault, fd, true, noteProcDeath, NULL);
    CFFileDescriptorEnableCallBacks(fdref, kCFFileDescriptorReadCallBack);
    CFRunLoopSourceRef source = CFFileDescriptorCreateRunLoopSource(kCFAllocatorDefault, fdref, 0);
    CFRunLoopAddSource(CFRunLoopGetMain(), source, kCFRunLoopDefaultMode);
    CFRelease(source);
    // run the run loop for 20 seconds
    CFRunLoopRunInMode(kCFRunLoopDefaultMode, 20.0, false);
    return 0;
}

Symbols

Getting Information About a File Descriptor

func CFFileDescriptorGetNativeDescriptor(CFFileDescriptor!)

Returns the native file descriptor for a given CFFileDescriptor.

func CFFileDescriptorIsValid(CFFileDescriptor!)

Returns a Boolean value that indicates whether the native file descriptor for a given CFFileDescriptor is valid.

Invalidating a File Descriptor

func CFFileDescriptorInvalidate(CFFileDescriptor!)

Invalidates a CFFileDescriptor object.

Managing Callbacks

func CFFileDescriptorEnableCallBacks(CFFileDescriptor!, CFOptionFlags)

Enables callbacks for a given CFFileDescriptor.

func CFFileDescriptorDisableCallBacks(CFFileDescriptor!, CFOptionFlags)

Disables callbacks for a given CFFileDescriptor.

Creating a Run Loop Source

func CFFileDescriptorCreateRunLoopSource(CFAllocator!, CFFileDescriptor!, CFIndex)

Creates a new runloop source for a given CFFileDescriptor.

Getting the CFFileDescriptor Type ID

func CFFileDescriptorGetTypeID()

Returns the type identifier for the CFFileDescriptor opaque type.

Data Types

CFFileDescriptorNativeDescriptor

Defines a type for the native file descriptor.

CFFileDescriptorCallBack

Defines a structure for a callback for a CFFileDescriptor.

CFFileDescriptorContext

Defines a structure for the context of a CFFileDescriptor.

CFFileDescriptor

A reference to an CFFileDescriptor object.

Constants

Callback Identifiers

Constants that identify the read and write callbacks.