[ The author's description... ]

  o Runnable threads are now maintained in priority queues.  The
    implementation requires two things:

      1.) The priority queues must be protected during insertion
          and removal of threads.  Since the kernel scheduler
          must modify the priority queues, a spinlock for
          protection cannot be used.   The functions
          _thread_kern_sched_defer() and _thread_kern_sched_undefer()
          were added to {un}defer kernel scheduler activation.

      2.) A thread (active) priority change can be performed only
          when the thread is removed from the priority queue.  The
          implementation uses a threads active priority when
          inserting it into the queue.

    A by-product is that thread switches are much faster.  A
    separate queue is used for waiting and/or blocked threads,
    and it is searched at most 2 times in the kernel scheduler
    when there are active threads.  It should be possible to
    reduce this to once by combining polling of threads waiting
    on I/O with the loop that looks for timed out threads and
    the minimum timeout value.

  o Functions to defer kernel scheduler activation were added.  These
    are _thread_kern_sched_defer() and _thread_kern_sched_undefer()
    and may be called recursively.  These routines do not block the
    scheduling signal, but latch its occurrence.  The signal handler
    will not call the kernel scheduler when the running thread has
    deferred scheduling, but it will be called when running thread
    undefers scheduling.

  o Added support for _POSIX_THREAD_PRIORITY_SCHEDULING.  All the
    POSIX routines required by this should now be implemented.
    One note, SCHED_OTHER, SCHED_FIFO, and SCHED_RR are required
    to be defined by including pthread.h.  These defines are currently
    in sched.h.  I modified pthread.h to include sched.h but don't
    know if this is the proper thing to do.

  o Added support for priority protection and inheritence mutexes.
    This allows definition of _POSIX_THREAD_PRIO_PROTECT and
    _POSIX_THREAD_PRIO_INHERIT.

  o Added additional error checks required by POSIX for mutexes and
    condition variables.

  o Provided a wrapper for sigpending which is marked as a hidden
    syscall.

  o Added a non-portable function as a debugging aid to allow an
    application to monitor thread context switches.  An application
    can install a routine that gets called everytime a thread
    (explicitly created by the application) gets context switched.
    The routine gets passed the pthread IDs of the threads that are
    being switched in and out.

Submitted by: Dan Eischen <eischen@vigrid.com>

Changes by me:

  o Added a PS_SPINBLOCK state to deal with the priority inversion
    problem most often (I think) seen by threads calling malloc/free/realloc.

  o Dispatch signals to the running thread directly rather than at a
    context switch to avoid the situation where the switch never occurs.

1 files changed, 113 insertions, 0 deletions

diff --git a/lib/libpthread/thread/thr_setschedparam.c b/lib/libpthread/thread/thr_setschedparam.c
new file mode 100644
index 0000000..93635da
--- /dev/null
+++ b/lib/libpthread/thread/thr_setschedparam.c
@@ -0,0 +1,113 @@
+/*
+ * Copyright (c) 1998 Daniel Eischen <eischen@vigrid.com>.
+ * 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 Daniel Eischen.
+ * 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 DANIEL EISCHEN 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.
+ *
+ */
+#include <errno.h>
+#include <sys/param.h>
+#ifdef _THREAD_SAFE
+#include <pthread.h>
+#include "pthread_private.h"
+
+int
+pthread_setschedparam(pthread_t pthread, int policy, struct sched_param *param)
+{
+	int old_prio, in_readyq = 0, ret = 0;
+
+	if ((param == NULL) || (param->sched_priority < PTHREAD_MIN_PRIORITY) ||
+	    (param->sched_priority > PTHREAD_MAX_PRIORITY) ||
+	    (policy < SCHED_FIFO) || (policy > SCHED_RR))
+		/* Return an invalid argument error: */
+		ret = EINVAL;
+
+	/* Find the thread in the list of active threads: */
+	else if ((ret = _find_thread(pthread)) == 0) {
+		/*
+		 * Guard against being preempted by a scheduling
+		 * signal:
+		 */
+		_thread_kern_sched_defer();
+
+		if (param->sched_priority != pthread->base_priority) {
+			/*
+			 * Remove the thread from its current priority
+			 * queue before any adjustments are made to its
+			 * active priority:
+			 */
+			if ((pthread != _thread_run) &&
+			   (pthread->state == PS_RUNNING)) {
+				in_readyq = 1;
+				old_prio = pthread->active_priority;
+				PTHREAD_PRIOQ_REMOVE(pthread);
+			}
+
+			/* Set the thread base priority: */
+			pthread->base_priority = param->sched_priority;
+
+			/* Recalculate the active priority: */
+			pthread->active_priority = MAX(pthread->base_priority,
+			    pthread->inherited_priority);
+
+			if (in_readyq) {
+				if ((pthread->priority_mutex_count > 0) &&
+				    (old_prio > pthread->active_priority)) {
+					/*
+					 * POSIX states that if the priority is
+					 * being lowered, the thread must be
+					 * inserted at the head of the queue for
+					 * its priority if it owns any priority
+					 * protection or inheritence mutexes.
+					 */
+					PTHREAD_PRIOQ_INSERT_HEAD(pthread);
+				}
+				else
+					PTHREAD_PRIOQ_INSERT_TAIL(pthread);
+			}
+
+			/*
+			 * Check for any mutex priority adjustments.  This
+			 * includes checking for a priority mutex on which
+			 * this thread is waiting.
+			 */
+			_mutex_notify_priochange(pthread);
+		}
+
+		/* Set the scheduling policy: */
+		pthread->attr.sched_policy = policy;
+
+		/*
+		 * Renable preemption and yield if a scheduling signal
+		 * arrived while in the critical region:
+		 */
+		_thread_kern_sched_undefer();
+	}
+	return(ret);
+}
+#endif