man3/pthread_cleanup_push_defer_np.3

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.TH PTHREAD_CLEANUP_PUSH_DEFER_NP 3 2021-03-22 "Linux" "Linux Programmer's Manual"
.SH NAME
pthread_cleanup_push_defer_np, pthread_cleanup_pop_restore_np \- push and pop
thread cancellation clean-up handlers while saving cancelability type
.SH SYNOPSIS
.nf
.B #include <pthread.h>
.PP
.BI "void pthread_cleanup_push_defer_np(void (*" routine ")(void *), void *" arg );
.BI "void pthread_cleanup_pop_restore_np(int " execute );
.fi
.PP
Compile and link with \fI\-pthread\fP.
.PP
.RS -4
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.RE
.PP
.BR pthread_cleanup_push_defer_np (),
.BR pthread_cleanup_pop_defer_np ():
.nf
    _GNU_SOURCE
.fi
.SH DESCRIPTION
These functions are the same as
.BR pthread_cleanup_push (3)
and
.BR pthread_cleanup_pop (3),
except for the differences noted on this page.
.PP
Like
.BR pthread_cleanup_push (3),
.BR pthread_cleanup_push_defer_np ()
pushes
.I routine
onto the thread's stack of cancellation clean-up handlers.
In addition, it also saves the thread's current cancelability type,
and sets the cancelability type to "deferred" (see
.BR pthread_setcanceltype (3));
this ensures that cancellation clean-up will occur
even if the thread's cancelability type was "asynchronous"
before the call.
.PP
Like
.BR pthread_cleanup_pop (3),
.BR pthread_cleanup_pop_restore_np ()
pops the top-most clean-up handler from the thread's
stack of cancellation clean-up handlers.
In addition, it restores the thread's cancelability
type to its value at the time of the matching
.BR pthread_cleanup_push_defer_np ().
.PP
The caller must ensure that calls to these
functions are paired within the same function,
and at the same lexical nesting level.
Other restrictions apply, as described in
.BR pthread_cleanup_push (3).
.PP
This sequence of calls:
.PP
.in +4n
.EX
pthread_cleanup_push_defer_np(routine, arg);
pthread_cleanup_pop_restore_np(execute);
.EE
.in
.PP
is equivalent to (but shorter and more efficient than):
.PP
.\" As far as I can see, LinuxThreads reverses the two substeps
.\" in the push and pop below.
.in +4n
.EX
int oldtype;

pthread_cleanup_push(routine, arg);
pthread_setcanceltype(PTHREAD_CANCEL_DEFERRED, &oldtype);
\&...
pthread_setcanceltype(oldtype, NULL);
pthread_cleanup_pop(execute);
.EE
.in
.\" SH VERSIONS
.\" Available since glibc 2.0
.SH CONFORMING TO
These functions are nonstandard GNU extensions;
hence the suffix "_np" (nonportable) in the names.
.SH SEE ALSO
.BR pthread_cancel (3),
.BR pthread_cleanup_push (3),
.BR pthread_setcancelstate (3),
.BR pthread_testcancel (3),
.BR pthreads (7)