pthread_setcancelstate(3) manual page

The pthread_setcancelstate() and pthread_setcanceltype() functions are used to control the points at which a thread may be asynchronously canceled. For cancellation control to be usable in modular fashion, some rules must be followed.

For purposes of this discussion, consider an object to be a generalization of a procedure. It is a set of procedures and global variables written as a unit and called by clients not known by the object. Objects may depend on other objects.

First, cancelability should only be disabled on entry to an object, never explicitly enabled. On exit from an object, the cancelability state should always be restored to its value on entry to the object.

This follows from a modularity argument: if the client of an object (or the client of an object that uses that object) has disabled cancelability, it is because the client does not want to have to worry about how to clean up if the thread is canceled while executing some sequence of actions. If an object is called in such a state and it enables cancelability and a cancellation request is pending for that thread, then the thread will be canceled, contrary to the wish of the client that disabled.

Second, the cancelability type may be explicitly set to either deferred or asynchronous upon entry to an object. But as with the cancelability state, on exit from an object that cancelability type should always be restored to its value on entry to the object.

Finally, only functions that are cancel-safe may be called from a thread that is asynchronously cancelable.

`accept()` `accept4()` `aio_suspend()` `connect()` `clock_nanosleep()` `close()` `creat()` `fcntl()`
	The `fcntl()` function is a cancellation point if cmd is `F_SETLKW`.
`fdatasync()` `fsync()` `kevent()`
	The `kevent()` function is a cancellation point if it is potentially blocking, such as when the nevents argument is non-zero.
`mq_receive()` `mq_send()` `mq_timedreceive()` `mq_timedsend()` `msync()` `nanosleep()` `open()` `openat()` `pause()` `poll()` `ppoll()` `pselect()` `pthread_cond_timedwait()` `pthread_cond_wait()` `pthread_join()` `pthread_testcancel()` `read()` `readv()` `recv()` `recvfrom()` `recvmsg()` `select()` `sem_timedwait()` `sem_clockwait_np()` `sem_wait()` `send()` `sendmsg()` `sendto()` `sigsuspend()` `sigtimedwait()` `sigwaitinfo()` `sigwait()` `sleep()` `system()` `tcdrain()` `usleep()` `wait()` `wait3()` `wait4()` `wait6()` `waitid()` `waitpid()` `write()` `writev()`

“	Do you laugh when the waiter drops a tray full of dishes? Unix weenies do. They're the first ones to laugh at hapless users, trying to figure out an error message that doesn't have anything to do with what they just typed.	”
— The Unix Haters' handbook

Manual Pages — PTHREAD_TESTCANCEL

NAME

CONTENTS

LIBRARY

SYNOPSIS

DESCRIPTION

Cancelability States

Cancellation Points

NOTES

RETURN VALUES

ERRORS

SEE ALSO

STANDARDS

AUTHORS

[`EINVAL`]
	The specified state is not `PTHREAD_CANCEL_ENABLE` or `PTHREAD_CANCEL_DISABLE`.