From: dlg <dlg@openbsd.org>
Date: Thu, 14 Dec 2017 00:41:58 +0000 (+0000)
Subject: add code to provide simple wait condition handling.
X-Git-Url: http://artulab.com/gitweb/?a=commitdiff_plain;h=0d158b2bc03d5e86f4220bdfdd06967891b50c6f;p=openbsd

add code to provide simple wait condition handling.

this will be used to replace the bare sleep_state handling in a
bunch of places, starting with the barriers.
---

diff --git a/share/man/man9/Makefile b/share/man/man9/Makefile
index 98760385c02..b9942f0bd27 100644
--- a/share/man/man9/Makefile
+++ b/share/man/man9/Makefile
@@ -1,4 +1,4 @@
-#	$OpenBSD: Makefile,v 1.287 2017/06/19 23:44:11 dlg Exp $
+#	$OpenBSD: Makefile,v 1.288 2017/12/14 00:41:58 dlg Exp $
 #	$NetBSD: Makefile,v 1.4 1996/01/09 03:23:01 thorpej Exp $
 
 #	Makefile for section 9 (kernel function and variable) manual pages.
@@ -9,8 +9,8 @@ MAN=	aml_evalnode.9 atomic_add_int.9 atomic_cas_uint.9 \
 	audio.9 autoconf.9 \
 	bemtoh32.9 bio_register.9 boot.9 bpf_mtap.9 buffercache.9 bufq_init.9 \
 	bus_dma.9 bus_space.9 \
-	copy.9 config_attach.9 config_defer.9 counters_alloc.9 cpumem_get.9 \
-	crypto.9 \
+	copy.9 cond_init.9 config_attach.9 config_defer.9 counters_alloc.9 \
+	cpumem_get.9 crypto.9 \
 	delay.9 disk.9 disklabel.9 dma_alloc.9 dohooks.9 \
 	dostartuphooks.9 \
 	evcount.9 extent.9 fb_setup.9 file.9 fork1.9 \
diff --git a/share/man/man9/cond_init.9 b/share/man/man9/cond_init.9
new file mode 100644
index 00000000000..1f6ff24d24c
--- /dev/null
+++ b/share/man/man9/cond_init.9
@@ -0,0 +1,108 @@
+.\"	$OpenBSD: cond_init.9,v 1.1 2017/12/14 00:41:58 dlg Exp $ */
+.\"
+.\" Copyright (c) 2017 David Gwynne <dlg@openbsd.org>
+.\"
+.\" Permission to use, copy, modify, and distribute this software for any
+.\" purpose with or without fee is hereby granted, provided that the above
+.\" copyright notice and this permission notice appear in all copies.
+.\"
+.\" THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+.\" WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+.\" MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+.\" ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+.\" WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+.\" ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+.\" OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+.\"
+.Dd $Mdocdate: December 14 2017 $
+.Dt COND_INIT 9
+.Os
+.Sh NAME
+.Nm cond_init ,
+.Nm cond_wait ,
+.Nm cond_signal ,
+.Nm COND_INITIALIZER
+.Nd wait condition API
+.Sh SYNOPSIS
+.In sys/systm.h
+.Ft void
+.Fn "cond_init" "struct cond *c"
+.Ft void
+.Fn "cond_wait" "struct cond *c" "const char *wmesg"
+.Ft void
+.Fn "cond_signal" "struct cond *c"
+.Fn "COND_INITIALIZER"
+.Sh DESCRIPTION
+The wait condition API allows a thread to sleep while it waits for
+a notification, aka signal, that pending work has completed.
+.Pp
+.Fn cond_init
+initialises the wait condition
+.Fa c
+for use.
+.Pp
+.Fn cond_wait
+is used to sleep on the wait condition
+.Fa c
+until whatever the thread is waiting on calls
+.Fa cond_signal .
+.Fa wmesg
+is a pointer to a character string indicating the reason the thread
+is sleeping.
+.Pp
+.Fa cond_signal
+is used to notify the thread waiting on
+.Fa c
+that the work has finished and it may proceed.
+.Pp
+.Fn COND_INITIALIZER
+initialises a declaration of a cond for use.
+.Sh CONTEXT
+.Fn cond_init ,
+and
+.Fn cond_signal
+can be called during autoconf, from process context, or from interrupt
+context.
+.Pp
+.Fn cond_wait
+can be called from process context.
+.Sh EXAMPLES
+.Xr taskq_barrier 9
+is implemented using the wait condition API.
+The following is a commented copy of the implementation:
+.Bd -literal
+static void	taskq_barrier_task(void *);
+
+void
+taskq_barrier(struct taskq *tq)
+{
+	struct cond c;
+	struct task t;
+
+	/*
+	 * any currently running work has to have finished
+	 * before this new task can be run.
+	 */
+
+	cond_init(&c);
+	task_init(&t, taskq_barrier_task, &c);
+
+	task_add(tq, &t);
+
+	/* wait until the task runs and signals completion */
+	cond_wait(&c, "tqbar");
+}
+
+static void
+taskq_barrier_task(void *p)
+{
+	struct cond *c = p;
+
+	/*
+	 * all previous tasks have run, signal the thread waiting
+	 * in taskq_barrier
+	 */
+
+	cond_signal(c);
+} 
+.Ed
diff --git a/sys/kern/kern_synch.c b/sys/kern/kern_synch.c
index 7fb23449560..ea28288d375 100644
--- a/sys/kern/kern_synch.c
+++ b/sys/kern/kern_synch.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: kern_synch.c,v 1.142 2017/12/04 09:38:20 mpi Exp $	*/
+/*	$OpenBSD: kern_synch.c,v 1.143 2017/12/14 00:41:58 dlg Exp $	*/
 /*	$NetBSD: kern_synch.c,v 1.37 1996/04/22 01:38:37 christos Exp $	*/
 
 /*
@@ -704,3 +704,31 @@ refcnt_finalize(struct refcnt *r, const char *wmesg)
 		sleep_finish(&sls, refcnt);
 	}
 }
+
+void
+cond_init(struct cond *c)
+{
+	c->c_wait = 1;
+}
+
+void
+cond_signal(struct cond *c)
+{
+	c->c_wait = 0;
+
+	wakeup_one(c);
+}
+
+void
+cond_wait(struct cond *c, const char *wmesg)
+{
+	struct sleep_state sls;
+	int wait;
+
+	wait = c->c_wait;
+	while (wait) {
+		sleep_setup(&sls, c, PWAIT, wmesg);
+		wait = c->c_wait;
+		sleep_finish(&sls, wait);
+	}
+}
diff --git a/sys/sys/proc.h b/sys/sys/proc.h
index d65efbfd486..1addf7529cd 100644
--- a/sys/sys/proc.h
+++ b/sys/sys/proc.h
@@ -1,4 +1,4 @@
-/*	$OpenBSD: proc.h,v 1.242 2017/12/12 07:55:36 deraadt Exp $	*/
+/*	$OpenBSD: proc.h,v 1.243 2017/12/14 00:41:58 dlg Exp $	*/
 /*	$NetBSD: proc.h,v 1.44 1996/04/22 01:23:21 christos Exp $	*/
 
 /*-
@@ -557,6 +557,12 @@ struct sleep_state {
 	int sls_sig;
 };
 
+struct cond {
+	int	c_wait;
+};
+
+#define COND_INITIALIZER()		{ 1 }
+
 #if defined(MULTIPROCESSOR)
 void	proc_trampoline_mp(void);	/* XXX */
 #endif
diff --git a/sys/sys/systm.h b/sys/sys/systm.h
index 82abf9b873e..04326d9db38 100644
--- a/sys/sys/systm.h
+++ b/sys/sys/systm.h
@@ -1,4 +1,4 @@
-/*	$OpenBSD: systm.h,v 1.135 2017/11/13 14:41:46 mpi Exp $	*/
+/*	$OpenBSD: systm.h,v 1.136 2017/12/14 00:41:58 dlg Exp $	*/
 /*	$NetBSD: systm.h,v 1.50 1996/06/09 04:55:09 briggs Exp $	*/
 
 /*-
@@ -247,6 +247,11 @@ int	sleep_finish_timeout(struct sleep_state *);
 int	sleep_finish_signal(struct sleep_state *);
 void	sleep_queue_init(void);
 
+struct cond;
+void	cond_init(struct cond *);
+void	cond_wait(struct cond *, const char *);
+void	cond_signal(struct cond *);
+
 struct mutex;
 struct rwlock;
 void    wakeup_n(const volatile void *, int);