Implement kernel semaphores.

Reviewed by:	jhb

1 files changed, 177 insertions, 0 deletions

diff --git a/sys/kern/kern_sema.c b/sys/kern/kern_sema.c
new file mode 100644
index 0000000..013cddc
--- /dev/null
+++ b/sys/kern/kern_sema.c
@@ -0,0 +1,177 @@
+/*
+ * Copyright (C) 2001 Jason Evans <jasone@freebsd.org>.  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(s), this list of conditions and the following disclaimer as
+ *    the first lines of this file unmodified other than the possible 
+ *    addition of one or more copyright notices.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice(s), this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDER(S) ``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 COPYRIGHT HOLDER(S) 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.
+ *
+ * $FreeBSD$
+ */
+
+/*
+ * Counting semaphores.
+ *
+ * Priority propagation will not generally raise the priority of semaphore
+ * "owners" (a misnomer in the context of semaphores), so should not be relied
+ * upon in combination with semaphores.
+ */
+
+#include <sys/param.h>
+#include <sys/systm.h>
+#include <sys/ktr.h>
+#include <sys/condvar.h>
+#include <sys/lock.h>
+#include <sys/mutex.h>
+#include <sys/sema.h>
+
+void
+sema_init(struct sema *sema, int value, const char *description)
+{
+
+	KASSERT((value >= 0), ("%s(): negative value\n", __func__));
+
+	bzero(sema, sizeof(*sema));
+	mtx_init(&sema->sema_mtx, "sema backing lock",
+	    MTX_DEF | MTX_NOWITNESS | MTX_QUIET);
+	cv_init(&sema->sema_cv, description);
+	sema->sema_value = value;
+
+	CTR3(KTR_LOCK, __func__ "(%p, %d, \"%s\")", sema, value, description);
+}
+
+void
+sema_destroy(struct sema *sema)
+{
+
+	CTR2(KTR_LOCK, __func__ "(%p) \"%s\"", sema,
+	    cv_wmesg(&sema->sema_cv));
+
+	KASSERT((sema->sema_waiters == 0), ("%s(): waiters\n", __func__));
+
+	mtx_destroy(&sema->sema_mtx);
+	cv_destroy(&sema->sema_cv);
+}
+
+void
+_sema_post(struct sema *sema, const char *file, int line)
+{
+
+	mtx_lock(&sema->sema_mtx);
+	sema->sema_value++;
+	if (sema->sema_waiters && sema->sema_value > 0)
+		cv_signal(&sema->sema_cv);
+
+	CTR5(KTR_LOCK, __func__ "(%p) \"%s\" v = %d at %s:%d", sema,
+	    cv_wmesg(&sema->sema_cv), sema->sema_value, file, line);
+
+	mtx_unlock(&sema->sema_mtx);
+}
+
+void
+_sema_wait(struct sema *sema, const char *file, int line)
+{
+
+	mtx_lock(&sema->sema_mtx);
+	while (sema->sema_value == 0) {
+		sema->sema_waiters++;
+		cv_wait(&sema->sema_cv, &sema->sema_mtx);
+		sema->sema_waiters--;
+	}
+	sema->sema_value--;
+
+	CTR5(KTR_LOCK, __func__ "(%p) \"%s\" v = %d at %s:%d", sema,
+	    cv_wmesg(&sema->sema_cv), sema->sema_value, file, line);
+
+	mtx_unlock(&sema->sema_mtx);
+}
+
+int
+_sema_timedwait(struct sema *sema, int timo, const char *file, int line)
+{
+	int ret, timed_out;
+
+	mtx_lock(&sema->sema_mtx);
+
+	/*
+	 * A spurious wakeup will cause the timeout interval to start over.
+	 * This isn't a big deal as long as spurious wakeups don't occur
+	 * continuously, since the timeout period is merely a lower bound on how
+	 * long to wait.
+	 */
+	for (timed_out = 0; sema->sema_value == 0 && timed_out == 0;) {
+		sema->sema_waiters++;
+		timed_out = cv_timedwait(&sema->sema_cv, &sema->sema_mtx, timo);
+		sema->sema_waiters--;
+	}
+	if (sema->sema_value > 0) {
+		/* Success. */
+		sema->sema_value--;
+		ret = 1;
+
+		CTR5(KTR_LOCK, __func__ "(%p) \"%s\" v = %d at %s:%d", sema,
+		    cv_wmesg(&sema->sema_cv), sema->sema_value, file, line);
+	} else {
+		ret = 0;
+		
+		CTR4(KTR_LOCK, __func__ "(%p) \"%s\" fail at %s:%d", sema,
+		    cv_wmesg(&sema->sema_cv), file, line);
+	}
+
+	mtx_unlock(&sema->sema_mtx);
+	return (ret);
+}
+
+int
+_sema_trywait(struct sema *sema, const char *file, int line)
+{
+	int ret;
+
+	mtx_lock(&sema->sema_mtx);
+
+	if (sema->sema_value > 0) {
+		/* Success. */
+		sema->sema_value--;
+		ret = 1;
+
+		CTR5(KTR_LOCK, __func__ "(%p) \"%s\" v = %d at %s:%d", sema,
+		    cv_wmesg(&sema->sema_cv), sema->sema_value, file, line);
+	} else {
+		ret = 0;
+
+		CTR4(KTR_LOCK, __func__ "(%p) \"%s\" fail at %s:%d", sema,
+		    cv_wmesg(&sema->sema_cv), file, line);
+	}
+
+	mtx_unlock(&sema->sema_mtx);
+	return (ret);
+}
+
+int
+sema_value(struct sema *sema)
+{
+	int ret;
+
+	mtx_lock(&sema->sema_mtx);
+	ret = sema->sema_value;
+	mtx_unlock(&sema->sema_mtx);
+	return (ret);
+}