From mboxrd@z Thu Jan  1 00:00:00 1970
Date: Fri, 23 Aug 1996 18:03:29 -0400
From: philw@plan9.bell-labs.com philw@plan9.bell-labs.com
Subject: No subject
Topicbox-Message-UUID: 4b739b66-eac8-11e9-9e20-41e7f4b1d025
Message-ID: <19960823220329.eevL9V7Bid8PkNAUmx9jvbigH-nDN-7tefrzVMRQYh8@z>

Put this in the library ...
philw.

#include <alef.h>

/*
 * Multiple readers/Single Write lock package
*/

void
RWlock.Rlock(RWlock *l)
{
	l->x.lock();		/* wait here for writers and exclusion */
	l->lock();
	l->readers++;
	l->k.canlock();		/* block writers if we are the first reader */
	l->unlock();
	l->x.unlock();
}

void
RWlock.Runlock(RWlock *l)
{
	l->lock();
	if(--l->readers == 0)	/* last reader out allows writers */
		l->k.unlock();
	l->unlock();
}

void
RWlock.Wlock(RWlock *l)
{
	l->x.lock();		/* wait here for writers and exclusion */
	l->k.lock();		/* wait here for last reader */
}

void
RWlock.Wunlock(RWlock *l)
{
	l->k.unlock();
	l->x.unlock();
}