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diff --git a/man7/pthreads.7 b/man7/pthreads.7 new file mode 100644 index 0000000..2c00798 --- /dev/null +++ b/man7/pthreads.7 @@ -0,0 +1,937 @@ +.\" Copyright (c) 2005 by Michael Kerrisk <mtk.manpages@gmail.com> +.\" +.\" SPDX-License-Identifier: Linux-man-pages-copyleft +.\" +.TH pthreads 7 2023-03-18 "Linux man-pages 6.05.01" +.SH NAME +pthreads \- POSIX threads +.SH DESCRIPTION +POSIX.1 specifies a set of interfaces (functions, header files) for +threaded programming commonly known as POSIX threads, or Pthreads. +A single process can contain multiple threads, +all of which are executing the same program. +These threads share the same global memory (data and heap segments), +but each thread has its own stack (automatic variables). +.PP +POSIX.1 also requires that threads share a range of other attributes +(i.e., these attributes are process-wide rather than per-thread): +.IP \[bu] 3 +process ID +.IP \[bu] +parent process ID +.IP \[bu] +process group ID and session ID +.IP \[bu] +controlling terminal +.IP \[bu] +user and group IDs +.IP \[bu] +open file descriptors +.IP \[bu] +record locks (see +.BR fcntl (2)) +.IP \[bu] +signal dispositions +.IP \[bu] +file mode creation mask +.RB ( umask (2)) +.IP \[bu] +current directory +.RB ( chdir (2)) +and +root directory +.RB ( chroot (2)) +.IP \[bu] +interval timers +.RB ( setitimer (2)) +and POSIX timers +.RB ( timer_create (2)) +.IP \[bu] +nice value +.RB ( setpriority (2)) +.IP \[bu] +resource limits +.RB ( setrlimit (2)) +.IP \[bu] +measurements of the consumption of CPU time +.RB ( times (2)) +and resources +.RB ( getrusage (2)) +.PP +As well as the stack, POSIX.1 specifies that various other +attributes are distinct for each thread, including: +.IP \[bu] 3 +thread ID (the +.I pthread_t +data type) +.IP \[bu] +signal mask +.RB ( pthread_sigmask (3)) +.IP \[bu] +the +.I errno +variable +.IP \[bu] +alternate signal stack +.RB ( sigaltstack (2)) +.IP \[bu] +real-time scheduling policy and priority +.RB ( sched (7)) +.PP +The following Linux-specific features are also per-thread: +.IP \[bu] 3 +capabilities (see +.BR capabilities (7)) +.IP \[bu] +CPU affinity +.RB ( sched_setaffinity (2)) +.SS Pthreads function return values +Most pthreads functions return 0 on success, and an error number on failure. +The error numbers that can be returned have the same meaning as +the error numbers returned in +.I errno +by conventional system calls and C library functions. +Note that the pthreads functions do not set +.IR errno . +For each of the pthreads functions that can return an error, +POSIX.1-2001 specifies that the function can never fail with the error +.BR EINTR . +.SS Thread IDs +Each of the threads in a process has a unique thread identifier +(stored in the type +.IR pthread_t ). +This identifier is returned to the caller of +.BR pthread_create (3), +and a thread can obtain its own thread identifier using +.BR pthread_self (3). +.PP +Thread IDs are guaranteed to be unique only within a process. +(In all pthreads functions that accept a thread ID as an argument, +that ID by definition refers to a thread in +the same process as the caller.) +.PP +The system may reuse a thread ID after a terminated thread has been joined, +or a detached thread has terminated. +POSIX says: "If an application attempts to use a thread ID whose +lifetime has ended, the behavior is undefined." +.SS Thread-safe functions +A thread-safe function is one that can be safely +(i.e., it will deliver the same results regardless of whether it is) +called from multiple threads at the same time. +.PP +POSIX.1-2001 and POSIX.1-2008 require that all functions specified +in the standard shall be thread-safe, +except for the following functions: +.PP +.in +4n +.EX +asctime() +basename() +catgets() +crypt() +ctermid() if passed a non-NULL argument +ctime() +dbm_clearerr() +dbm_close() +dbm_delete() +dbm_error() +dbm_fetch() +dbm_firstkey() +dbm_nextkey() +dbm_open() +dbm_store() +dirname() +dlerror() +drand48() +ecvt() [POSIX.1-2001 only (function removed in POSIX.1-2008)] +encrypt() +endgrent() +endpwent() +endutxent() +fcvt() [POSIX.1-2001 only (function removed in POSIX.1-2008)] +ftw() +gcvt() [POSIX.1-2001 only (function removed in POSIX.1-2008)] +getc_unlocked() +getchar_unlocked() +getdate() +getenv() +getgrent() +getgrgid() +getgrnam() +gethostbyaddr() [POSIX.1-2001 only (function removed in + POSIX.1-2008)] +gethostbyname() [POSIX.1-2001 only (function removed in + POSIX.1-2008)] +gethostent() +getlogin() +getnetbyaddr() +getnetbyname() +getnetent() +getopt() +getprotobyname() +getprotobynumber() +getprotoent() +getpwent() +getpwnam() +getpwuid() +getservbyname() +getservbyport() +getservent() +getutxent() +getutxid() +getutxline() +gmtime() +hcreate() +hdestroy() +hsearch() +inet_ntoa() +l64a() +lgamma() +lgammaf() +lgammal() +localeconv() +localtime() +lrand48() +mrand48() +nftw() +nl_langinfo() +ptsname() +putc_unlocked() +putchar_unlocked() +putenv() +pututxline() +rand() +readdir() +setenv() +setgrent() +setkey() +setpwent() +setutxent() +strerror() +strsignal() [Added in POSIX.1-2008] +strtok() +system() [Added in POSIX.1-2008] +tmpnam() if passed a non-NULL argument +ttyname() +unsetenv() +wcrtomb() if its final argument is NULL +wcsrtombs() if its final argument is NULL +wcstombs() +wctomb() +.EE +.in +.SS Async-cancel-safe functions +An async-cancel-safe function is one that can be safely called +in an application where asynchronous cancelability is enabled (see +.BR pthread_setcancelstate (3)). +.PP +Only the following functions are required to be async-cancel-safe by +POSIX.1-2001 and POSIX.1-2008: +.PP +.in +4n +.EX +pthread_cancel() +pthread_setcancelstate() +pthread_setcanceltype() +.EE +.in +.SS Cancelation points +POSIX.1 specifies that certain functions must, +and certain other functions may, be cancelation points. +If a thread is cancelable, its cancelability type is deferred, +and a cancelation request is pending for the thread, +then the thread is canceled when it calls a function +that is a cancelation point. +.PP +The following functions are required to be cancelation points by +POSIX.1-2001 and/or POSIX.1-2008: +.PP +.\" FIXME +.\" Document the list of all functions that are cancelation points in glibc +.in +4n +.EX +accept() +aio_suspend() +clock_nanosleep() +close() +connect() +creat() +fcntl() F_SETLKW +fdatasync() +fsync() +getmsg() +getpmsg() +lockf() F_LOCK +mq_receive() +mq_send() +mq_timedreceive() +mq_timedsend() +msgrcv() +msgsnd() +msync() +nanosleep() +open() +openat() [Added in POSIX.1-2008] +pause() +poll() +pread() +pselect() +pthread_cond_timedwait() +pthread_cond_wait() +pthread_join() +pthread_testcancel() +putmsg() +putpmsg() +pwrite() +read() +readv() +recv() +recvfrom() +recvmsg() +select() +sem_timedwait() +sem_wait() +send() +sendmsg() +sendto() +sigpause() [POSIX.1-2001 only (moves to "may" list in POSIX.1-2008)] +sigsuspend() +sigtimedwait() +sigwait() +sigwaitinfo() +sleep() +system() +tcdrain() +usleep() [POSIX.1-2001 only (function removed in POSIX.1-2008)] +wait() +waitid() +waitpid() +write() +writev() +.EE +.in +.PP +The following functions may be cancelation points according to +POSIX.1-2001 and/or POSIX.1-2008: +.PP +.in +4n +.EX +access() +asctime() +asctime_r() +catclose() +catgets() +catopen() +chmod() [Added in POSIX.1-2008] +chown() [Added in POSIX.1-2008] +closedir() +closelog() +ctermid() +ctime() +ctime_r() +dbm_close() +dbm_delete() +dbm_fetch() +dbm_nextkey() +dbm_open() +dbm_store() +dlclose() +dlopen() +dprintf() [Added in POSIX.1-2008] +endgrent() +endhostent() +endnetent() +endprotoent() +endpwent() +endservent() +endutxent() +faccessat() [Added in POSIX.1-2008] +fchmod() [Added in POSIX.1-2008] +fchmodat() [Added in POSIX.1-2008] +fchown() [Added in POSIX.1-2008] +fchownat() [Added in POSIX.1-2008] +fclose() +fcntl() (for any value of cmd argument) +fflush() +fgetc() +fgetpos() +fgets() +fgetwc() +fgetws() +fmtmsg() +fopen() +fpathconf() +fprintf() +fputc() +fputs() +fputwc() +fputws() +fread() +freopen() +fscanf() +fseek() +fseeko() +fsetpos() +fstat() +fstatat() [Added in POSIX.1-2008] +ftell() +ftello() +ftw() +futimens() [Added in POSIX.1-2008] +fwprintf() +fwrite() +fwscanf() +getaddrinfo() +getc() +getc_unlocked() +getchar() +getchar_unlocked() +getcwd() +getdate() +getdelim() [Added in POSIX.1-2008] +getgrent() +getgrgid() +getgrgid_r() +getgrnam() +getgrnam_r() +gethostbyaddr() [POSIX.1-2001 only (function removed in + POSIX.1-2008)] +gethostbyname() [POSIX.1-2001 only (function removed in + POSIX.1-2008)] +gethostent() +gethostid() +gethostname() +getline() [Added in POSIX.1-2008] +getlogin() +getlogin_r() +getnameinfo() +getnetbyaddr() +getnetbyname() +getnetent() +getopt() (if opterr is nonzero) +getprotobyname() +getprotobynumber() +getprotoent() +getpwent() +getpwnam() +getpwnam_r() +getpwuid() +getpwuid_r() +gets() +getservbyname() +getservbyport() +getservent() +getutxent() +getutxid() +getutxline() +getwc() +getwchar() +getwd() [POSIX.1-2001 only (function removed in POSIX.1-2008)] +glob() +iconv_close() +iconv_open() +ioctl() +link() +linkat() [Added in POSIX.1-2008] +lio_listio() [Added in POSIX.1-2008] +localtime() +localtime_r() +lockf() [Added in POSIX.1-2008] +lseek() +lstat() +mkdir() [Added in POSIX.1-2008] +mkdirat() [Added in POSIX.1-2008] +mkdtemp() [Added in POSIX.1-2008] +mkfifo() [Added in POSIX.1-2008] +mkfifoat() [Added in POSIX.1-2008] +mknod() [Added in POSIX.1-2008] +mknodat() [Added in POSIX.1-2008] +mkstemp() +mktime() +nftw() +opendir() +openlog() +pathconf() +pclose() +perror() +popen() +posix_fadvise() +posix_fallocate() +posix_madvise() +posix_openpt() +posix_spawn() +posix_spawnp() +posix_trace_clear() +posix_trace_close() +posix_trace_create() +posix_trace_create_withlog() +posix_trace_eventtypelist_getnext_id() +posix_trace_eventtypelist_rewind() +posix_trace_flush() +posix_trace_get_attr() +posix_trace_get_filter() +posix_trace_get_status() +posix_trace_getnext_event() +posix_trace_open() +posix_trace_rewind() +posix_trace_set_filter() +posix_trace_shutdown() +posix_trace_timedgetnext_event() +posix_typed_mem_open() +printf() +psiginfo() [Added in POSIX.1-2008] +psignal() [Added in POSIX.1-2008] +pthread_rwlock_rdlock() +pthread_rwlock_timedrdlock() +pthread_rwlock_timedwrlock() +pthread_rwlock_wrlock() +putc() +putc_unlocked() +putchar() +putchar_unlocked() +puts() +pututxline() +putwc() +putwchar() +readdir() +readdir_r() +readlink() [Added in POSIX.1-2008] +readlinkat() [Added in POSIX.1-2008] +remove() +rename() +renameat() [Added in POSIX.1-2008] +rewind() +rewinddir() +scandir() [Added in POSIX.1-2008] +scanf() +seekdir() +semop() +setgrent() +sethostent() +setnetent() +setprotoent() +setpwent() +setservent() +setutxent() +sigpause() [Added in POSIX.1-2008] +stat() +strerror() +strerror_r() +strftime() +symlink() +symlinkat() [Added in POSIX.1-2008] +sync() +syslog() +tmpfile() +tmpnam() +ttyname() +ttyname_r() +tzset() +ungetc() +ungetwc() +unlink() +unlinkat() [Added in POSIX.1-2008] +utime() [Added in POSIX.1-2008] +utimensat() [Added in POSIX.1-2008] +utimes() [Added in POSIX.1-2008] +vdprintf() [Added in POSIX.1-2008] +vfprintf() +vfwprintf() +vprintf() +vwprintf() +wcsftime() +wordexp() +wprintf() +wscanf() +.EE +.in +.PP +An implementation may also mark other functions +not specified in the standard as cancelation points. +In particular, an implementation is likely to mark +any nonstandard function that may block as a cancelation point. +(This includes most functions that can touch files.) +.PP +It should be noted that even if an application is not using +asynchronous cancelation, that calling a function from the above list +from an asynchronous signal handler may cause the equivalent of +asynchronous cancelation. +The underlying user code may not expect +asynchronous cancelation and the state of the user data may become +inconsistent. +Therefore signals should be used with caution when +entering a region of deferred cancelation. +.\" So, scanning "cancelation point" comments in the glibc 2.8 header +.\" files, it looks as though at least the following nonstandard +.\" functions are cancelation points: +.\" endnetgrent +.\" endspent +.\" epoll_pwait +.\" epoll_wait +.\" fcloseall +.\" fdopendir +.\" fflush_unlocked +.\" fgetc_unlocked +.\" fgetgrent +.\" fgetgrent_r +.\" fgetpwent +.\" fgetpwent_r +.\" fgets_unlocked +.\" fgetspent +.\" fgetspent_r +.\" fgetwc_unlocked +.\" fgetws_unlocked +.\" fputc_unlocked +.\" fputs_unlocked +.\" fputwc_unlocked +.\" fputws_unlocked +.\" fread_unlocked +.\" fwrite_unlocked +.\" gai_suspend +.\" getaddrinfo_a +.\" getdate_r +.\" getgrent_r +.\" getgrouplist +.\" gethostbyaddr_r +.\" gethostbyname2 +.\" gethostbyname2_r +.\" gethostbyname_r +.\" gethostent_r +.\" getnetbyaddr_r +.\" getnetbyname_r +.\" getnetent_r +.\" getnetgrent +.\" getnetgrent_r +.\" getprotobyname_r +.\" getprotobynumber_r +.\" getprotoent_r +.\" getpw +.\" getpwent_r +.\" getservbyname_r +.\" getservbyport_r +.\" getservent_r +.\" getspent +.\" getspent_r +.\" getspnam +.\" getspnam_r +.\" getutmp +.\" getutmpx +.\" getw +.\" getwc_unlocked +.\" getwchar_unlocked +.\" initgroups +.\" innetgr +.\" mkostemp +.\" mkostemp64 +.\" mkstemp64 +.\" ppoll +.\" pthread_timedjoin_np +.\" putgrent +.\" putpwent +.\" putspent +.\" putw +.\" putwc_unlocked +.\" putwchar_unlocked +.\" rcmd +.\" rcmd_af +.\" rexec +.\" rexec_af +.\" rresvport +.\" rresvport_af +.\" ruserok +.\" ruserok_af +.\" setnetgrent +.\" setspent +.\" sgetspent +.\" sgetspent_r +.\" updwtmpx +.\" utmpxname +.\" vfscanf +.\" vfwscanf +.\" vscanf +.\" vsyslog +.\" vwscanf +.SS Compiling on Linux +On Linux, programs that use the Pthreads API should be compiled using +.IR "cc \-pthread" . +.SS Linux implementations of POSIX threads +Over time, two threading implementations have been provided by +the GNU C library on Linux: +.TP +.B LinuxThreads +This is the original Pthreads implementation. +Since glibc 2.4, this implementation is no longer supported. +.TP +.BR NPTL " (Native POSIX Threads Library)" +This is the modern Pthreads implementation. +By comparison with LinuxThreads, NPTL provides closer conformance to +the requirements of the POSIX.1 specification and better performance +when creating large numbers of threads. +NPTL is available since glibc 2.3.2, +and requires features that are present in the Linux 2.6 kernel. +.PP +Both of these are so-called 1:1 implementations, meaning that each +thread maps to a kernel scheduling entity. +Both threading implementations employ the Linux +.BR clone (2) +system call. +In NPTL, thread synchronization primitives (mutexes, +thread joining, and so on) are implemented using the Linux +.BR futex (2) +system call. +.SS LinuxThreads +The notable features of this implementation are the following: +.IP \[bu] 3 +In addition to the main (initial) thread, +and the threads that the program creates using +.BR pthread_create (3), +the implementation creates a "manager" thread. +This thread handles thread creation and termination. +(Problems can result if this thread is inadvertently killed.) +.IP \[bu] +Signals are used internally by the implementation. +On Linux 2.2 and later, the first three real-time signals are used +(see also +.BR signal (7)). +On older Linux kernels, +.B SIGUSR1 +and +.B SIGUSR2 +are used. +Applications must avoid the use of whichever set of signals is +employed by the implementation. +.IP \[bu] +Threads do not share process IDs. +(In effect, LinuxThreads threads are implemented as processes which share +more information than usual, but which do not share a common process ID.) +LinuxThreads threads (including the manager thread) +are visible as separate processes using +.BR ps (1). +.PP +The LinuxThreads implementation deviates from the POSIX.1 +specification in a number of ways, including the following: +.IP \[bu] 3 +Calls to +.BR getpid (2) +return a different value in each thread. +.IP \[bu] +Calls to +.BR getppid (2) +in threads other than the main thread return the process ID of the +manager thread; instead +.BR getppid (2) +in these threads should return the same value as +.BR getppid (2) +in the main thread. +.IP \[bu] +When one thread creates a new child process using +.BR fork (2), +any thread should be able to +.BR wait (2) +on the child. +However, the implementation allows only the thread that +created the child to +.BR wait (2) +on it. +.IP \[bu] +When a thread calls +.BR execve (2), +all other threads are terminated (as required by POSIX.1). +However, the resulting process has the same PID as the thread that called +.BR execve (2): +it should have the same PID as the main thread. +.IP \[bu] +Threads do not share user and group IDs. +This can cause complications with set-user-ID programs and +can cause failures in Pthreads functions if an application +changes its credentials using +.BR seteuid (2) +or similar. +.IP \[bu] +Threads do not share a common session ID and process group ID. +.IP \[bu] +Threads do not share record locks created using +.BR fcntl (2). +.IP \[bu] +The information returned by +.BR times (2) +and +.BR getrusage (2) +is per-thread rather than process-wide. +.IP \[bu] +Threads do not share semaphore undo values (see +.BR semop (2)). +.IP \[bu] +Threads do not share interval timers. +.IP \[bu] +Threads do not share a common nice value. +.IP \[bu] +POSIX.1 distinguishes the notions of signals that are directed +to the process as a whole and signals that are directed to individual +threads. +According to POSIX.1, a process-directed signal (sent using +.BR kill (2), +for example) should be handled by a single, +arbitrarily selected thread within the process. +LinuxThreads does not support the notion of process-directed signals: +signals may be sent only to specific threads. +.IP \[bu] +Threads have distinct alternate signal stack settings. +However, a new thread's alternate signal stack settings +are copied from the thread that created it, so that +the threads initially share an alternate signal stack. +(A new thread should start with no alternate signal stack defined. +If two threads handle signals on their shared alternate signal +stack at the same time, unpredictable program failures are +likely to occur.) +.SS NPTL +With NPTL, all of the threads in a process are placed +in the same thread group; +all members of a thread group share the same PID. +NPTL does not employ a manager thread. +.PP +NPTL makes internal use of the first two real-time signals; +these signals cannot be used in applications. +See +.BR nptl (7) +for further details. +.PP +NPTL still has at least one nonconformance with POSIX.1: +.IP \[bu] 3 +Threads do not share a common nice value. +.\" FIXME . bug report filed for NPTL nice nonconformance +.\" http://bugzilla.kernel.org/show_bug.cgi?id=6258 +.\" Sep 08: there is a patch by Denys Vlasenko to address this +.\" "make setpriority POSIX compliant; introduce PRIO_THREAD extension" +.\" Monitor this to see if it makes it into mainline. +.PP +Some NPTL nonconformances occur only with older kernels: +.IP \[bu] 3 +The information returned by +.BR times (2) +and +.BR getrusage (2) +is per-thread rather than process-wide (fixed in Linux 2.6.9). +.IP \[bu] +Threads do not share resource limits (fixed in Linux 2.6.10). +.IP \[bu] +Threads do not share interval timers (fixed in Linux 2.6.12). +.IP \[bu] +Only the main thread is permitted to start a new session using +.BR setsid (2) +(fixed in Linux 2.6.16). +.IP \[bu] +Only the main thread is permitted to make the process into a +process group leader using +.BR setpgid (2) +(fixed in Linux 2.6.16). +.IP \[bu] +Threads have distinct alternate signal stack settings. +However, a new thread's alternate signal stack settings +are copied from the thread that created it, so that +the threads initially share an alternate signal stack +(fixed in Linux 2.6.16). +.PP +Note the following further points about the NPTL implementation: +.IP \[bu] 3 +If the stack size soft resource limit (see the description of +.B RLIMIT_STACK +in +.BR setrlimit (2)) +is set to a value other than +.IR unlimited , +then this value defines the default stack size for new threads. +To be effective, this limit must be set before the program +is executed, perhaps using the +.I ulimit \-s +shell built-in command +.RI ( "limit stacksize" +in the C shell). +.SS Determining the threading implementation +Since glibc 2.3.2, the +.BR getconf (1) +command can be used to determine +the system's threading implementation, for example: +.PP +.in +4n +.EX +bash$ getconf GNU_LIBPTHREAD_VERSION +NPTL 2.3.4 +.EE +.in +.PP +With older glibc versions, a command such as the following should +be sufficient to determine the default threading implementation: +.PP +.in +4n +.EX +bash$ $( ldd /bin/ls | grep libc.so | awk \[aq]{print $3}\[aq] ) | \e + egrep \-i \[aq]threads|nptl\[aq] + Native POSIX Threads Library by Ulrich Drepper et al +.EE +.in +.SS Selecting the threading implementation: LD_ASSUME_KERNEL +On systems with a glibc that supports both LinuxThreads and NPTL +(i.e., glibc 2.3.\fIx\fP), the +.B LD_ASSUME_KERNEL +environment variable can be used to override +the dynamic linker's default choice of threading implementation. +This variable tells the dynamic linker to assume that it is +running on top of a particular kernel version. +By specifying a kernel version that does not +provide the support required by NPTL, we can force the use +of LinuxThreads. +(The most likely reason for doing this is to run a +(broken) application that depends on some nonconformant behavior +in LinuxThreads.) +For example: +.PP +.in +4n +.EX +bash$ $( LD_ASSUME_KERNEL=2.2.5 ldd /bin/ls | grep libc.so | \e + awk \[aq]{print $3}\[aq] ) | egrep \-i \[aq]threads|nptl\[aq] + linuxthreads\-0.10 by Xavier Leroy +.EE +.in +.SH SEE ALSO +.ad l +.nh +.BR clone (2), +.BR fork (2), +.BR futex (2), +.BR gettid (2), +.BR proc (5), +.BR attributes (7), +.BR futex (7), +.BR nptl (7), +.BR sigevent (7), +.BR signal (7) +.PP +Various Pthreads manual pages, for example: +.BR pthread_atfork (3), +.BR pthread_attr_init (3), +.BR pthread_cancel (3), +.BR pthread_cleanup_push (3), +.BR pthread_cond_signal (3), +.BR pthread_cond_wait (3), +.BR pthread_create (3), +.BR pthread_detach (3), +.BR pthread_equal (3), +.BR pthread_exit (3), +.BR pthread_key_create (3), +.BR pthread_kill (3), +.BR pthread_mutex_lock (3), +.BR pthread_mutex_unlock (3), +.BR pthread_mutexattr_destroy (3), +.BR pthread_mutexattr_init (3), +.BR pthread_once (3), +.BR pthread_spin_init (3), +.BR pthread_spin_lock (3), +.BR pthread_rwlockattr_setkind_np (3), +.BR pthread_setcancelstate (3), +.BR pthread_setcanceltype (3), +.BR pthread_setspecific (3), +.BR pthread_sigmask (3), +.BR pthread_sigqueue (3), +and +.BR pthread_testcancel (3) |