3 a46395ec 2003-10-01 devnull rendezvous - user level process synchronization
6 a46395ec 2003-10-01 devnull ulong rendezvous(ulong tag, ulong value)
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.
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.
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
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.
31 a46395ec 2003-10-01 devnull * This assumes we're using pthreads and simulates rendezvous using
32 a46395ec 2003-10-01 devnull * shared memory and mutexes.
35 a46395ec 2003-10-01 devnull #include <pthread.h>
36 a46395ec 2003-10-01 devnull #include <lib9.h>
40 a46395ec 2003-10-01 devnull VOUSHASH = 257,
43 a46395ec 2003-10-01 devnull typedef struct Vous Vous;
44 a46395ec 2003-10-01 devnull struct Vous
46 a46395ec 2003-10-01 devnull Vous *link;
48 a46395ec 2003-10-01 devnull ulong val;
49 a46395ec 2003-10-01 devnull ulong tag;
50 a46395ec 2003-10-01 devnull pthread_mutex_t mutex;
53 a46395ec 2003-10-01 devnull static void
54 a46395ec 2003-10-01 devnull ign(int x)
59 a46395ec 2003-10-01 devnull void /*__attribute__((constructor))*/
60 a46395ec 2003-10-01 devnull ignusr1(void)
62 a46395ec 2003-10-01 devnull signal(SIGUSR1, ign);
65 a46395ec 2003-10-01 devnull static Vous vouspool[2048];
66 a46395ec 2003-10-01 devnull static int nvousused;
67 a46395ec 2003-10-01 devnull static Vous *vousfree;
68 a46395ec 2003-10-01 devnull static Vous *voushash[VOUSHASH];
69 a46395ec 2003-10-01 devnull static Lock vouslock;
71 a46395ec 2003-10-01 devnull static Vous*
72 a46395ec 2003-10-01 devnull getvous(void)
76 a46395ec 2003-10-01 devnull if(vousfree){
77 a46395ec 2003-10-01 devnull v = vousfree;
78 a46395ec 2003-10-01 devnull vousfree = v->link;
79 a46395ec 2003-10-01 devnull }else if(nvousused < nelem(vouspool)){
80 a46395ec 2003-10-01 devnull v = &vouspool[nvousused++];
81 a46395ec 2003-10-01 devnull pthread_mutex_init(&v->mutex, NULL);
84 a46395ec 2003-10-01 devnull return v;
87 a46395ec 2003-10-01 devnull static void
88 a46395ec 2003-10-01 devnull putvous(Vous *v)
90 a46395ec 2003-10-01 devnull lock(&vouslock);
91 a46395ec 2003-10-01 devnull v->link = vousfree;
92 a46395ec 2003-10-01 devnull vousfree = v;
93 a46395ec 2003-10-01 devnull unlock(&vouslock);
96 a46395ec 2003-10-01 devnull static Vous*
97 a46395ec 2003-10-01 devnull findvous(ulong tag, ulong val, int *found)
100 a46395ec 2003-10-01 devnull Vous *v, **l;
102 a46395ec 2003-10-01 devnull lock(&vouslock);
103 a46395ec 2003-10-01 devnull h = tag%VOUSHASH;
104 a46395ec 2003-10-01 devnull for(l=&voushash[h], v=*l; v; l=&(*l)->link, v=*l){
105 a46395ec 2003-10-01 devnull if(v->tag == tag){
106 a46395ec 2003-10-01 devnull *l = v->link;
107 a46395ec 2003-10-01 devnull *found = 1;
108 a46395ec 2003-10-01 devnull unlock(&vouslock);
109 a46395ec 2003-10-01 devnull return v;
112 a46395ec 2003-10-01 devnull v = getvous();
113 a46395ec 2003-10-01 devnull v->link = voushash[h];
114 a46395ec 2003-10-01 devnull v->val = val;
115 a46395ec 2003-10-01 devnull v->tag = tag;
116 a46395ec 2003-10-01 devnull lock(&v->lk);
117 a46395ec 2003-10-01 devnull voushash[h] = v;
118 a46395ec 2003-10-01 devnull unlock(&vouslock);
119 a46395ec 2003-10-01 devnull *found = 0;
120 a46395ec 2003-10-01 devnull return v;
123 a46395ec 2003-10-01 devnull #define DBG 0
125 a46395ec 2003-10-01 devnull rendezvous(ulong tag, ulong val)
127 a46395ec 2003-10-01 devnull int found;
128 a46395ec 2003-10-01 devnull ulong rval;
129 a46395ec 2003-10-01 devnull Vous *v;
131 a46395ec 2003-10-01 devnull v = findvous(tag, val, &found);
132 a46395ec 2003-10-01 devnull if(!found){
133 a46395ec 2003-10-01 devnull if(DBG)fprint(2, "tag %lux, sleeping on %p\n", tag, v);
135 a46395ec 2003-10-01 devnull * No rendezvous partner was found; the next guy
136 a46395ec 2003-10-01 devnull * through will find v and wake us, so we must go
137 a46395ec 2003-10-01 devnull * to sleep. Do this by locking the mutex (it is
138 a46395ec 2003-10-01 devnull * unlocked) and then locking it again (our waker will
139 a46395ec 2003-10-01 devnull * unlock it for us).
141 a46395ec 2003-10-01 devnull if(pthread_mutex_lock(&v->mutex) != 0)
142 a46395ec 2003-10-01 devnull abort();
143 a46395ec 2003-10-01 devnull unlock(&v->lk);
144 a46395ec 2003-10-01 devnull if(pthread_mutex_lock(&v->mutex) != 0)
145 a46395ec 2003-10-01 devnull abort();
146 a46395ec 2003-10-01 devnull rval = v->val;
147 a46395ec 2003-10-01 devnull pthread_mutex_unlock(&v->mutex);
148 a46395ec 2003-10-01 devnull if(DBG)fprint(2, " awake on %p\n", v);
149 a46395ec 2003-10-01 devnull unlock(&v->lk);
150 a46395ec 2003-10-01 devnull putvous(v);
153 a46395ec 2003-10-01 devnull * Found someone to meet. Wake him:
155 a46395ec 2003-10-01 devnull * A. lock v->lk (waits for him to lock the mutex once.
156 a46395ec 2003-10-01 devnull * B. unlock the mutex (wakes him up)
158 a46395ec 2003-10-01 devnull if(DBG)fprint(2, "found tag %lux on %p, waking\n", tag, v);
159 a46395ec 2003-10-01 devnull lock(&v->lk);
160 a46395ec 2003-10-01 devnull rval = v->val;
161 a46395ec 2003-10-01 devnull v->val = val;
162 a46395ec 2003-10-01 devnull if(pthread_mutex_unlock(&v->mutex) != 0)
163 a46395ec 2003-10-01 devnull abort();
164 a46395ec 2003-10-01 devnull /* lock passes to him */
166 a46395ec 2003-10-01 devnull return rval;
