ptthread.c

Netscape NSPR库源码

static void suspend_signal_handler(PRIntn sig);

#ifdef PT_NO_SIGTIMEDWAIT
static void null_signal_handler(PRIntn sig);
#endif

#endif /* defined(_PR_DCETHREADS) */

/*
 * Linux pthreads use SIGUSR1 and SIGUSR2 internally, which
 * conflict with the use of these two signals in our GC support.
 * So we don't know how to support GC on Linux pthreads.
 */
static void init_pthread_gc_support(void)
{
    PRIntn rv;

#if defined(_PR_DCETHREADS)
	rv = sigemptyset(&javagc_vtalarm_sigmask);
    PR_ASSERT(0 == rv);
	rv = sigaddset(&javagc_vtalarm_sigmask, SIGVTALRM);
    PR_ASSERT(0 == rv);
#else  /* defined(_PR_DCETHREADS) */
	{
	    struct sigaction sigact_usr2;

	    sigact_usr2.sa_handler = suspend_signal_handler;
	    sigact_usr2.sa_flags = SA_RESTART;
	    sigemptyset (&sigact_usr2.sa_mask);

        rv = sigaction (SIGUSR2, &sigact_usr2, NULL);
        PR_ASSERT(0 == rv);

        sigemptyset (&sigwait_set);
#if defined(PT_NO_SIGTIMEDWAIT)
        sigaddset (&sigwait_set, SIGUSR1);
#else
        sigaddset (&sigwait_set, SIGUSR2);
#endif  /* defined(PT_NO_SIGTIMEDWAIT) */
	}
#if defined(PT_NO_SIGTIMEDWAIT)
	{
	    struct sigaction sigact_null;
	    sigact_null.sa_handler = null_signal_handler;
	    sigact_null.sa_flags = SA_RESTART;
	    sigemptyset (&sigact_null.sa_mask);
        rv = sigaction (SIGUSR1, &sigact_null, NULL);
	    PR_ASSERT(0 ==rv); 
    }
#endif  /* defined(PT_NO_SIGTIMEDWAIT) */
#endif /* defined(_PR_DCETHREADS) */
}

PR_IMPLEMENT(void) PR_SetThreadGCAble(void)
{
    PR_Lock(pt_book.ml);
	PR_CurrentThread()->state |= PT_THREAD_GCABLE;
    PR_Unlock(pt_book.ml);
}

PR_IMPLEMENT(void) PR_ClearThreadGCAble(void)
{
    PR_Lock(pt_book.ml);
	PR_CurrentThread()->state &= (~PT_THREAD_GCABLE);
    PR_Unlock(pt_book.ml);
}

#if defined(DEBUG)
static PRBool suspendAllOn = PR_FALSE;
#endif

static PRBool suspendAllSuspended = PR_FALSE;

PR_IMPLEMENT(PRStatus) PR_EnumerateThreads(PREnumerator func, void *arg)
{
    PRIntn count = 0;
    PRStatus rv = PR_SUCCESS;
    PRThread* thred = pt_book.first;
    PRThread *me = PR_CurrentThread();

    PR_LOG(_pr_gc_lm, PR_LOG_ALWAYS, ("Begin PR_EnumerateThreads\n"));
    /*
     * $$$
     * Need to suspend all threads other than me before doing this.
     * This is really a gross and disgusting thing to do. The only
     * good thing is that since all other threads are suspended, holding
     * the lock during a callback seems like child's play.
     * $$$
     */
    PR_ASSERT(suspendAllOn);

    while (thred != NULL)
    {
        /* Steve Morse, 4-23-97: Note that we can't walk a queue by taking
         * qp->next after applying the function "func".  In particular, "func"
         * might remove the thread from the queue and put it into another one in
         * which case qp->next no longer points to the next entry in the original
         * queue.
         *
         * To get around this problem, we save qp->next in qp_next before applying
         * "func" and use that saved value as the next value after applying "func".
         */
        PRThread* next = thred->next;

        if (_PT_IS_GCABLE_THREAD(thred))
        {
#if !defined(_PR_DCETHREADS)
            PR_ASSERT((thred == me) || (thred->suspend & PT_THREAD_SUSPENDED));
#endif
            PR_LOG(_pr_gc_lm, PR_LOG_ALWAYS, 
                   ("In PR_EnumerateThreads callback thread %X thid = %X\n", 
                    thred, thred->id));

            rv = func(thred, count++, arg);
            if (rv != PR_SUCCESS)
                return rv;
        }
        thred = next;
    }
    PR_LOG(_pr_gc_lm, PR_LOG_ALWAYS, 
	   ("End PR_EnumerateThreads count = %d \n", count));
    return rv;
}  /* PR_EnumerateThreads */

/*
 * PR_SuspendAll and PR_ResumeAll are called during garbage collection.  The strategy 
 * we use is to send a SIGUSR2 signal to every gc able thread that we intend to suspend.
 * The signal handler will record the stack pointer and will block until resumed by
 * the resume call.  Since the signal handler is the last routine called for the
 * suspended thread, the stack pointer will also serve as a place where all the
 * registers have been saved on the stack for the previously executing routines.
 *
 * Through global variables, we also make sure that PR_Suspend and PR_Resume does not
 * proceed until the thread is suspended or resumed.
 */

#if !defined(_PR_DCETHREADS)

/*
 * In the signal handler, we can not use condition variable notify or wait.
 * This does not work consistently across all pthread platforms.  We also can not 
 * use locking since that does not seem to work reliably across platforms.
 * Only thing we can do is yielding while testing for a global condition
 * to change.  This does work on pthread supported platforms.  We may have
 * to play with priortities if there are any problems detected.
 */

 /* 
  * In AIX, you cannot use ANY pthread calls in the signal handler except perhaps
  * pthread_yield. But that is horribly inefficient. Hence we use only sigwait, no
  * sigtimedwait is available. We need to use another user signal, SIGUSR1. Actually
  * SIGUSR1 is also used by exec in Java. So our usage here breaks the exec in Java,
  * for AIX. You cannot use pthread_cond_wait or pthread_delay_np in the signal
  * handler as all synchronization mechanisms just break down. 
  */

#if defined(PT_NO_SIGTIMEDWAIT)
static void null_signal_handler(PRIntn sig)
{
	return;
}
#endif

static void suspend_signal_handler(PRIntn sig)
{
	PRThread *me = PR_CurrentThread();

	PR_ASSERT(me != NULL);
	PR_ASSERT(_PT_IS_GCABLE_THREAD(me));
	PR_ASSERT((me->suspend & PT_THREAD_SUSPENDED) == 0);

	PR_LOG(_pr_gc_lm, PR_LOG_ALWAYS, 
        ("Begin suspend_signal_handler thred %X thread id = %X\n", 
		me, me->id));

	/*
	 * save stack pointer
	 */
	me->sp = &me;

	/* 
	   At this point, the thread's stack pointer has been saved,
	   And it is going to enter a wait loop until it is resumed.
	   So it is _really_ suspended 
	*/

	me->suspend |= PT_THREAD_SUSPENDED;

	/*
	 * now, block current thread
	 */
#if defined(PT_NO_SIGTIMEDWAIT)
	pthread_cond_signal(&me->suspendResumeCV);
	while (me->suspend & PT_THREAD_SUSPENDED)
	{
#if !defined(FREEBSD) && !defined(NETBSD) && !defined(OPENBSD) \
    && !defined(BSDI) && !defined(VMS) && !defined(UNIXWARE) && !defined(DARWIN)  /*XXX*/
        PRIntn rv;
	    sigwait(&sigwait_set, &rv);
#endif
	}
	me->suspend |= PT_THREAD_RESUMED;
	pthread_cond_signal(&me->suspendResumeCV);
#else /* defined(PT_NO_SIGTIMEDWAIT) */
	while (me->suspend & PT_THREAD_SUSPENDED)
	{
		PRIntn rv = sigtimedwait(&sigwait_set, NULL, &hundredmillisec);
    	PR_ASSERT(-1 == rv);
	}
	me->suspend |= PT_THREAD_RESUMED;
#endif

    /*
     * At this point, thread has been resumed, so set a global condition.
     * The ResumeAll needs to know that this has really been resumed. 
     * So the signal handler sets a flag which PR_ResumeAll will reset. 
     * The PR_ResumeAll must reset this flag ...
     */

    PR_LOG(_pr_gc_lm, PR_LOG_ALWAYS, 
        ("End suspend_signal_handler thred = %X tid = %X\n", me, me->id));
}  /* suspend_signal_handler */

static void pt_SuspendSet(PRThread *thred)
{
    PRIntn rv;

    PR_LOG(_pr_gc_lm, PR_LOG_ALWAYS, 
	   ("pt_SuspendSet thred %X thread id = %X\n", thred, thred->id));


    /*
     * Check the thread state and signal the thread to suspend
     */

    PR_ASSERT((thred->suspend & PT_THREAD_SUSPENDED) == 0);

    PR_LOG(_pr_gc_lm, PR_LOG_ALWAYS, 
	   ("doing pthread_kill in pt_SuspendSet thred %X tid = %X\n",
	   thred, thred->id));
#if defined(VMS)
    rv = thread_suspend(thred);
#else
    rv = pthread_kill (thred->id, SIGUSR2);
#endif
    PR_ASSERT(0 == rv);
}

static void pt_SuspendTest(PRThread *thred)
{
    PR_LOG(_pr_gc_lm, PR_LOG_ALWAYS, 
	   ("Begin pt_SuspendTest thred %X thread id = %X\n", thred, thred->id));


    /*
     * Wait for the thread to be really suspended. This happens when the
     * suspend signal handler stores the stack pointer and sets the state
     * to suspended. 
     */

#if defined(PT_NO_SIGTIMEDWAIT)
    pthread_mutex_lock(&thred->suspendResumeMutex);
    while ((thred->suspend & PT_THREAD_SUSPENDED) == 0)
    {
	    pthread_cond_timedwait(
	        &thred->suspendResumeCV, &thred->suspendResumeMutex, &onemillisec);
	}
	pthread_mutex_unlock(&thred->suspendResumeMutex);
#else
    while ((thred->suspend & PT_THREAD_SUSPENDED) == 0)
    {
		PRIntn rv = sigtimedwait(&sigwait_set, NULL, &onemillisec);
    	PR_ASSERT(-1 == rv);
	}
#endif

    PR_LOG(_pr_gc_lm, PR_LOG_ALWAYS,
        ("End pt_SuspendTest thred %X tid %X\n", thred, thred->id));
}  /* pt_SuspendTest */

static void pt_ResumeSet(PRThread *thred)
{
    PR_LOG(_pr_gc_lm, PR_LOG_ALWAYS, 
	   ("pt_ResumeSet thred %X thread id = %X\n", thred, thred->id));

    /*
     * Clear the global state and set the thread state so that it will
     * continue past yield loop in the suspend signal handler
     */

    PR_ASSERT(thred->suspend & PT_THREAD_SUSPENDED);


    thred->suspend &= ~PT_THREAD_SUSPENDED;

#if defined(PT_NO_SIGTIMEDWAIT)
#if defined(VMS)
	thread_resume(thred);
#else
	pthread_kill(thred->id, SIGUSR1);
#endif
#endif

}  /* pt_ResumeSet */

static void pt_ResumeTest(PRThread *thred)
{
    PR_LOG(_pr_gc_lm, PR_LOG_ALWAYS, 
	   ("Begin pt_ResumeTest thred %X thread id = %X\n", thred, thred->id));

    /*
     * Wait for the threads resume state to change
     * to indicate it is really resumed 
     */
#if defined(PT_NO_SIGTIMEDWAIT)
    pthread_mutex_lock(&thred->suspendResumeMutex);
    while ((thred->suspend & PT_THREAD_RESUMED) == 0)
    {
	    pthread_cond_timedwait(
	        &thred->suspendResumeCV, &thred->suspendResumeMutex, &onemillisec);
    }
    pthread_mutex_unlock(&thred->suspendResumeMutex);
#else
    while ((thred->suspend & PT_THREAD_RESUMED) == 0) {
		PRIntn rv = sigtimedwait(&sigwait_set, NULL, &onemillisec);
    	PR_ASSERT(-1 == rv);
	}
#endif

    thred->suspend &= ~PT_THREAD_RESUMED;

    PR_LOG(_pr_gc_lm, PR_LOG_ALWAYS, (
        "End pt_ResumeTest thred %X tid %X\n", thred, thred->id));
}  /* pt_ResumeTest */

static pthread_once_t pt_gc_support_control = PTHREAD_ONCE_INIT;

PR_IMPLEMENT(void) PR_SuspendAll(void)
{
#ifdef DEBUG
    PRIntervalTime stime, etime;
#endif
    PRThread* thred = pt_book.first;
    PRThread *me = PR_CurrentThread();
    int rv;

    rv = pthread_once(&pt_gc_support_control, init_pthread_gc_support);
    PR_ASSERT(0 == rv);
    PR_LOG(_pr_gc_lm, PR_LOG_ALWAYS, ("Begin PR_SuspendAll\n"));
    /*
     * Stop all threads which are marked GC able.
     */
    PR_Lock(pt_book.ml);
#ifdef DEBUG
    suspendAllOn = PR_TRUE;
    stime = PR_IntervalNow();
#endif
    while (thred != NULL)
    {
	    if ((thred != me) && _PT_IS_GCABLE_THREAD(thred))
    		pt_SuspendSet(thred);
        thred = thred->next;
    }

    /* Wait till they are really suspended */
    thred = pt_book.first;
    while (thred != NULL)
    {
	    if ((thred != me) && _PT_IS_GCABLE_THREAD(thred))
            pt_SuspendTest(thred);
        thred = thred->next;
    }

    suspendAllSuspended = PR_TRUE;

#ifdef DEBUG
    etime = PR_IntervalNow();
    PR_LOG(_pr_gc_lm, PR_LOG_ALWAYS,\
        ("End PR_SuspendAll (time %dms)\n",
        PR_IntervalToMilliseconds(etime - stime)));
#endif
}  /* PR_SuspendAll */

PR_IMPLEMENT(void) PR_ResumeAll(void)
{
#ifdef DEBUG
    PRIntervalTime stime, etime;
#endif
    PRThread* thred = pt_book.first;
    PRThread *me = PR_CurrentThread();
    PR_LOG(_pr_gc_lm, PR_LOG_ALWAYS, ("Begin PR_ResumeAll\n"));
    /*
     * Resume all previously suspended GC able threads.
     */
    suspendAllSuspended = PR_FALSE;
#ifdef DEBUG
    stime = PR_IntervalNow();
#endif

    while (thred != NULL)
    {
	    if ((thred != me) && _PT_IS_GCABLE_THREAD(thred))
    	    pt_ResumeSet(thred);
        thred = thred->next;
    }

    thred = pt_book.first;
    while (thred != NULL)
    {
	    if ((thred != me) && _PT_IS_GCABLE_THREAD(thred))
    	    pt_ResumeTest(thred);
        thred = thred->next;
    }

    PR_Unlock(pt_book.ml);
#ifdef DEBUG
    suspendAllOn = PR_FALSE;
    etime = PR_IntervalNow();
    PR_LOG(_pr_gc_lm, PR_LOG_ALWAYS,
        ("End PR_ResumeAll (time %dms)\n",
        PR_IntervalToMilliseconds(etime - stime)));
#endif
}  /* PR_ResumeAll */

/* Return the stack pointer for the given thread- used by the GC */
PR_IMPLEMENT(void *)PR_GetSP(PRThread *thred)
{
    PR_LOG(_pr_gc_lm, PR_LOG_ALWAYS, 
	    ("in PR_GetSP thred %X thid = %X, sp = %X \n", 
	    thred, thred->id, thred->sp));
    return thred->sp;
}  /* PR_GetSP */

#else /* !defined(_PR_DCETHREADS) */

static pthread_once_t pt_gc_support_control = pthread_once_init;

/*
 * For DCE threads, there is no pthread_kill or a way of suspending or resuming a
 * particular thread.  We will just disable the preemption (virtual timer alarm) and
 * let the executing thread finish the garbage collection.  This stops all other threads
 * (GC able or not) and is very inefficient but there is no other choice.
 */
PR_IMPLEMENT(void) PR_SuspendAll()
{
    PRIntn rv;

    rv = pthread_once(&pt_gc_support_control, init_pthread_gc_support);
    PR_ASSERT(0 == rv);  /* returns -1 on failure */
#ifdef DEBUG
    suspendAllOn = PR_TRUE;
#endif
    PR_LOG(_pr_gc_lm, PR_LOG_ALWAYS, ("Begin PR_SuspendAll\n"));
    /* 
     * turn off preemption - i.e add virtual alarm signal to the set of 
     * blocking signals 
     */
    rv = sigprocmask(
        SIG_BLOCK, &javagc_vtalarm_sigmask, &javagc_intsoff_sigmask);
    PR_ASSERT(0 == rv);
    suspendAllSuspended = PR_TRUE;
    PR_LOG(_pr_gc_lm, PR_LOG_ALWAYS, ("End PR_SuspendAll\n"));
}  /* PR_SuspendAll */

PR_IMPLEMENT(void) PR_ResumeAll()
{
    PRIntn rv;
    
    suspendAllSuspended = PR_FALSE;
    PR_LOG(_pr_gc_lm, PR_LOG_ALWAYS, ("Begin PR_ResumeAll\n"));
    /* turn on preemption - i.e re-enable virtual alarm signal */

    rv = sigprocmask(SIG_SETMASK, &javagc_intsoff_sigmask, (sigset_t *)NULL);
    PR_ASSERT(0 == rv);
#ifdef DEBUG
    suspendAllOn = PR_FALSE;
#endif

    PR_LOG(_pr_gc_lm, PR_LOG_ALWAYS, ("End PR_ResumeAll\n"));
}  /* PR_ResumeAll */

/* Return the stack pointer for the given thread- used by the GC */
PR_IMPLEMENT(void*)PR_GetSP(PRThread *thred)
{
	pthread_t tid = thred->id;
	char *thread_tcb, *top_sp;

	/*
	 * For HPUX DCE threads, pthread_t is a struct with the
	 * following three fields (see pthread.h, dce/cma.h):
	 *     cma_t_address       field1;
	 *     short int           field2;
	 *     short int           field3;
	 * where cma_t_address is typedef'd to be either void*
	 * or char*.
	 */
	PR_LOG(_pr_gc_lm, PR_LOG_ALWAYS, ("Begin PR_GetSP\n"));
	thread_tcb = (char*)tid.field1;
	top_sp = *(char**)(thread_tcb + 128);
	PR_LOG(_pr_gc_lm, PR_LOG_ALWAYS, ("End PR_GetSP %X \n", top_sp));
	return top_sp;
}  /* PR_GetSP */

#endif /* !defined(_PR_DCETHREADS) */

#endif  /* defined(_PR_PTHREADS) || defined(_PR_DCETHREADS) */

/* ptthread.c */