pthreads手册
原文地址：http://man7.org/linux/man-pages/man7/pthreads.7.html
PTHREADS(7) Linux Programmer's Manual PTHREADS(7)
NAME top
pthreads - POSIX threads
DESCRIPTION top
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).
POSIX.1 also requires that threads share a range of other attributes
(i.e., these attributes are process-wide rather than per-thread):
- process ID
- parent process ID
- process group ID and session ID
- controlling terminal
- user and group IDs
- open file descriptors
- record locks (see fcntl(2))
- signal dispositions
- file mode creation mask (umask(2))
- current directory (chdir(2)) and root directory (chroot(2))
- interval timers (setitimer(2)) and POSIX timers (timer_create(2))
- nice value (setpriority(2))
- resource limits (setrlimit(2))
- measurements of the consumption of CPU time (times(2)) and
resources (getrusage(2))
As well as the stack, POSIX.1 specifies that various other attributes
are distinct for each thread, including:
- thread ID (the pthread_t data type)
- signal mask (pthread_sigmask(3))
- the errno variable
- alternate signal stack (sigaltstack(2))
- real-time scheduling policy and priority (sched_setscheduler(2)
and sched_setparam(2))
The following Linux-specific features are also per-thread:
- capabilities (see capabilities(7))
- CPU affinity (sched_setaffinity(2))
Pthreads function return values
Most pthreads functions return 0 on success, and an error number of
failure. Note that the pthreads functions do not set 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 EINTR.
Thread IDs
Each of the threads in a process has a unique thread identifier
(stored in the type pthread_t). This identifier is returned to the
caller of pthread_create(3), and a thread can obtain its own thread
identifier using pthread_self(3). Thread IDs are guaranteed to be
unique only within a process. A thread ID may be reused after a
terminated thread has been joined, or a detached thread has
terminated. 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.
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.
POSIX.1-2001 and POSIX.1-2008 require that all functions specified in
the standard shall be thread-safe, except for the following
functions:
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()
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
pthread_setcancelstate(3)).
Only the following functions are required to be async-cancel-safe by
POSIX.1-2001 and POSIX.1-2008:
pthread_cancel()
pthread_setcancelstate()
pthread_setcanceltype()
Cancellation points
POSIX.1 specifies that certain functions must, and certain other
functions may, be cancellation points. If a thread is cancelable,
its cancelability type is deferred, and a cancellation request is
pending for the thread, then the thread is canceled when it calls a
function that is a cancellation point.
The following functions are required to be cancellation points by
POSIX.1-2001 and/or POSIX.1-2008:
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()
The following functions may be cancellation points according to
POSIX.1-2001 and/or POSIX.1-2008:
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() [SUSv3 only (function removed in POSIX.1-2008)]
gethostbyname() [SUSv3 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() [SUSv3 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()
An implementation may also mark other functions not specified in the
standard as cancellation points. In particular, an implementation is
likely to mark any nonstandard function that may block as a
cancellation point. (This includes most functions that can touch
files.)
Compiling on Linux
On Linux, programs that use the Pthreads API should be compiled using
cc -pthread.
Linux implementations of POSIX threads
Over time, two threading implementations have been provided by the
GNU C library on Linux:
LinuxThreads
This is the original Pthreads implementation. Since glibc
2.4, this implementation is no longer supported.
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.
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 clone(2) system call. In NPTL,
thread synchronization primitives (mutexes, thread joining, and so
on) are implemented using the Linux futex(2) system call.
LinuxThreads
The notable features of this implementation are the following:
- In addition to the main (initial) thread, and the threads that the
program creates using 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.)
- Signals are used internally by the implementation. On Linux 2.2
and later, the first three real-time signals are used (see also
signal(7)). On older Linux kernels, SIGUSR1 and SIGUSR2 are used.
Applications must avoid the use of whichever set of signals is
employed by the implementation.
- 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 ps(1).
The LinuxThreads implementation deviates from the POSIX.1
specification in a number of ways, including the following:
- Calls to getpid(2) return a different value in each thread.
- Calls to getppid(2) in threads other than the main thread return
the process ID of the manager thread; instead getppid(2) in these
threads should return the same value as getppid(2) in the main
thread.
- When one thread creates a new child process using fork(2), any
thread should be able to wait(2) on the child. However, the
implementation only allows the thread that created the child to
wait(2) on it.
- When a thread calls 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 execve(2): it should have the
same PID as the main thread.
- 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
seteuid(2) or similar.
- Threads do not share a common session ID and process group ID.
- Threads do not share record locks created using fcntl(2).
- The information returned by times(2) and getrusage(2) is per-
thread rather than process-wide.
- Threads do not share semaphore undo values (see semop(2)).
- Threads do not share interval timers.
- Threads do not share a common nice value.
- 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 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.
- 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.)
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. NPTL makes internal use of the
first two real-time signals (see also signal(7)); these signals
cannot be used in applications.
NPTL still has at least one nonconformance with POSIX.1:
- Threads do not share a common nice value.
Some NPTL nonconformances occur only with older kernels:
- The information returned by times(2) and getrusage(2) is per-
thread rather than process-wide (fixed in kernel 2.6.9).
- Threads do not share resource limits (fixed in kernel 2.6.10).
- Threads do not share interval timers (fixed in kernel 2.6.12).
- Only the main thread is permitted to start a new session using
setsid(2) (fixed in kernel 2.6.16).
- Only the main thread is permitted to make the process into a
process group leader using setpgid(2) (fixed in kernel 2.6.16).
- 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 kernel 2.6.16).
Note the following further points about the NPTL implementation:
- If the stack size soft resource limit (see the description of
RLIMIT_STACK in setrlimit(2)) is set to a value other than
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 ulimit -s shell built-in
command (limit stacksize in the C shell).
Determining the threading implementation
Since glibc 2.3.2, the getconf(1) command can be used to determine
the system's threading implementation, for example:
bash$ getconf GNU_LIBPTHREAD_VERSION
NPTL 2.3.4
With older glibc versions, a command such as the following should be
sufficient to determine the default threading implementation:
bash$ $( ldd /bin/ls | grep libc.so | awk '{print $3}' ) | \
egrep -i 'threads|nptl'
Native POSIX Threads Library by Ulrich Drepper et al
Selecting the threading implementation: LD_ASSUME_KERNEL
On systems with a glibc that supports both LinuxThreads and NPTL
(i.e., glibc 2.3.x), the LD_ASSUME_KERNEL environment variable can be
used to override the dynamic linker's default choice of threading
implementation. This variable tells the dynamic linker to assume
that it is running on top of a particular kernel version. By
specifying a kernel version that does not provide the support
required by NPTL, we can force the use of LinuxThreads. (The most
likely reason for doing this is to run a (broken) application that
depends on some nonconformant behavior in LinuxThreads.) For
example:
bash$ $( LD_ASSUME_KERNEL=2.2.5 ldd /bin/ls | grep libc.so | \
awk '{print $3}' ) | egrep -i 'threads|ntpl'
linuxthreads-0.10 by Xavier Leroy
SEE ALSO top
clone(2), futex(2), gettid(2), proc(5), futex(7), sigevent(7), signal(7), Various Pthreads manual pages, for example: pthread_attr_init(3), pthread_atfork(3), pthread_cancel(3), pthread_cleanup_push(3), pthread_cond_signal(3), pthread_cond_wait(3), pthread_create(3), pthread_detach(3), pthread_equal(3), pthread_exit(3), pthread_key_create(3), pthread_kill(3), pthread_mutex_lock(3), pthread_mutex_unlock(3), pthread_once(3), pthread_setcancelstate(3), pthread_setcanceltype(3), pthread_setspecific(3), pthread_sigmask(3), pthread_sigqueue(3), and pthread_testcancel(3)
COLOPHON top
This page is part of release 3.51 of the Linux man-pages project. A
description of the project, and information about reporting bugs, can
be found at http://www.kernel.org/doc/man-pages/.
Linux 2010-11-14 PTHREADS(7)