And one more for today... Any reviewers for pthread_setcancelstate(3)? Cheers, Michael .\" Copyright (c) 2008 Linux Foundation, written by Michael Kerrisk .\" <mtk.manpages@xxxxxxxxx> .\" .\" Permission is granted to make and distribute verbatim copies of this .\" manual provided the copyright notice and this permission notice are .\" preserved on all copies. .\" .\" Permission is granted to copy and distribute modified versions of this .\" manual under the conditions for verbatim copying, provided that the .\" entire resulting derived work is distributed under the terms of a .\" permission notice identical to this one. .\" .\" Since the Linux kernel and libraries are constantly changing, this .\" manual page may be incorrect or out-of-date. The author(s) assume no .\" responsibility for errors or omissions, or for damages resulting from .\" the use of the information contained herein. The author(s) may not .\" have taken the same level of care in the production of this manual, .\" which is licensed free of charge, as they might when working .\" professionally. .\" .\" Formatted or processed versions of this manual, if unaccompanied by .\" the source, must acknowledge the copyright and authors of this work. .\" .TH PTHREAD_SETCANCELSTATE 3 2008-11-14 "Linux" "Linux Programmer's Manual" .SH NAME pthread_setcancelstate, pthread_setcanceltype \- set cancelability state and type .SH SYNOPSIS .nf .B #include <pthread.h> .BI "int pthread_setcancelstate(int " state ", int *" oldstate ); .BI "int pthread_setcanceltype(int " type ", int *" oldtype ); .sp Compile and link with \fI\-pthread\fP. .SH DESCRIPTION The .BR pthread_setcancelstate () sets the cancelability state of the calling thread to the value given in .IR state . The previous cancelability state of the thread is returned in the buffer pointed to by .IR oldstate . The .I state argument must have one of the following values: .TP .B PTHREAD_CANCEL_ENABLE The thread is cancelable. This is the default cancelability state in all new threads, including the initial thread. The thread's cancelability type determines when a cancelable thread will respond to a cancellation request. .TP .B PTHREAD_CANCEL_DISABLE The thread is not cancelable. If a cancellation request is received, it is blocked until cancelability is enabled. .PP The .BR pthread_setcanceltype () sets the cancelability type of the calling thread to the value given in .IR type . The previous cancelability type of the thread is returned in the buffer pointed to by .IR oldtype . The .I type argument must have one of the following values: .TP .B PTHREAD_CANCEL_DEFERRED A cancellation request is deferred until the thread next calls a function that is a cancellation point (see .BR pthreads (7)). This is the default cancelability type in all new threads, including the initial thread. .TP .B PTHREAD_CANCEL_ASYNCHRONOUS The thread can be canceled at any time. (Typically, it will be canceled immediately upon receiving a cancellation request, but the system doesn't guarantee this.) .PP The set-and-get operation performed by each of these functions is atomic with respect to other threads in the process calling the same function. .SH RETURN VALUE On success, these functions return 0; on error, they return a non-zero error number. .SH ERRORS The .BR pthread_setcancelstate () can fail with the following error: .TP .B EINVAL Invalid value for .IR state . .PP The .BR pthread_setcanceltype () can fail with the following error: .TP .B EINVAL Invalid value for .IR type . .\" .SH VERSIONS .\" Available since glibc 2.0 .SH CONFORMING TO POSIX.1-2001. .SH NOTES For details of what happens when a thread is canceled, see .BR pthread_cancel (3). Briefly disabling cancelability is useful if a thread performs some critical action that must not be interrupted by a cancellation request. Beware of disabling cancelability for long periods, or around operations that may block for long periods, since that will render the thread unresponsive to cancellation requests. Setting the cancelability type to .B PTHREAD_CANCEL_ASYNCHRONOUS is rarely useful. Since the thread could be canceled at .I any time, it cannot reserve resources (e.g., allocating memory), acquire mutexes, semaphores, or locks, and so on, since, when the thread is canceled, the application has no way of knowing what the state of these resources is; that is, did the canceled thread manage to release the resources or not? (Among other things, this means that clean-up handlers cease to be useful, since they can't determine the state of resources that they are intended to clean up.) In general, most library functions, including most pthreads functions, can't be safely called from an asynchronously cancelable thread. (POSIX.1-2001 only requires that .BR pthread_cancel (3), .BR pthread_setcancelstate (), and .BR pthread_setcanceltype () be safe to call from an asynchronously cancelable thread.) One of the few circumstances in which asynchronous cancelability is useful is for cancellation of a thread that is in a pure compute-bound loop. The Linux threading implementations permit the .I oldstate argument of .BR pthread_setcancelstate () to be NULL, in which case the information about the previous cancelability state is not returned to the caller. Many other implementations also permit a NULL .I oldstat argument, .\" It looks like at least Solaris, FreeBSD and Tru64 support this. but POSIX.1-2001 does not specify this point, so portable applications should always specify a non-NULL value in .IR oldstate . A precisely analogous set of statements applies for the .I oldtype argument of .BR pthread_setcanceltype (). .SH EXAMPLE See .BR pthread_cancel (3). .SH SEE ALSO .BR pthread_cleanup_push (3), .BR pthread_cancel (3), .BR pthread_testcancel (3), .BR pthreads (7) -- To unsubscribe from this list: send the line "unsubscribe linux-man" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
