Change signal model to match POSIX (i.e. one set of signal handlers

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!

1 files changed, 227 insertions, 72 deletions

diff --git a/lib/libpthread/thread/thr_sig.c b/lib/libpthread/thread/thr_sig.c
index e73d5a2..1e5ee63 100644
--- a/lib/libpthread/thread/thr_sig.c
+++ b/lib/libpthread/thread/thr_sig.c
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 1995 John Birrell <jb@cimlogic.com.au>.
+ * Copyright (c) 1995-1998 John Birrell <jb@cimlogic.com.au>
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
@@ -38,16 +38,79 @@
 #include <pthread.h>
 #include "pthread_private.h"
 
+/* Static variables: */
+static int	volatile yield_on_unlock_dead		= 0;
+static int	volatile yield_on_unlock_thread	= 0;
+static long	volatile thread_dead_lock		= 0;
+static long	volatile thread_link_list_lock		= 0;
+
+/* Lock the thread list: */
+void
+_lock_thread_list()
+{
+	/* Lock the thread list: */
+	_spinlock(&thread_link_list_lock);
+}
+
+/* Lock the dead thread list: */
+void
+_lock_dead_thread_list()
+{
+	/* Lock the dead thread list: */
+	_spinlock(&thread_dead_lock);
+}
+
+/* Lock the thread list: */
+void
+_unlock_thread_list()
+{
+	/* Unlock the thread list: */
+	_atomic_unlock(&thread_link_list_lock);
+
+	/*
+	 * Check if a scheduler interrupt occurred while the thread
+	 * list was locked:
+	 */
+	if (yield_on_unlock_thread) {
+		/* Reset the interrupt flag: */
+		yield_on_unlock_thread = 0;
+
+		/* This thread has overstayed it's welcome: */
+		sched_yield();
+	}
+}
+
+/* Lock the dead thread list: */
+void
+_unlock_dead_thread_list()
+{
+	/* Unlock the dead thread list: */
+	_atomic_unlock(&thread_dead_lock);
+
+	/*
+	 * Check if a scheduler interrupt occurred while the dead
+	 * thread list was locked:
+	 */
+	if (yield_on_unlock_dead) {
+		/* Reset the interrupt flag: */
+		yield_on_unlock_dead = 0;
+
+		/* This thread has overstayed it's welcome: */
+		sched_yield();
+	}
+}
+
 void
 _thread_sig_handler(int sig, int code, struct sigcontext * scp)
 {
 	char            c;
 	int             i;
+	int		dispatch = 0;
 	pthread_t       pthread;
 
 	/*
 	 * Check if the pthread kernel has unblocked signals (or is about to)
-	 * and was on its way into a _thread_sys_select when the current
+	 * and was on its way into a _select when the current
 	 * signal interrupted it: 
 	 */
 	if (_thread_kern_in_select) {
@@ -57,51 +120,65 @@ _thread_sig_handler(int sig, int code, struct sigcontext * scp)
 		/*
 		 * Write the signal number to the kernel pipe so that it will
 		 * be ready to read when this signal handler returns. This
-		 * means that the _thread_sys_select call will complete
+		 * means that the _select call will complete
 		 * immediately. 
 		 */
-		if (_thread_sys_write(_thread_kern_pipe[1], &c, 1) != 1) {
-		}
+		_thread_sys_write(_thread_kern_pipe[1], &c, 1);
 	}
+
 	/* Check if the signal requires a dump of thread information: */
-	if (sig == SIGINFO) {
+	if (sig == SIGINFO)
 		/* Dump thread information to file: */
 		_thread_dump_info();
-	} else {
-		/* Handle depending on signal type: */
-		switch (sig) {
-		/* Interval timer used for timeslicing: */
-		case SIGVTALRM:
+
+	/* Check if an interval timer signal: */
+	else if (sig == SIGVTALRM) {
+		/* Check if the scheduler interrupt has come at an
+		 * unfortunate time which one of the threads is
+		 * modifying the thread list:
+		 */
+		if (thread_link_list_lock)
 			/*
-			 * Don't add the signal to any thread.  Just want to
-			 * call the scheduler:
+			 * Set a flag so that the thread that has
+			 * the lock yields when it unlocks the
+			 * thread list:
 			 */
-			break;
+			yield_on_unlock_thread = 1;
 
-		/* Child termination: */
-		case SIGCHLD:
+		/* Check if the scheduler interrupt has come at an
+		 * unfortunate time which one of the threads is
+		 * modifying the dead thread list:
+		 */
+		if (thread_dead_lock)
 			/*
-			 * Enter a loop to process each thread in the linked
-			 * list:
+			 * Set a flag so that the thread that has
+			 * the lock yields when it unlocks the
+			 * dead thread list:
 			 */
-			for (pthread = _thread_link_list; pthread != NULL;
-			     pthread = pthread->nxt) {
-				/*
-				 * Add the signal to the set of pending
-				 * signals:
-				 */
-				pthread->sigpend[sig] += 1;
-				if (pthread->state == PS_WAIT_WAIT) {
-					/* Reset the error: */
-					/* There should be another flag so that this is not required! ### */
-					_thread_seterrno(pthread, 0);
-
-					/* Change the state of the thread to run: */
-					PTHREAD_NEW_STATE(pthread,PS_RUNNING);
-				}
-			}
+			yield_on_unlock_dead = 1;
+
+		/*
+		 * Check if the kernel has not been interrupted while
+		 * executing scheduler code:
+		 */
+		else if (!_thread_kern_in_sched) {
+			/*
+			 * Schedule the next thread. This function is not
+			 * expected to return because it will do a longjmp
+			 * instead. 
+			 */
+			_thread_kern_sched(scp);
 
 			/*
+			 * This point should not be reached, so abort the
+			 * process: 
+			 */
+			PANIC("Returned to signal function from scheduler");
+		}
+	} else {
+		/* Check if a child has terminated: */
+		if (sig == SIGCHLD) {
+			/*
 			 * Go through the file list and set all files
 			 * to non-blocking again in case the child
 			 * set some of them to block. Sigh.
@@ -109,59 +186,137 @@ _thread_sig_handler(int sig, int code, struct sigcontext * scp)
 			for (i = 0; i < _thread_dtablesize; i++) {
 				/* Check if this file is used: */
 				if (_thread_fd_table[i] != NULL) {
-					/* Set the file descriptor to non-blocking: */
-					_thread_sys_fcntl(i, F_SETFL, _thread_fd_table[i]->flags | O_NONBLOCK);
+					/*
+					 * Set the file descriptor to
+					 * non-blocking:
+					 */
+					_thread_sys_fcntl(i, F_SETFL,
+					    _thread_fd_table[i]->flags |
+					    O_NONBLOCK);
 				}
 			}
-			break;
+		}
 
-		/* Signals specific to the running thread: */
-		case SIGBUS:
-		case SIGEMT:
-		case SIGFPE:
-		case SIGILL:
-		case SIGPIPE:
-		case SIGSEGV:
-		case SIGSYS:
-			/* Add the signal to the set of pending signals: */
-			_thread_run->sigpend[sig] += 1;
-			break;
+		/*
+		 * POSIX says that pending SIGCONT signals are
+		 * discarded when one of there signals occurs.
+		 */
+		if (sig == SIGTSTP || sig == SIGTTIN || sig == SIGTTOU) {
+			/*
+			 * Enter a loop to discard pending SIGCONT
+			 * signals:
+			 */
+			for (pthread = _thread_link_list;
+			    pthread != NULL;
+			    pthread = pthread->nxt)
+				sigdelset(&pthread->sigpend,SIGCONT);
+		}
 
-		/* Signals to send to all threads: */
-		default:
+		/* Check if the signal is not being ignored: */
+		if (_thread_sigact[sig - 1].sa_handler != SIG_IGN)
 			/*
 			 * Enter a loop to process each thread in the linked
 			 * list: 
 			 */
 			for (pthread = _thread_link_list; pthread != NULL;
-			     pthread = pthread->nxt) {
-				/*
-				 * Add the signal to the set of pending
-				 * signals: 
-				 */
-				pthread->sigpend[sig] += 1;
-			}
+			     pthread = pthread->nxt)
+				_thread_signal(pthread,sig);
+
+		/* Dispatch pending signals to the running thread: */
+		_dispatch_signals();
+	}
+
+	/* Returns nothing. */
+	return;
+}
+
+/* Perform thread specific actions in response to a signal: */
+void
+_thread_signal(pthread_t pthread, int sig)
+{
+	pthread_t saved;
+	struct sigaction act;
+
+	/*
+	 * Flag the signal as pending. It will be dispatched later.
+	 */
+	sigaddset(&pthread->sigpend,sig);
+
+	/* Check if system calls are not restarted: */
+	if ((_thread_sigact[sig - 1].sa_flags & SA_RESTART) == 0) {
+		/*
+		 * Process according to thread state:
+		 */
+		switch (pthread->state) {
+		/*
+		 * States which do not change when a signal is trapped:
+		 */
+		case PS_COND_WAIT:
+		case PS_DEAD:
+		case PS_FDLR_WAIT:
+		case PS_FDLW_WAIT:
+		case PS_FILE_WAIT:
+		case PS_JOIN:
+		case PS_MUTEX_WAIT:
+		case PS_RUNNING:
+		case PS_STATE_MAX:
+		case PS_SIGTHREAD:
+		case PS_SUSPENDED:
+			/* Nothing to do here. */
+			break;
+
+		/*
+		 * States that are interrupted by the occurrence of a signal
+		 * other than the scheduling alarm: 
+		 */
+		case PS_FDR_WAIT:
+		case PS_FDW_WAIT:
+		case PS_SLEEP_WAIT:
+		case PS_SIGWAIT:
+		case PS_WAIT_WAIT:
+		case PS_SELECT_WAIT:
+			/* Flag the operation as interrupted: */
+			pthread->interrupted = 1;
+
+			/* Change the state of the thread to run: */
+			PTHREAD_NEW_STATE(pthread,PS_RUNNING);
+
+			/* Return the signal number: */
+			pthread->signo = sig;
 			break;
 		}
+	}
+}
 
-		/* Check if the kernel is not locked: */
-		if (_thread_run != &_thread_kern_thread) {
-			/*
-			 * Schedule the next thread. This function is not
-			 * expected to return because it will do a longjmp
-			 * instead. 
-			 */
-			_thread_kern_sched(scp);
+/* Dispatch pending signals to the running thread: */
+void
+_dispatch_signals()
+{
+	int i;
 
+	/*
+	 * Check if there are pending signals for the running
+	 * thread that aren't blocked:
+	 */
+	if ((_thread_run->sigpend & ~_thread_run->sigmask) != 0)
+		/* Look for all possible pending signals: */
+		for (i = 1; i < NSIG; i++)
 			/*
-			 * This point should not be reached, so abort the
-			 * process: 
+			 * Check that a custom handler is installed
+			 * and if the signal is not blocked:
 			 */
-			PANIC("Returned to signal function from scheduler");
-		}
-	}
+			if (_thread_sigact[i - 1].sa_handler != SIG_DFL &&
+			    _thread_sigact[i - 1].sa_handler != SIG_IGN &&
+			    sigismember(&_thread_run->sigpend,i) &&
+			    !sigismember(&_thread_run->sigmask,i)) {
+				/* Clear the pending signal: */
+				sigdelset(&_thread_run->sigpend,i);
 
-	/* Returns nothing. */
-	return;
+				/*
+				 * Dispatch the signal via the custom signal
+				 * handler:
+				 */
+				(*(_thread_sigact[i - 1].sa_handler))(i);
+			}
 }
 #endif