4a027d50c7
for the process, not a separate set for each thread). By default, the process now only has signal handlers installed for SIGVTALRM, SIGINFO and SIGCHLD. The thread kernel signal handler is installed for other signals on demand. This means that SIG_IGN and SIG_DFL processing is now left to the kernel, not the thread kernel. Change the signal dispatch to no longer use a signal thread, and call the signal handler using the stack of the thread that has the signal pending. Change the atomic lock method to use test-and-set asm code with a yield if blocked. This introduces separate locks for each type of object instead of blocking signals to prevent a context switch. It was this blocking of signals that caused the performance degradation the people have noted. This is a *big* change!
323 lines
8.4 KiB
C
323 lines
8.4 KiB
C
/*
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* Copyright (c) 1995-1998 John Birrell <jb@cimlogic.com.au>
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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* 3. All advertising materials mentioning features or use of this software
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* must display the following acknowledgement:
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* This product includes software developed by John Birrell.
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* 4. Neither the name of the author nor the names of any co-contributors
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* may be used to endorse or promote products derived from this software
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* without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY JOHN BIRRELL AND CONTRIBUTORS ``AS IS'' AND
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* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*
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*/
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#include <signal.h>
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#include <fcntl.h>
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#include <unistd.h>
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#include <errno.h>
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#ifdef _THREAD_SAFE
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#include <pthread.h>
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#include "pthread_private.h"
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/* Static variables: */
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static int volatile yield_on_unlock_dead = 0;
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static int volatile yield_on_unlock_thread = 0;
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static long volatile thread_dead_lock = 0;
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static long volatile thread_link_list_lock = 0;
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/* Lock the thread list: */
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void
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_lock_thread_list()
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{
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/* Lock the thread list: */
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_spinlock(&thread_link_list_lock);
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}
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/* Lock the dead thread list: */
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void
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_lock_dead_thread_list()
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{
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/* Lock the dead thread list: */
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_spinlock(&thread_dead_lock);
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}
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/* Lock the thread list: */
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void
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_unlock_thread_list()
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{
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/* Unlock the thread list: */
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_atomic_unlock(&thread_link_list_lock);
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/*
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* Check if a scheduler interrupt occurred while the thread
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* list was locked:
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*/
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if (yield_on_unlock_thread) {
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/* Reset the interrupt flag: */
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yield_on_unlock_thread = 0;
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/* This thread has overstayed it's welcome: */
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sched_yield();
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}
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}
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/* Lock the dead thread list: */
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void
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_unlock_dead_thread_list()
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{
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/* Unlock the dead thread list: */
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_atomic_unlock(&thread_dead_lock);
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/*
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* Check if a scheduler interrupt occurred while the dead
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* thread list was locked:
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*/
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if (yield_on_unlock_dead) {
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/* Reset the interrupt flag: */
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yield_on_unlock_dead = 0;
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/* This thread has overstayed it's welcome: */
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sched_yield();
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}
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}
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void
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_thread_sig_handler(int sig, int code, struct sigcontext * scp)
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{
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char c;
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int i;
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int dispatch = 0;
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pthread_t pthread;
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/*
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* Check if the pthread kernel has unblocked signals (or is about to)
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* and was on its way into a _select when the current
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* signal interrupted it:
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*/
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if (_thread_kern_in_select) {
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/* Cast the signal number to a character variable: */
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c = sig;
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/*
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* Write the signal number to the kernel pipe so that it will
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* be ready to read when this signal handler returns. This
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* means that the _select call will complete
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* immediately.
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*/
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_thread_sys_write(_thread_kern_pipe[1], &c, 1);
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}
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/* Check if the signal requires a dump of thread information: */
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if (sig == SIGINFO)
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/* Dump thread information to file: */
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_thread_dump_info();
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/* Check if an interval timer signal: */
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else if (sig == SIGVTALRM) {
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/* Check if the scheduler interrupt has come at an
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* unfortunate time which one of the threads is
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* modifying the thread list:
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*/
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if (thread_link_list_lock)
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/*
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* Set a flag so that the thread that has
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* the lock yields when it unlocks the
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* thread list:
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*/
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yield_on_unlock_thread = 1;
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/* Check if the scheduler interrupt has come at an
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* unfortunate time which one of the threads is
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* modifying the dead thread list:
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*/
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if (thread_dead_lock)
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/*
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* Set a flag so that the thread that has
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* the lock yields when it unlocks the
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* dead thread list:
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*/
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yield_on_unlock_dead = 1;
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/*
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* Check if the kernel has not been interrupted while
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* executing scheduler code:
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*/
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else if (!_thread_kern_in_sched) {
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/*
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* Schedule the next thread. This function is not
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* expected to return because it will do a longjmp
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* instead.
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*/
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_thread_kern_sched(scp);
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/*
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* This point should not be reached, so abort the
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* process:
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*/
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PANIC("Returned to signal function from scheduler");
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}
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} else {
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/* Check if a child has terminated: */
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if (sig == SIGCHLD) {
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/*
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* Go through the file list and set all files
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* to non-blocking again in case the child
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* set some of them to block. Sigh.
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*/
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for (i = 0; i < _thread_dtablesize; i++) {
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/* Check if this file is used: */
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if (_thread_fd_table[i] != NULL) {
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/*
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* Set the file descriptor to
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* non-blocking:
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*/
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_thread_sys_fcntl(i, F_SETFL,
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_thread_fd_table[i]->flags |
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O_NONBLOCK);
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}
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}
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}
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/*
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* POSIX says that pending SIGCONT signals are
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* discarded when one of there signals occurs.
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*/
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if (sig == SIGTSTP || sig == SIGTTIN || sig == SIGTTOU) {
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/*
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* Enter a loop to discard pending SIGCONT
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* signals:
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*/
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for (pthread = _thread_link_list;
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pthread != NULL;
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pthread = pthread->nxt)
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sigdelset(&pthread->sigpend,SIGCONT);
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}
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/* Check if the signal is not being ignored: */
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if (_thread_sigact[sig - 1].sa_handler != SIG_IGN)
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/*
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* Enter a loop to process each thread in the linked
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* list:
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*/
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for (pthread = _thread_link_list; pthread != NULL;
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pthread = pthread->nxt)
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_thread_signal(pthread,sig);
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/* Dispatch pending signals to the running thread: */
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_dispatch_signals();
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}
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/* Returns nothing. */
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return;
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}
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/* Perform thread specific actions in response to a signal: */
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void
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_thread_signal(pthread_t pthread, int sig)
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{
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pthread_t saved;
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struct sigaction act;
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/*
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* Flag the signal as pending. It will be dispatched later.
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*/
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sigaddset(&pthread->sigpend,sig);
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/* Check if system calls are not restarted: */
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if ((_thread_sigact[sig - 1].sa_flags & SA_RESTART) == 0) {
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/*
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* Process according to thread state:
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*/
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switch (pthread->state) {
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/*
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* States which do not change when a signal is trapped:
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*/
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case PS_COND_WAIT:
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case PS_DEAD:
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case PS_FDLR_WAIT:
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case PS_FDLW_WAIT:
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case PS_FILE_WAIT:
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case PS_JOIN:
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case PS_MUTEX_WAIT:
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case PS_RUNNING:
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case PS_STATE_MAX:
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case PS_SIGTHREAD:
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case PS_SUSPENDED:
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/* Nothing to do here. */
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break;
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/*
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* States that are interrupted by the occurrence of a signal
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* other than the scheduling alarm:
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*/
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case PS_FDR_WAIT:
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case PS_FDW_WAIT:
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case PS_SLEEP_WAIT:
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case PS_SIGWAIT:
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case PS_WAIT_WAIT:
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case PS_SELECT_WAIT:
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/* Flag the operation as interrupted: */
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pthread->interrupted = 1;
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/* Change the state of the thread to run: */
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PTHREAD_NEW_STATE(pthread,PS_RUNNING);
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/* Return the signal number: */
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pthread->signo = sig;
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break;
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}
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}
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}
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/* Dispatch pending signals to the running thread: */
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void
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_dispatch_signals()
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{
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int i;
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/*
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* Check if there are pending signals for the running
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* thread that aren't blocked:
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*/
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if ((_thread_run->sigpend & ~_thread_run->sigmask) != 0)
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/* Look for all possible pending signals: */
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for (i = 1; i < NSIG; i++)
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/*
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* Check that a custom handler is installed
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* and if the signal is not blocked:
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*/
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if (_thread_sigact[i - 1].sa_handler != SIG_DFL &&
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_thread_sigact[i - 1].sa_handler != SIG_IGN &&
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sigismember(&_thread_run->sigpend,i) &&
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!sigismember(&_thread_run->sigmask,i)) {
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/* Clear the pending signal: */
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sigdelset(&_thread_run->sigpend,i);
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/*
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* Dispatch the signal via the custom signal
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* handler:
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*/
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(*(_thread_sigact[i - 1].sa_handler))(i);
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}
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}
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#endif
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