threads.html

unix 下的C开发手册,还用详细的例程。

or
<i>disabled</i>
cancelability states.
<h5><a name = "tag_000_010_008_001">&nbsp;</a>Cancelability States</h5>
<p>
The cancelability state of a thread determines the action taken
upon receipt of a cancellation request.
The thread may control cancellation in a number of ways.
<p>
Each thread maintains its own cancelability state,
which may be encoded in two bits:
<dl compact>

<dt><i>Cancelability Enable</i><dd>
When cancelability is PTHREAD_CANCEL_DISABLE,
cancellation requests against the target thread are held pending.
By default, cancelability is set to PTHREAD_CANCEL_ENABLE.

<dt><i>Cancelability Type</i><dd>
When cancelability is enabled and the cancelability type is
PTHREAD_CANCEL_ASYNCHRONOUS,
new or pending cancellation requests may be acted upon at any time.
When cancelability is enabled and the cancelability type is
PTHREAD_CANCEL_DEFERRED,
cancellation requests are held pending until a cancellation point
(see below) is reached.
If cancelability is disabled,
the setting of the cancelability
type has no immediate effect as all cancellation requests are held pending,
however, once cancelability is enabled again the new type will be in effect.
The cancelability type is PTHREAD_CANCEL_DEFERRED
in all newly created threads including the thread in which
<i>main()</i>
was first invoked.

</dl>
<h5><a name = "tag_000_010_008_002">&nbsp;</a>Cancellation Points</h5>
<p>
Cancellation points occur
when a thread is executing the following functions:
<pre>
<i><a href="aio_suspend.html">aio_suspend()</a></i>
<i><a href="close.html">close()</a></i>
<i><a href="creat.html">creat()</a></i>
<i><a href="fcntl.html">fcntl()</a></i>
<i><a href="fsync.html">fsync()</a></i>
<i><a href="getmsg.html">getmsg()</a></i>
<i><a href="getpmsg.html">getpmsg()</a></i>
<i><a href="lockf.html">lockf()</a></i>
<i><a href="mq_receive.html">mq_receive()</a></i>
<i><a href="mq_send.html">mq_send()</a></i>
<i><a href="msgrcv.html">msgrcv()</a></i>
<i><a href="msgsnd.html">msgsnd()</a></i>
<i><a href="msync.html">msync()</a></i>
<i><a href="nanosleep.html">nanosleep()</a></i>
<i><a href="open.html">open()</a></i>
<i><a href="pause.html">pause()</a></i>
<i><a href="poll.html">poll()</a></i>
<i><a href="pread.html">pread()</a></i>
<i><a href="pthread_cond_timedwait.html">pthread_cond_timedwait()</a></i>
<i><a href="pthread_cond_wait.html">pthread_cond_wait()</a></i>
<i><a href="pthread_join.html">pthread_join()</a></i>
<i><a href="pthread_testcancel.html">pthread_testcancel()</a></i>
<i><a href="putmsg.html">putmsg()</a></i>
<i><a href="putpmsg.html">putpmsg()</a></i>
<i><a href="pwrite.html">pwrite()</a></i>
<i><a href="read.html">read()</a></i>
<i><a href="readv.html">readv()</a></i>
<i><a href="select.html">select()</a></i>
<i><a href="sem_wait.html">sem_wait()</a></i>
<i><a href="sigpause.html">sigpause()</a></i>
<i><a href="sigsuspend.html">sigsuspend()</a></i>
<i><a href="sigtimedwait.html">sigtimedwait()</a></i>
<i><a href="sigwait.html">sigwait()</a></i>
<i><a href="sigwaitinfo.html">sigwaitinfo()</a></i>
<i><a href="sleep.html">sleep()</a></i>
<i><a href="system.html">system()</a></i>
<i><a href="tcdrain.html">tcdrain()</a></i>
<i><a href="usleep.html">usleep()</a></i>
<i><a href="wait.html">wait()</a></i>
<i><a href="wait3.html">wait3()</a></i>
<i><a href="waitid.html">waitid()</a></i>
<i><a href="waitpid.html">waitpid()</a></i>
<i><a href="write.html">write()</a></i>
<i><a href="writev.html">writev()</a></i>
</pre>
<p>
<p>
A cancellation point may also occur
when a thread is executing the following functions:
<p>
<pre>
<i><a href="catclose.html">catclose()</a></i>
<i><a href="catgets.html">catgets()</a></i>
<i><a href="catopen.html">catopen()</a></i>
<i><a href="closedir.html">closedir()</a></i>
<i><a href="closelog.html">closelog()</a></i>
<i><a href="ctermid.html">ctermid()</a></i>
<i><a href="dbm_close.html">dbm_close()</a></i>
<i><a href="dbm_delete.html">dbm_delete()</a></i>
<i><a href="dbm_fetch.html">dbm_fetch()</a></i>
<i><a href="dbm_nextkey.html">dbm_nextkey()</a></i>
<i><a href="dbm_open.html">dbm_open()</a></i>
<i><a href="dbm_store.html">dbm_store()</a></i>
<i><a href="dlclose.html">dlclose()</a></i>
<i><a href="dlopen.html">dlopen()</a></i>
<i><a href="endgrent.html">endgrent()</a></i>
<i><a href="endpwent.html">endpwent()</a></i>
<i><a href="endutxent.html">endutxent()</a></i>
<i><a href="fclose.html">fclose()</a></i>
<i><a href="fcntl.html">fcntl()</a></i>
<i><a href="fflush.html">fflush()</a></i>
<i><a href="fgetc.html">fgetc()</a></i>
<i><a href="fgetpos.html">fgetpos()</a></i>
<i><a href="fgets.html">fgets()</a></i>
<i><a href="fgetwc.html">fgetwc()</a></i>
<i><a href="fgetws.html">fgetws()</a></i>
<i><a href="fopen.html">fopen()</a></i>
<i><a href="fprintf.html">fprintf()</a></i>
<i><a href="fputc.html">fputc()</a></i>
<i><a href="fputs.html">fputs()</a></i>
<i><a href="fputwc.html">fputwc()</a></i>
<i><a href="fputws.html">fputws()</a></i>
<i><a href="fread.html">fread()</a></i>
<i><a href="freopen.html">freopen()</a></i>
<i><a href="fscanf.html">fscanf()</a></i>
<i><a href="fseek.html">fseek()</a></i>
<i><a href="fseeko.html">fseeko()</a></i>
<i><a href="fsetpos.html">fsetpos()</a></i>
<i><a href="ftell.html">ftell()</a></i>
<i><a href="ftello.html">ftello()</a></i>
<i><a href="ftw.html">ftw()</a></i>
<i><a href="fwprintf.html">fwprintf()</a></i>
<i><a href="fwrite.html">fwrite()</a></i>
<i><a href="fwscanf.html">fwscanf()</a></i>
<i><a href="getc.html">getc()</a></i>
<i><a href="getc_unlocked.html">getc_unlocked()</a></i>
<i><a href="getchar.html">getchar()</a></i>
<i><a href="getchar_unlocked.html">getchar_unlocked()</a></i>
<i><a href="getcwd.html">getcwd()</a></i>
<i><a href="getdate.html">getdate()</a></i>
<i><a href="getgrent.html">getgrent()</a></i>
<i><a href="getgrgid.html">getgrgid()</a></i>
<i><a href="getgrgid.html">getgrgid_r()</a></i>
<i><a href="getgrnam.html">getgrnam()</a></i>
<i><a href="getgrnam.html">getgrnam_r()</a></i>
<i><a href="getlogin.html">getlogin()</a></i>
<i><a href="getlogin.html">getlogin_r()</a></i>
<i><a href="getpwent.html">getpwent()</a></i>
<i><a href="getpwnam.html">getpwnam()</a></i>
<i><a href="getpwnam.html">getpwnam_r()</a></i>
<i><a href="getpwuid.html">getpwuid()</a></i>
<i><a href="getpwuid.html">getpwuid_r()</a></i>
<i><a href="gets.html">gets()</a></i>
<i><a href="getutxent.html">getutxent()</a></i>
<i><a href="getutxid.html">getutxid()</a></i>
<i><a href="getutxline.html">getutxline()</a></i>
<i><a href="getw.html">getw()</a></i>
<i><a href="getwc.html">getwc()</a></i>
<i><a href="getwchar.html">getwchar()</a></i>
<i><a href="getwd.html">getwd()</a></i>
<i><a href="glob.html">glob()</a></i>
<i><a href="iconv_close.html">iconv_close()</a></i>
<i><a href="iconv_open.html">iconv_open()</a></i>
<i><a href="ioctl.html">ioctl()</a></i>
<i><a href="lseek.html">lseek()</a></i>
<i><a href="mkstemp.html">mkstemp()</a></i>
<i><a href="nftw.html">nftw()</a></i>
<i><a href="opendir.html">opendir()</a></i>
<i><a href="openlog.html">openlog()</a></i>
<i><a href="pclose.html">pclose()</a></i>
<i><a href="perror.html">perror()</a></i>
<i><a href="popen.html">popen()</a></i>
<i><a href="printf.html">printf()</a></i>
<i><a href="putc.html">putc()</a></i>
<i><a href="putc_unlocked.html">putc_unlocked()</a></i>
<i><a href="putchar.html">putchar()</a></i>
<i><a href="putchar_unlocked.html">putchar_unlocked()</a></i>
<i><a href="puts.html">puts()</a></i>
<i><a href="pututxline.html">pututxline()</a></i>
<i><a href="putw.html">putw()</a></i>
<i><a href="putwc.html">putwc()</a></i>
<i><a href="putwchar.html">putwchar()</a></i>
<i><a href="readdir.html">readdir()</a></i>
<i><a href="readdir.html">readdir_r()</a></i>
<i><a href="remove.html">remove()</a></i>
<i><a href="rename.html">rename()</a></i>
<i><a href="rewind.html">rewind()</a></i>
<i><a href="rewinddir.html">rewinddir()</a></i>
<i><a href="scanf.html">scanf()</a></i>
<i><a href="seekdir.html">seekdir()</a></i>
<i><a href="semop.html">semop()</a></i>
<i><a href="setgrent.html">setgrent()</a></i>
<i><a href="setpwent.html">setpwent()</a></i>
<i><a href="setutxent.html">setutxent()</a></i>
<i><a href="strerror.html">strerror()</a></i>
<i><a href="syslog.html">syslog()</a></i>
<i><a href="tmpfile.html">tmpfile()</a></i>
<i><a href="tmpnam.html">tmpnam()</a></i>
<i><a href="ttyname.html">ttyname()</a></i>
<i><a href="ttyname.html">ttyname_r()</a></i>
<i><a href="ungetc.html">ungetc()</a></i>
<i><a href="ungetwc.html">ungetwc()</a></i>
<i><a href="unlink.html">unlink()</a></i>
<i><a href="vfprintf.html">vfprintf()</a></i>
<i><a href="vfwprintf.html">vfwprintf()</a></i>
<i><a href="vprintf.html">vprintf()</a></i>
<i><a href="vwprintf.html">vwprintf()</a></i>
<i><a href="wprintf.html">wprintf()</a></i>
<i><a href="wscanf.html">wscanf()</a></i>
</pre>
<p>
Note, that for
<i><a href="fcntl.html">fcntl()</a></i>,
for any value of the
<i>cmd</i>
argument.
<p>
An implementation will not introduce cancellation points
into any other functions specified in this specification.
<p>
The side effects of acting upon a cancellation request
while suspended during a call of a function
is the same as the side effects
that may be seen in a single-threaded program
when a call to a function is interrupted by a signal
and the given function returns [EINTR].
Any such side effects occur before any
cancellation cleanup handlers are called.
<p>
Whenever a thread has cancelability enabled
and a cancellation request has been made with that thread as the target
and the thread calls
<i><a href="pthread_testcancel.html">pthread_testcancel()</a></i>,
then the cancellation request is acted upon before
<i><a href="pthread_testcancel.html">pthread_testcancel()</a></i>
returns.
If a thread has cancelability enabled
and the thread has an asynchronous cancellation request pending and
the thread is suspended at a cancellation point waiting for an event to occur,
then the cancellation request will be acted upon.
However, if the thread is suspended at a cancellation point
and the event that it is waiting for occurs
before the cancellation request is acted upon, it is
unspecified whether the cancellation request is acted upon
or whether the request remains pending and the thread resumes normal execution.
<h5><a name = "tag_000_010_008_003">&nbsp;</a>Thread Cancellation Cleanup Handlers</h5>
<p>
Each thread maintains a list of cancellation cleanup handlers.
The programmer uses the functions
<i><a href="pthread_cleanup_push.html">pthread_cleanup_push()</a></i>
and
<i><a href="pthread_cleanup_pop.html">pthread_cleanup_pop()</a></i>
to place routines on and remove routines from this list.
<p>
When a cancellation request is acted upon,
the routines in the list are invoked one by one in LIFO
sequence; that is, the last routine pushed onto the list (Last In)
is the first to be invoked (First Out).
The thread invokes the cancellation cleanup handler
with cancellation disabled until the last
cancellation cleanup handler returns.
When the cancellation cleanup handler
for a scope is invoked,
the storage for that scope remains valid.
If the last cancellation cleanup handler
returns, thread execution is terminated
and a status of PTHREAD_CANCELED
is made available to any threads joining with the target.
The symbolic constant PTHREAD_CANCELED
expands to a constant expression of type (<b> void *</b>)
whose value matches no pointer to an object in memory nor the value NULL.
<p>
The cancellation cleanup handlers
are also invoked when the thread calls
<i><a href="pthread_exit.html">pthread_exit()</a></i>.
<p>
A side effect of acting upon a cancellation request
while in a condition variable wait is that
the mutex is reacquired before calling the first
cancellation cleanup handler.
In addition,
the thread is no longer considered to be waiting for the condition
and the thread will not have consumed any pending
condition signals
on the condition.
<p>
A cancellation cleanup handler cannot exit via
<i><a href="longjmp.html">longjmp()</a></i>
or
<i><a href="siglongjmp.html">siglongjmp()</a></i>.
<h5><a name = "tag_000_010_008_004">&nbsp;</a>Async-Cancel Safety</h5>
The
<i><a href="pthread_cancel.html">pthread_cancel()</a></i>,
<i><a href="pthread_setcancelstate.html">pthread_setcancelstate()</a></i>
and
<i><a href="pthread_setcanceltype.html">pthread_setcanceltype()</a></i>
functions are defined to be async-cancel safe.
<p>
No other functions in this specification
are required to be async-cancel safe.
<h4><a name = "tag_000_010_009">&nbsp;</a>Thread Read-Write Locks</h4>
<p>
Multiple readers, single writer (read-write) locks allow many
threads  to have simultaneous read-only access to data
while allowing only one thread to have write access at any given
time.  They are typically used to protect data that is read-only
more frequently than it is changed.
<p>
Read-write locks can be used to synchronise threads in the current
process and other processes if they are allocated in memory that
is writable and shared among the cooperating processes and have been
initialised for this behaviour.
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