path: root/lib/libpthread/uthread/uthread_kern.c

/*	$OpenBSD: uthread_kern.c,v 1.39 2011/09/05 21:24:24 guenther Exp $	*/
/*
 * Copyright (c) 1995-1998 John Birrell <jb@cimlogic.com.au>
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *	This product includes software developed by John Birrell.
 * 4. Neither the name of the author nor the names of any co-contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY JOHN BIRRELL AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 * $FreeBSD: uthread_kern.c,v 1.23 1999/09/29 15:18:39 marcel Exp $
 *
 */
#include <errno.h>
#include <poll.h>
#include <stdlib.h>
#include <stdarg.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/time.h>
#include <sys/socket.h>
#include <sys/uio.h>
#include <sys/syscall.h>
#include <fcntl.h>
#ifdef _THREAD_SAFE
#include <pthread.h>
#include "pthread_private.h"

/*
 * local functions.   Do NOT make these static... we want so see them in
 * crash dumps.
 */
void		_thread_kern_poll(int);
void		_dequeue_signals(void);
inline void	_thread_run_switch_hook(pthread_t, pthread_t);

/* Static variables: */
static unsigned int	last_tick = 0;

void
_thread_kern_sched(struct sigcontext * scp)
{
	struct timespec	ts;
	struct timeval	tv;
	struct pthread	*curthread = _get_curthread();
	pthread_t       pthread, pthread_h;
	unsigned int	current_tick;
	int		add_to_prioq;
	pthread_t	old_thread_run;

	/*
	 * Flag the pthread kernel as executing scheduler code
	 * to avoid a scheduler signal from interrupting this
	 * execution and calling the scheduler again.
	 */
	_thread_kern_in_sched = 1;

	/* Check if this function was called from the signal handler: */
	if (scp != NULL) {
		/*
		 * The signal handler should have saved the state of
		 * the current thread. Restore the process signal
		 * mask.
		 */
		if (_thread_sys_sigprocmask(SIG_SETMASK,
		    &_process_sigmask, NULL) != 0)
			PANIC("Unable to restore process mask after signal");

		/*
		 * Copy the signal context to the current thread's jump
		 * buffer:
		 */
		memcpy(&curthread->saved_sigcontext, scp,
		    sizeof(curthread->saved_sigcontext));

		/* Flag the signal context as the last state saved: */
		curthread->sig_saved = 1;
	} else
		/* Flag the jump buffer was the last state saved: */
		curthread->sig_saved = 0;

	/* If the currently running thread is a user thread, save it: */
	if ((curthread->flags & PTHREAD_FLAGS_PRIVATE) == 0)
		_last_user_thread = curthread;

	/* Save floating point state. */
	_thread_machdep_save_float_state(&curthread->_machdep);

	/* Save errno. */
	curthread->error = errno;

	/* Save the current thread to switch from */
	old_thread_run = curthread;

	/*
	 * Enter a scheduling loop that finds the next thread that is
	 * ready to run. This loop completes when there are no more threads
	 * in the global list or when a thread has its state restored by
	 * either a sigreturn (if the state was saved as a sigcontext) or a
	 * switch.
	 */
	while (!(TAILQ_EMPTY(&_thread_list))) {
		/* Get the current time of day: */
		GET_CURRENT_TOD(tv);
		TIMEVAL_TO_TIMESPEC(&tv, &ts);
		current_tick = _sched_ticks;

		/*
		 * Protect the scheduling queues from access by the signal
		 * handler.
		 */
		_queue_signals = 1;
		add_to_prioq = 0;

		if (curthread != &_thread_kern_thread) {
			/*
			 * This thread no longer needs to yield the CPU.
			 */
			curthread->yield_on_sig_undefer = 0;
	
			if (curthread->state != PS_RUNNING) {
				/*
				 * Save the current time as the time that the
				 * thread became inactive:
				 */
				curthread->last_inactive = (long)current_tick;
				if (curthread->last_inactive <
				    curthread->last_active) {
					/* Account for a rollover: */
					curthread->last_inactive =+
					    UINT_MAX + 1;
				}
			}

			/*
			 * Place the currently running thread into the
			 * appropriate queue(s).
			 */
			switch (curthread->state) {
			case PS_DEAD:
			case PS_STATE_MAX: /* to silence -Wall */
			case PS_SUSPENDED:
				/*
				 * Dead and suspended threads are not placed
				 * in any queue:
				 */
				break;

			case PS_RUNNING:
				/*
				 * Runnable threads can't be placed in the
				 * priority queue until after waiting threads
				 * are polled (to preserve round-robin
				 * scheduling).
				 */
				add_to_prioq = 1;
				break;

			/*
			 * States which do not depend on file descriptor I/O
			 * operations or timeouts:
			 */
			case PS_DEADLOCK:
			case PS_FDLR_WAIT:
			case PS_FDLW_WAIT:
			case PS_FILE_WAIT:
			case PS_JOIN:
			case PS_MUTEX_WAIT:
			case PS_SIGSUSPEND:
			case PS_SIGTHREAD:
			case PS_SIGWAIT:
			case PS_WAIT_WAIT:
				/* No timeouts for these states: */
				curthread->wakeup_time.tv_sec = -1;
				curthread->wakeup_time.tv_nsec = -1;

				/* Restart the time slice: */
				curthread->slice_usec = -1;

				/* Insert into the waiting queue: */
				PTHREAD_WAITQ_INSERT(curthread);
				break;

			/* States which can timeout: */
			case PS_COND_WAIT:
			case PS_SLEEP_WAIT:
				/* Restart the time slice: */
				curthread->slice_usec = -1;

				/* Insert into the waiting queue: */
				PTHREAD_WAITQ_INSERT(curthread);
				break;
	
			/* States that require periodic work: */
			case PS_SPINBLOCK:
				/* No timeouts for this state: */
				curthread->wakeup_time.tv_sec = -1;
				curthread->wakeup_time.tv_nsec = -1;

				/* Increment spinblock count: */
				_spinblock_count++;

				/* FALLTHROUGH */
			case PS_FDR_WAIT:
			case PS_FDW_WAIT:
			case PS_POLL_WAIT:
			case PS_SELECT_WAIT:
				/* Restart the time slice: */
				curthread->slice_usec = -1;
	
				/* Insert into the waiting queue: */
				PTHREAD_WAITQ_INSERT(curthread);
	
				/* Insert into the work queue: */
				PTHREAD_WORKQ_INSERT(curthread);
				break;
			}
		}

		/*
		 * Avoid polling file descriptors if there are none
		 * waiting:
		 */
		if (TAILQ_EMPTY(&_workq) != 0) {
		}
		/*
		 * Poll file descriptors only if a new scheduling signal
		 * has occurred or if we have no more runnable threads.
		 */
		else if (((current_tick = _sched_ticks) != last_tick) ||
		    ((curthread->state != PS_RUNNING) &&
		    (PTHREAD_PRIOQ_FIRST() == NULL))) {
			/* Unprotect the scheduling queues: */
			_queue_signals = 0;

			/*
			 * Poll file descriptors to update the state of threads
			 * waiting on file I/O where data may be available:
			 */
			_thread_kern_poll(0);

			/* Protect the scheduling queues: */
			_queue_signals = 1;
		}
		last_tick = current_tick;

		/*
		 * Wake up threads that have timedout.  This has to be
		 * done after polling in case a thread does a poll or
		 * select with zero time.
		 */
		PTHREAD_WAITQ_SETACTIVE();
		while (((pthread = TAILQ_FIRST(&_waitingq)) != NULL) &&
		       (pthread->wakeup_time.tv_sec != -1) &&
		       (((pthread->wakeup_time.tv_sec == 0) &&
			 (pthread->wakeup_time.tv_nsec == 0)) ||
			(pthread->wakeup_time.tv_sec < ts.tv_sec) ||
			((pthread->wakeup_time.tv_sec == ts.tv_sec) &&
			 (pthread->wakeup_time.tv_nsec <= ts.tv_nsec)))) {
			switch (pthread->state) {
			case PS_POLL_WAIT:
			case PS_SELECT_WAIT:
				/* Return zero file descriptors ready: */
				pthread->data.poll_data->nfds = 0;
				/* fall through */
			default:
				/*
				 * Remove this thread from the waiting queue
				 * (and work queue if necessary) and place it
				 * in the ready queue.
				 */
				PTHREAD_WAITQ_CLEARACTIVE();
				if (pthread->flags & PTHREAD_FLAGS_IN_WORKQ)
					PTHREAD_WORKQ_REMOVE(pthread);
				PTHREAD_NEW_STATE(pthread, PS_RUNNING);
				PTHREAD_WAITQ_SETACTIVE();
				break;
			}
			/*
			 * Flag the timeout in the thread structure:
			 */
			pthread->timeout = 1;
		}
		PTHREAD_WAITQ_CLEARACTIVE();

		/*
		 * Check to see if the current thread needs to be added
		 * to the priority queue:
		 */
		if (add_to_prioq != 0) {
			/*
			 * Save the current time as the time that the
			 * thread became inactive:
			 */
			current_tick = _sched_ticks;
			curthread->last_inactive = (long)current_tick;
			if (curthread->last_inactive <
			    curthread->last_active) {
				/* Account for a rollover: */
				curthread->last_inactive =+ UINT_MAX + 1;
			}

			if ((curthread->slice_usec != -1) &&
			   (curthread->attr.sched_policy != SCHED_FIFO)) {
				/*
				 * Accumulate the number of microseconds for
				 * which the current thread has run:
				 */
				curthread->slice_usec +=
				    (curthread->last_inactive -
				    curthread->last_active) *
				    (long)_clock_res_usec;
				/* Check for time quantum exceeded: */
				if (curthread->slice_usec > TIMESLICE_USEC)
					curthread->slice_usec = -1;
			}

			if (curthread->slice_usec == -1) {
				/*
				 * The thread exceeded its time
				 * quantum or it yielded the CPU;
				 * place it at the tail of the
				 * queue for its priority.
				 */
				PTHREAD_PRIOQ_INSERT_TAIL(curthread);
			} else {
				/*
				 * The thread hasn't exceeded its
				 * interval.  Place it at the head
				 * of the queue for its priority.
				 */
				PTHREAD_PRIOQ_INSERT_HEAD(curthread);
			}
		}

		/*
		 * Get the highest priority thread in the ready queue.
		 */
		pthread_h = PTHREAD_PRIOQ_FIRST();

		/* Check if there are no threads ready to run: */
		if (pthread_h == NULL) {
			/*
			 * Lock the pthread kernel by changing the pointer to
			 * the running thread to point to the global kernel
			 * thread structure:
			 */
			_set_curthread(&_thread_kern_thread);
			curthread = &_thread_kern_thread;

			/* Unprotect the scheduling queues: */
			_queue_signals = 0;

			/*
			 * There are no threads ready to run, so wait until
			 * something happens that changes this condition:
			 */
			_thread_kern_poll(1);

			/*
			 * This process' usage will likely be very small
			 * while waiting in a poll.  Since the scheduling
			 * clock is based on the profiling timer, it is
			 * unlikely that the profiling timer will fire
			 * and update the time of day.  To account for this,
			 * get the time of day after polling with a timeout.
			 */
			gettimeofday((struct timeval *) &_sched_tod, NULL);

			/* Check once more for a runnable thread: */
			_queue_signals = 1;
			pthread_h = PTHREAD_PRIOQ_FIRST();
			_queue_signals = 0;
		}

		if (pthread_h != NULL) {
			/* Remove the thread from the ready queue: */
			PTHREAD_PRIOQ_REMOVE(pthread_h);

			/* Unprotect the scheduling queues: */
			_queue_signals = 0;

			/*
			 * Check for signals queued while the scheduling
			 * queues were protected:
			 */
			while (_sigq_check_reqd != 0) {
				/* Clear before handling queued signals: */
				_sigq_check_reqd = 0;

				/* Protect the scheduling queues again: */
				_queue_signals = 1;

				_dequeue_signals();

				/*
				 * Check for a higher priority thread that
				 * became runnable due to signal handling.
				 */
				if (((pthread = PTHREAD_PRIOQ_FIRST()) != NULL) &&
				    (pthread->active_priority > pthread_h->active_priority)) {
					/* Remove the thread from the ready queue: */
					PTHREAD_PRIOQ_REMOVE(pthread);

					/*
					 * Insert the lower priority thread
					 * at the head of its priority list:
					 */
					PTHREAD_PRIOQ_INSERT_HEAD(pthread_h);

					/* There's a new thread in town: */
					pthread_h = pthread;
				}

				/* Unprotect the scheduling queues: */
				_queue_signals = 0;
			}

			/*
			 * Prevent the signal handler from fiddling with this
			 * thread before its state is set.
			 */
			_queue_signals = 1;

			/* Make the selected thread the current thread: */
			_set_curthread(pthread_h);
			curthread = pthread_h;

			/*
			 * Save the current time as the time that the thread
			 * became active:
			 */
			current_tick = _sched_ticks;
			curthread->last_active = (long) current_tick;

			/*
			 * Check if this thread is running for the first time
			 * or running again after using its full time slice
			 * allocation:
			 */
			if (curthread->slice_usec == -1) {
				/* Reset the accumulated time slice period: */
				curthread->slice_usec = 0;
			}

			/* Restore errno. */
			errno = curthread->error;

			/*
			 * If we're 'switching' to the current thread,
			 * then don't bother with the save/restore
			 */
			if (curthread == old_thread_run)
				goto after_switch;

			/* Restore floating point state. */
			_thread_machdep_restore_float_state(&curthread->_machdep);

			/* Restore the new thread, saving current. */
			_thread_machdep_switch(&curthread->_machdep,
					       &old_thread_run->_machdep);

			/*
			 * DANGER WILL ROBINSON
			 * All stack local variables now contain the values
			 * they had when this thread was last running.  In
			 * particular, curthread is NOT pointing to the
			 * current thread.   Make it point to the current
			 * before use.
			 */
			curthread = _get_curthread();

		  after_switch:

			/* Allow signals again. */
			_queue_signals = 0;

			/* Done with scheduling. */
			_thread_kern_in_sched = 0;

			/* run any installed switch-hooks */
			if ((_sched_switch_hook != NULL) &&
			    (_last_user_thread != curthread)) {
				_thread_run_switch_hook(_last_user_thread,
							curthread);
			}

			/* check for thread cancellation */
			if (((curthread->cancelflags &
			      PTHREAD_AT_CANCEL_POINT) == 0) &&
			    ((curthread->cancelflags &
			      PTHREAD_CANCEL_ASYNCHRONOUS) != 0))
				pthread_testcancel();

			/* dispatch any pending signals if possible */
			if (curthread->sig_defer_count == 0)
				_dispatch_signals(scp);

			/* Check if a signal context was saved: */
			if (curthread->sig_saved == 1) {
				/* return to signal handler.   This code
				   should be:
				   _thread_sys_sigreturn(&curthread->saved_sigcontext);
				   but that doesn't currently work on the
				   sparc */
				return;
			} else {
				/* This is the normal way out */
				return;
			}

			/* This point should not be reached. */
			PANIC("Thread has returned from sigreturn or switch");
		}
	}

	/* There are no more threads, so exit this process: */
	exit(0);
}

void
_thread_kern_sched_state(enum pthread_state state, const char *fname,
			 int lineno)
{
	struct pthread	*curthread = _get_curthread();

	/*
	 * Flag the pthread kernel as executing scheduler code
	 * to avoid a scheduler signal from interrupting this
	 * execution and calling the scheduler again.
	 */
	_thread_kern_in_sched = 1;

	/*
	 * Prevent the signal handler from fiddling with this thread
	 * before its state is set and is placed into the proper queue.
	 */
	_queue_signals = 1;

	/* Change the state of the current thread: */
	curthread->state = state;
	curthread->fname = fname;
	curthread->lineno = lineno;

	/* Schedule the next thread that is ready: */
	_thread_kern_sched(NULL);
}

void
_thread_kern_sched_state_unlock(enum pthread_state state, spinlock_t *lock,
				const char *fname, int lineno)
{
	struct pthread	*curthread = _get_curthread();

	/*
	 * Flag the pthread kernel as executing scheduler code
	 * to avoid a scheduler signal from interrupting this
	 * execution and calling the scheduler again.
	 */
	_thread_kern_in_sched = 1;

	/*
	 * Prevent the signal handler from fiddling with this thread
	 * before its state is set and it is placed into the proper
	 * queue(s).
	 */
	_queue_signals = 1;

	/* Change the state of the current thread: */
	curthread->state = state;
	curthread->fname = fname;
	curthread->lineno = lineno;

	_SPINUNLOCK(lock);

	/* Schedule the next thread that is ready: */
	_thread_kern_sched(NULL);
}

void
_thread_kern_poll(int wait_reqd)
{
	int             count = 0;
	int		kern_pipe_added = 0;
	nfds_t		i, found, nfds = 0;
	int		timeout_ms = 0;
	struct pthread	*pthread, *next;
	struct timespec ts;
	struct timeval  tv;

	/* Check if the caller wants to wait: */
	if (wait_reqd == 0) {
		timeout_ms = 0;
	}
	else {
		/* Get the current time of day: */
		GET_CURRENT_TOD(tv);
		TIMEVAL_TO_TIMESPEC(&tv, &ts);

		_queue_signals = 1;
		pthread = TAILQ_FIRST(&_waitingq);
		_queue_signals = 0;

		if ((pthread == NULL) || (pthread->wakeup_time.tv_sec == -1)) {
			/*
			 * Either there are no threads in the waiting queue,
			 * or there are no threads that can timeout.
			 */
			timeout_ms = INFTIM;
		}
		else if (pthread->wakeup_time.tv_sec - ts.tv_sec > 60000)
			/* Limit maximum timeout to prevent rollover. */
			timeout_ms = 60000;
		else {
			/*
			 * Calculate the time left for the next thread to
			 * timeout:
			 */
			timeout_ms = ((pthread->wakeup_time.tv_sec - ts.tv_sec) *
			    1000) + (time_t)((pthread->wakeup_time.tv_nsec - ts.tv_nsec) /
			    1000000);
			/*
			 * Don't allow negative timeouts:
			 */
			if (timeout_ms < 0)
				timeout_ms = 0;
		}
	}
			
	/* Protect the scheduling queues: */
	_queue_signals = 1;

	/*
	 * Check to see if the signal queue needs to be walked to look
	 * for threads awoken by a signal while in the scheduler.
	 */
	if (_sigq_check_reqd != 0) {
		/* Reset flag before handling queued signals: */
		_sigq_check_reqd = 0;
		_dequeue_signals();
	}

	/*
	 * Check for a thread that became runnable due to a signal:
	 */
	if (PTHREAD_PRIOQ_FIRST() != NULL) {
		/*
		 * Since there is at least one runnable thread,
		 * disable the wait.
		 */
		timeout_ms = 0;
	}

	/*
	 * Form the poll table:
	 */
	nfds = 0;
	if (timeout_ms != 0) {
		/* Add the kernel pipe to the poll table: */
		_thread_pfd_table[nfds].fd = _thread_kern_pipe[0];
		_thread_pfd_table[nfds].events = POLLRDNORM;
		_thread_pfd_table[nfds].revents = 0;
		nfds++;
		kern_pipe_added = 1;
	}

	PTHREAD_WAITQ_SETACTIVE();
	for (pthread = TAILQ_FIRST(&_workq); pthread != NULL; pthread = next) {
		next = TAILQ_NEXT(pthread, qe);
		switch (pthread->state) {
		case PS_SPINBLOCK:
			/*
			 * If the lock is available, let the thread run.
			 */
			if (pthread->data.spinlock->access_lock ==
			    _SPINLOCK_UNLOCKED) {
				PTHREAD_WAITQ_CLEARACTIVE();
				PTHREAD_WORKQ_REMOVE(pthread);
				PTHREAD_NEW_STATE(pthread,PS_RUNNING);
				PTHREAD_WAITQ_SETACTIVE();
				/* One less thread in a spinblock state: */
				_spinblock_count--;
				/*
				 * Since there is at least one runnable
				 * thread, disable the wait.
				 */
				timeout_ms = 0;
			}
			break;

		/* File descriptor read wait: */
		case PS_FDR_WAIT:
			/* if fd is closing then reschedule this thread */
			if (_thread_fd_table[pthread->data.fd.fd]->state == FD_ENTRY_CLOSING) {
				pthread->closing_fd = 1;
				PTHREAD_WAITQ_CLEARACTIVE();
				PTHREAD_WORKQ_REMOVE(pthread);
				PTHREAD_NEW_STATE(pthread,PS_RUNNING);
				PTHREAD_WAITQ_SETACTIVE();
			} else {
				/* Limit number of polled files to table size: */
				if (nfds < _thread_max_pfdtsize) {
					_thread_pfd_table[nfds].events = POLLRDNORM;
					_thread_pfd_table[nfds].fd = pthread->data.fd.fd;
					nfds++;
				}
			}
			break;

		/* File descriptor write wait: */
		case PS_FDW_WAIT:
			/* if fd is closing then reschedule this thread */
			if (_thread_fd_table[pthread->data.fd.fd]->state == FD_ENTRY_CLOSING) {
				pthread->closing_fd = 1;
				PTHREAD_WAITQ_CLEARACTIVE();
				PTHREAD_WORKQ_REMOVE(pthread);
				PTHREAD_NEW_STATE(pthread,PS_RUNNING);
				PTHREAD_WAITQ_SETACTIVE();
			} else {
				/* Limit number of polled files to table size: */
				if (nfds < _thread_max_pfdtsize) {
					_thread_pfd_table[nfds].events = POLLWRNORM;
					_thread_pfd_table[nfds].fd = pthread->data.fd.fd;
					nfds++;
				}
			}
			break;

		/* File descriptor poll or select wait: */
		case PS_POLL_WAIT:
		case PS_SELECT_WAIT:
			/* Limit number of polled files to table size: */
			if (pthread->data.poll_data->nfds + nfds <
			    _thread_max_pfdtsize) {
				for (i = 0; i < pthread->data.poll_data->nfds; i++) {
					_thread_pfd_table[nfds + i].fd =
					    pthread->data.poll_data->fds[i].fd;
					_thread_pfd_table[nfds + i].events =
					    pthread->data.poll_data->fds[i].events;
				}
				nfds += pthread->data.poll_data->nfds;
			}
			break;

		/* Other states do not depend on file I/O. */
		default:
			break;
		}
	}
	PTHREAD_WAITQ_CLEARACTIVE();

	/*
	 * Wait for a file descriptor to be ready for read, write, or
	 * an exception, or a timeout to occur:
	 */
	count = _thread_sys_poll(_thread_pfd_table, nfds, timeout_ms);

	if (kern_pipe_added != 0)
		/*
		 * Remove the pthread kernel pipe file descriptor
		 * from the pollfd table:
		 */
		nfds = 1;
	else
		nfds = 0;

	/*
	 * Check if it is possible that there are bytes in the kernel
	 * read pipe waiting to be read:
	 */
	if (count < 0 || ((kern_pipe_added != 0) &&
	    (_thread_pfd_table[0].revents & POLLRDNORM))) {
		/*
		 * If the kernel read pipe was included in the
		 * count:
		 */
		if (count > 0) {
			/* Decrement the count of file descriptors: */
			count--;
		}

		if (_sigq_check_reqd != 0) {
			/* Reset flag before handling signals: */
			_sigq_check_reqd = 0;
			_dequeue_signals();
		}
	}

	/*
	 * Check if any file descriptors are ready:
	 */
	if (count > 0) {
		/*
		 * Enter a loop to look for threads waiting on file
		 * descriptors that are flagged as available by the
		 * _poll syscall:
		 */
		PTHREAD_WAITQ_SETACTIVE();
		for (pthread = TAILQ_FIRST(&_workq); pthread != NULL;
		    pthread = next) {
			next = TAILQ_NEXT(pthread, qe);
			switch (pthread->state) {
			case PS_SPINBLOCK:
				/*
				 * If the lock is available, let the thread run.
				 */
				if (pthread->data.spinlock->access_lock ==
				    _SPINLOCK_UNLOCKED) {
					PTHREAD_WAITQ_CLEARACTIVE();
					PTHREAD_WORKQ_REMOVE(pthread);
					PTHREAD_NEW_STATE(pthread,PS_RUNNING);
					PTHREAD_WAITQ_SETACTIVE();

					/*
					 * One less thread in a spinblock state:
					 */
					_spinblock_count--;
				}
				break;

			/* File descriptor read wait: */
			case PS_FDR_WAIT:
				if ((nfds < _thread_max_pfdtsize) &&
				    (_thread_pfd_table[nfds].revents
				       & (POLLRDNORM|POLLERR|POLLHUP|POLLNVAL))
				      != 0) {
					PTHREAD_WAITQ_CLEARACTIVE();
					PTHREAD_WORKQ_REMOVE(pthread);
					PTHREAD_NEW_STATE(pthread,PS_RUNNING);
					PTHREAD_WAITQ_SETACTIVE();
				}
				nfds++;
				break;

			/* File descriptor write wait: */
			case PS_FDW_WAIT:
				if ((nfds < _thread_max_pfdtsize) &&
				    (_thread_pfd_table[nfds].revents
				       & (POLLWRNORM|POLLERR|POLLHUP|POLLNVAL))
				      != 0) {
					PTHREAD_WAITQ_CLEARACTIVE();
					PTHREAD_WORKQ_REMOVE(pthread);
					PTHREAD_NEW_STATE(pthread,PS_RUNNING);
					PTHREAD_WAITQ_SETACTIVE();
				}
				nfds++;
				break;

			/* File descriptor poll or select wait: */
			case PS_POLL_WAIT:
			case PS_SELECT_WAIT:
				if (pthread->data.poll_data->nfds + nfds <
				    _thread_max_pfdtsize) {
					/*
					 * Enter a loop looking for I/O
					 * readiness:
					 */
					found = 0;
					for (i = 0; i < pthread->data.poll_data->nfds; i++) {
						if (_thread_pfd_table[nfds + i].revents != 0) {
							pthread->data.poll_data->fds[i].revents =
							    _thread_pfd_table[nfds + i].revents;
							found++;
						}
					}

					/* Increment before destroying: */
					nfds += pthread->data.poll_data->nfds;

					if (found != 0) {
						pthread->data.poll_data->nfds = found;
						PTHREAD_WAITQ_CLEARACTIVE();
						PTHREAD_WORKQ_REMOVE(pthread);
						PTHREAD_NEW_STATE(pthread,PS_RUNNING);
						PTHREAD_WAITQ_SETACTIVE();
					}
				}
				else
					nfds += pthread->data.poll_data->nfds;
				break;

			/* Other states do not depend on file I/O. */
			default:
				break;
			}
		}
		PTHREAD_WAITQ_CLEARACTIVE();
	}
	else if (_spinblock_count != 0) {
		/*
		 * Enter a loop to look for threads waiting on a spinlock
		 * that is now available.
		 */
		PTHREAD_WAITQ_SETACTIVE();
		for (pthread = TAILQ_FIRST(&_workq); pthread != NULL;
		    pthread = next) {
			next = TAILQ_NEXT(pthread, qe);
			if (pthread->state == PS_SPINBLOCK) {
				/*
				 * If the lock is available, let the thread run.
				 */
				if (pthread->data.spinlock->access_lock ==
				    _SPINLOCK_UNLOCKED) {
					PTHREAD_WAITQ_CLEARACTIVE();
					PTHREAD_WORKQ_REMOVE(pthread);
					PTHREAD_NEW_STATE(pthread,PS_RUNNING);
					PTHREAD_WAITQ_SETACTIVE();

					/*
					 * One less thread in a spinblock state:
					 */
					_spinblock_count--;
				}
			}
		}
		PTHREAD_WAITQ_CLEARACTIVE();
	}

	/* Unprotect the scheduling queues: */
	_queue_signals = 0;

	while (_sigq_check_reqd != 0) {
		/* Handle queued signals: */
		_sigq_check_reqd = 0;

		/* Protect the scheduling queues: */
		_queue_signals = 1;
		_dequeue_signals();
		_queue_signals = 0;
	}
}

void
_thread_kern_set_timeout(const struct timespec * timeout)
{
	struct pthread	*curthread = _get_curthread();
	struct timespec current_time;
	struct timeval  tv;

	/* Reset the timeout flag for the running thread: */
	curthread->timeout = 0;

	/* Check if the thread is to wait forever: */
	if (timeout == NULL) {
		/*
		 * Set the wakeup time to something that can be recognised as
		 * different to an actual time of day:
		 */
		curthread->wakeup_time.tv_sec = -1;
		curthread->wakeup_time.tv_nsec = -1;
	}
	/* Check if no waiting is required: */
	else if (timeout->tv_sec == 0 && timeout->tv_nsec == 0) {
		/* Set the wake up time to 'immediately': */
		curthread->wakeup_time.tv_sec = 0;
		curthread->wakeup_time.tv_nsec = 0;
	} else {
		gettimeofday((struct timeval *) &_sched_tod, NULL);
		GET_CURRENT_TOD(tv);
		TIMEVAL_TO_TIMESPEC(&tv, &current_time);
		timespecadd(&current_time, timeout, &curthread->wakeup_time);
	}
}

/*
 * Function registered with dlctl to lock/unlock the kernel for
 * threade safe dlopen calls.
 *	which == 0:	defer signals (stops scheduler)
 *	which != 0:	undefer signals and process any queued sigs
 */
void
_thread_kern_lock(int which)
{
	if (which == 0)
		_thread_kern_sig_defer();
	else
		_thread_kern_sig_undefer();
}


void
_thread_kern_sig_defer(void)
{
	struct pthread	*curthread = _get_curthread();

	/* Allow signal deferral to be recursive. */
	curthread->sig_defer_count++;
}

void
_thread_kern_sig_undefer(void)
{
	struct pthread	*curthread = _get_curthread();

	/*
	 * Perform checks to yield only if we are about to undefer
	 * signals.
	 */
	if (curthread->sig_defer_count > 1) {
		/* Decrement the signal deferral count. */
		curthread->sig_defer_count--;
	}
	else if (curthread->sig_defer_count == 1) {
		/* Reenable signals: */
		curthread->sig_defer_count = 0;

		/*
		 * Check if there are queued signals:
		 */
		if (_sigq_check_reqd != 0)
			_thread_kern_sched(NULL);

		/*
		 * Check for asynchronous cancellation before delivering any
		 * pending signals:
		 */
		if (((curthread->cancelflags & PTHREAD_AT_CANCEL_POINT) == 0) &&
		    ((curthread->cancelflags & PTHREAD_CANCEL_ASYNCHRONOUS) != 0))
			pthread_testcancel();

		/*
		 * If there are pending signals or this thread has
		 * to yield the CPU, call the kernel scheduler:
		 *
		 * XXX - Come back and revisit the pending signal problem
		 */
		if ((curthread->yield_on_sig_undefer != 0) ||
		    curthread->sigpend != 0) {
			curthread->yield_on_sig_undefer = 0;
			_thread_kern_sched(NULL);
		}
	}
}

void
_dequeue_signals(void)
{
	char	bufr[128];
	int	i;
	ssize_t num;

	/*
	 * Enter a loop to read and handle queued signals from the
	 * pthread kernel pipe:
	 */
	while (((num = _thread_sys_read(_thread_kern_pipe[0], bufr,
	    sizeof(bufr))) > 0) || (num == -1 && errno == EINTR)) {
		/*
		 * The buffer read contains one byte per signal and
		 * each byte is the signal number.
		 */
		for (i = 0; i < num; i++) {
			if ((int) bufr[i] != _SCHED_SIGNAL)
				_thread_sig_handle((int) bufr[i], NULL);
		}
	}
	if ((num < 0) && (errno != EAGAIN)) {
		/*
		 * The only error we should expect is if there is
		 * no data to read.
		 */
		PANIC("Unable to read from thread kernel pipe");
	}
}

inline void
_thread_run_switch_hook(pthread_t thread_out, pthread_t thread_in)
{
	pthread_t tid_out = thread_out;
	pthread_t tid_in = thread_in;

	if ((tid_out != NULL) &&
	    (tid_out->flags & PTHREAD_FLAGS_PRIVATE) != 0)
		tid_out = NULL;
	if ((tid_in != NULL) &&
	    (tid_in->flags & PTHREAD_FLAGS_PRIVATE) != 0)
		tid_in = NULL;

	if ((_sched_switch_hook != NULL) && (tid_out != tid_in)) {
		/* Run the scheduler switch hook: */
		_sched_switch_hook(tid_out, tid_in);
	}
}

struct pthread *
_get_curthread(void)
{
	if (_thread_initial == NULL)
		_thread_init();

	return (_thread_run);
}

void
_set_curthread(struct pthread *newthread)
{
	_thread_run = newthread;
}
#endif