1 a46395ec 2003-10-01 devnull /*
  2 a46395ec 2003-10-01 devnull      NAME
  3 a46395ec 2003-10-01 devnull           rendezvous - user level process synchronization
  4 a46395ec 2003-10-01 devnull 
  5 a46395ec 2003-10-01 devnull      SYNOPSIS
  6 a46395ec 2003-10-01 devnull           ulong rendezvous(ulong tag, ulong value)
  7 a46395ec 2003-10-01 devnull 
  8 a46395ec 2003-10-01 devnull      DESCRIPTION
  9 a46395ec 2003-10-01 devnull           The rendezvous system call allows two processes to synchro-
 10 a46395ec 2003-10-01 devnull           nize and exchange a value.  In conjunction with the shared
 11 a46395ec 2003-10-01 devnull           memory system calls (see segattach(2) and fork(2)), it
 12 a46395ec 2003-10-01 devnull           enables parallel programs to control their scheduling.
 13 a46395ec 2003-10-01 devnull 
 14 a46395ec 2003-10-01 devnull           Two processes wishing to synchronize call rendezvous with a
 15 a46395ec 2003-10-01 devnull           common tag, typically an address in memory they share.  One
 16 a46395ec 2003-10-01 devnull           process will arrive at the rendezvous first; it suspends
 17 a46395ec 2003-10-01 devnull           execution until a second arrives.  When a second process
 18 a46395ec 2003-10-01 devnull           meets the rendezvous the value arguments are exchanged
 19 a46395ec 2003-10-01 devnull           between the processes and returned as the result of the
 20 a46395ec 2003-10-01 devnull           respective rendezvous system calls.  Both processes are
 21 a46395ec 2003-10-01 devnull           awakened when the rendezvous succeeds.
 22 a46395ec 2003-10-01 devnull 
 23 a46395ec 2003-10-01 devnull           The set of tag values which two processes may use to
 24 a46395ec 2003-10-01 devnull           rendezvous-their tag space-is inherited when a process
 25 a46395ec 2003-10-01 devnull           forks, unless RFREND is set in the argument to rfork; see
 26 a46395ec 2003-10-01 devnull           fork(2).
 27 a46395ec 2003-10-01 devnull 
 28 a46395ec 2003-10-01 devnull           If a rendezvous is interrupted the return value is ~0, so
 29 a46395ec 2003-10-01 devnull           that value should not be used in normal communication.
 30 a46395ec 2003-10-01 devnull 
 31 a46395ec 2003-10-01 devnull  * This simulates rendezvous with shared memory, pause, and SIGUSR1.
 32 a46395ec 2003-10-01 devnull  */
 33 a46395ec 2003-10-01 devnull 
 34 a46395ec 2003-10-01 devnull #include <signal.h>
 35 a46395ec 2003-10-01 devnull #include <lib9.h>
 36 a46395ec 2003-10-01 devnull 
 37 a46395ec 2003-10-01 devnull enum
 38 a46395ec 2003-10-01 devnull {
 39 a46395ec 2003-10-01 devnull 	VOUSHASH = 257,
 40 a46395ec 2003-10-01 devnull };
 41 a46395ec 2003-10-01 devnull 
 42 a46395ec 2003-10-01 devnull typedef struct Vous Vous;
 43 a46395ec 2003-10-01 devnull struct Vous
 44 a46395ec 2003-10-01 devnull {
 45 a46395ec 2003-10-01 devnull 	Vous *link;
 46 a46395ec 2003-10-01 devnull 	Lock lk;
 47 a46395ec 2003-10-01 devnull 	int pid;
 48 a46395ec 2003-10-01 devnull 	ulong val;
 49 a46395ec 2003-10-01 devnull 	ulong tag;
 50 a46395ec 2003-10-01 devnull };
 51 a46395ec 2003-10-01 devnull 
 52 a46395ec 2003-10-01 devnull static void
 53 a46395ec 2003-10-01 devnull ign(int x)
 54 a46395ec 2003-10-01 devnull {
 55 a46395ec 2003-10-01 devnull 	USED(x);
 56 a46395ec 2003-10-01 devnull }
 57 a46395ec 2003-10-01 devnull 
 58 a46395ec 2003-10-01 devnull void /*__attribute__((constructor))*/
 59 a46395ec 2003-10-01 devnull ignusr1(void)
 60 a46395ec 2003-10-01 devnull {
 61 a46395ec 2003-10-01 devnull 	signal(SIGUSR1, ign);
 62 a46395ec 2003-10-01 devnull }
 63 a46395ec 2003-10-01 devnull 
 64 a46395ec 2003-10-01 devnull static Vous vouspool[2048];
 65 a46395ec 2003-10-01 devnull static int nvousused;
 66 a46395ec 2003-10-01 devnull static Vous *vousfree;
 67 a46395ec 2003-10-01 devnull static Vous *voushash[VOUSHASH];
 68 a46395ec 2003-10-01 devnull static Lock vouslock;
 69 a46395ec 2003-10-01 devnull 
 70 a46395ec 2003-10-01 devnull static Vous*
 71 a46395ec 2003-10-01 devnull getvous(void)
 72 a46395ec 2003-10-01 devnull {
 73 a46395ec 2003-10-01 devnull 	Vous *v;
 74 a46395ec 2003-10-01 devnull 
 75 a46395ec 2003-10-01 devnull 	if(vousfree){
 76 a46395ec 2003-10-01 devnull 		v = vousfree;
 77 a46395ec 2003-10-01 devnull 		vousfree = v->link;
 78 a46395ec 2003-10-01 devnull 	}else if(nvousused < nelem(vouspool))
 79 a46395ec 2003-10-01 devnull 		v = &vouspool[nvousused++];
 80 a46395ec 2003-10-01 devnull 	else
 81 a46395ec 2003-10-01 devnull 		abort();
 82 a46395ec 2003-10-01 devnull 	return v;
 83 a46395ec 2003-10-01 devnull }
 84 a46395ec 2003-10-01 devnull 
 85 a46395ec 2003-10-01 devnull static void
 86 a46395ec 2003-10-01 devnull putvous(Vous *v)
 87 a46395ec 2003-10-01 devnull {
 88 a46395ec 2003-10-01 devnull 	lock(&vouslock);
 89 a46395ec 2003-10-01 devnull 	v->link = vousfree;
 90 a46395ec 2003-10-01 devnull 	vousfree = v;
 91 a46395ec 2003-10-01 devnull 	unlock(&vouslock);
 92 a46395ec 2003-10-01 devnull }
 93 a46395ec 2003-10-01 devnull 
 94 a46395ec 2003-10-01 devnull static Vous*
 95 a46395ec 2003-10-01 devnull findvous(ulong tag, ulong val, int pid)
 96 a46395ec 2003-10-01 devnull {
 97 a46395ec 2003-10-01 devnull 	int h;
 98 a46395ec 2003-10-01 devnull 	Vous *v, **l;
 99 a46395ec 2003-10-01 devnull 
100 a46395ec 2003-10-01 devnull 	lock(&vouslock);
101 a46395ec 2003-10-01 devnull 	h = tag%VOUSHASH;
102 a46395ec 2003-10-01 devnull 	for(l=&voushash[h], v=*l; v; l=&(*l)->link, v=*l){
103 a46395ec 2003-10-01 devnull 		if(v->tag == tag){
104 a46395ec 2003-10-01 devnull 			*l = v->link;
105 a46395ec 2003-10-01 devnull 			unlock(&vouslock);
106 a46395ec 2003-10-01 devnull 			return v;
107 a46395ec 2003-10-01 devnull 		}
108 a46395ec 2003-10-01 devnull 	}
109 a46395ec 2003-10-01 devnull 	v = getvous();
110 a46395ec 2003-10-01 devnull 	v->pid = pid;
111 a46395ec 2003-10-01 devnull 	v->link = voushash[h];
112 a46395ec 2003-10-01 devnull 	v->val = val;
113 a46395ec 2003-10-01 devnull 	v->tag = tag;
114 a46395ec 2003-10-01 devnull 	lock(&v->lk);
115 a46395ec 2003-10-01 devnull 	voushash[h] = v;
116 a46395ec 2003-10-01 devnull 	unlock(&vouslock);
117 a46395ec 2003-10-01 devnull 	return v;
118 a46395ec 2003-10-01 devnull }
119 a46395ec 2003-10-01 devnull 
120 a46395ec 2003-10-01 devnull #define DBG 0
121 a46395ec 2003-10-01 devnull ulong
122 a46395ec 2003-10-01 devnull rendezvous(ulong tag, ulong val)
123 a46395ec 2003-10-01 devnull {
124 a46395ec 2003-10-01 devnull 	int me, vpid;
125 a46395ec 2003-10-01 devnull 	ulong rval;
126 a46395ec 2003-10-01 devnull 	Vous *v;
127 a46395ec 2003-10-01 devnull 	sigset_t mask;
128 a46395ec 2003-10-01 devnull 
129 a46395ec 2003-10-01 devnull 	me = getpid();
130 a46395ec 2003-10-01 devnull 	v = findvous(tag, val, me);
131 a46395ec 2003-10-01 devnull 	if(v->pid == me){
132 a46395ec 2003-10-01 devnull 		if(DBG)fprint(2, "pid is %d tag %lux, sleeping\n", me, tag);
133 a46395ec 2003-10-01 devnull 		/*
134 a46395ec 2003-10-01 devnull 		 * No rendezvous partner was found; the next guy
135 a46395ec 2003-10-01 devnull 		 * through will find v and wake us, so we must go
136 a46395ec 2003-10-01 devnull 		 * to sleep.
137 a46395ec 2003-10-01 devnull 		 *
138 a46395ec 2003-10-01 devnull 		 * To go to sleep:
139 a46395ec 2003-10-01 devnull 		 *	1. disable USR1 signals.
140 a46395ec 2003-10-01 devnull 		 *	2. unlock v->lk (tells waker okay to signal us).
141 a46395ec 2003-10-01 devnull 		 *	3. atomically suspend and enable USR1 signals.
142 a46395ec 2003-10-01 devnull 		 *
143 a46395ec 2003-10-01 devnull 		 * The call to ignusr1() could be done once at 
144 a46395ec 2003-10-01 devnull 		 * process creation instead of every time through rendezvous.
145 a46395ec 2003-10-01 devnull 		 */
146 a46395ec 2003-10-01 devnull 		v->val = val;
147 a46395ec 2003-10-01 devnull 		ignusr1();
148 a46395ec 2003-10-01 devnull 		sigprocmask(SIG_SETMASK, NULL, &mask);
149 a46395ec 2003-10-01 devnull 		sigaddset(&mask, SIGUSR1);
150 a46395ec 2003-10-01 devnull 		sigprocmask(SIG_SETMASK, &mask, NULL);
151 a46395ec 2003-10-01 devnull 		sigdelset(&mask, SIGUSR1);
152 a46395ec 2003-10-01 devnull 		unlock(&v->lk);
153 a46395ec 2003-10-01 devnull 		sigsuspend(&mask);
154 a46395ec 2003-10-01 devnull 		rval = v->val;
155 a46395ec 2003-10-01 devnull 		if(DBG)fprint(2, "pid is %d, awake\n", me);
156 a46395ec 2003-10-01 devnull 		putvous(v);
157 a46395ec 2003-10-01 devnull 	}else{
158 a46395ec 2003-10-01 devnull 		/*
159 a46395ec 2003-10-01 devnull 		 * Found someone to meet.  Wake him:
160 a46395ec 2003-10-01 devnull 		 *
161 a46395ec 2003-10-01 devnull 		 *	A. lock v->lk (waits for him to get to his step 2)
162 a46395ec 2003-10-01 devnull 		 *	B. send a USR1
163 a46395ec 2003-10-01 devnull 		 *
164 a46395ec 2003-10-01 devnull 		 * He won't get the USR1 until he suspends, which
165 a46395ec 2003-10-01 devnull 		 * means it must wake him up (it can't get delivered
166 a46395ec 2003-10-01 devnull 		 * before he sleeps).
167 a46395ec 2003-10-01 devnull 		 */
168 a46395ec 2003-10-01 devnull 		vpid = v->pid;
169 a46395ec 2003-10-01 devnull 		lock(&v->lk);
170 a46395ec 2003-10-01 devnull 		rval = v->val;
171 a46395ec 2003-10-01 devnull 		v->val = val;
172 a46395ec 2003-10-01 devnull 		unlock(&v->lk);
173 a46395ec 2003-10-01 devnull 		if(kill(vpid, SIGUSR1) < 0){
174 a46395ec 2003-10-01 devnull 			if(DBG)fprint(2, "pid is %d, kill %d failed: %r\n", me, vpid);
175 a46395ec 2003-10-01 devnull 			abort();
176 a46395ec 2003-10-01 devnull 		}
177 a46395ec 2003-10-01 devnull 	}
178 a46395ec 2003-10-01 devnull 	return rval;
179 a46395ec 2003-10-01 devnull }
180 a46395ec 2003-10-01 devnull