1 #include "threadimpl.h"
2 
3 /*
4  * One can go through a lot of effort to avoid this global lock.
5  * You have to put locks in all the channels and all the Alt
6  * structures.  At the beginning of an alt you have to lock all
7  * the channels, but then to try to actually exec an op you
8  * have to lock the other guy's alt structure, so that other 
9  * people aren't trying to use him in some other op at the
10  * same time.
11  * 
12  * For Plan 9 apps, it's just not worth the extra effort.
13  */
14 static QLock chanlock;
15 
16 Channel*
17 chancreate(int elemsize, int bufsize)
18 {
19 	Channel *c;
20 
21 	c = malloc(sizeof *c+bufsize*elemsize);
22 	if(c == nil)
23 		sysfatal("chancreate malloc: %r");
24 	memset(c, 0, sizeof *c);
25 	c->elemsize = elemsize;
26 	c->bufsize = bufsize;
27 	c->nbuf = 0;
28 	c->buf = (uchar*)(c+1);
29 	return c;
30 }
31 
32 void
33 chansetname(Channel *c, char *fmt, ...)
34 {
35 	char *name;
36 	va_list arg;
37 
38 	va_start(arg, fmt);
39 	name = vsmprint(fmt, arg);
40 	va_end(arg);
41 	free(c->name);
42 	c->name = name;
43 }
44 
45 /* bug - work out races */
46 void
47 chanfree(Channel *c)
48 {
49 	if(c == nil)
50 		return;
51 	free(c->name);
52 	free(c->arecv.a);
53 	free(c->asend.a);
54 	free(c);
55 }
56 
57 static void
58 addarray(_Altarray *a, Alt *alt)
59 {
60 	if(a->n == a->m){
61 		a->m += 16;
62 		a->a = realloc(a->a, a->m*sizeof a->a[0]);
63 	}
64 	a->a[a->n++] = alt;
65 }
66 
67 static void
68 delarray(_Altarray *a, int i)
69 {
70 	--a->n;
71 	a->a[i] = a->a[a->n];
72 }
73 
74 /*
75  * doesn't really work for things other than CHANSND and CHANRCV
76  * but is only used as arg to chanarray, which can handle it
77  */
78 #define otherop(op)	(CHANSND+CHANRCV-(op))
79 
80 static _Altarray*
81 chanarray(Channel *c, uint op)
82 {
83 	switch(op){
84 	default:
85 		return nil;
86 	case CHANSND:
87 		return &c->asend;
88 	case CHANRCV:
89 		return &c->arecv;
90 	}
91 }
92 
93 static int
94 altcanexec(Alt *a)
95 {
96 	_Altarray *ar;
97 	Channel *c;
98 
99 	if(a->op == CHANNOP)
100 		return 0;
101 	c = a->c;
102 	if(c->bufsize == 0){
103 		ar = chanarray(c, otherop(a->op));
104 		return ar && ar->n;
105 	}else{
106 		switch(a->op){
107 		default:
108 			return 0;
109 		case CHANSND:
110 			return c->nbuf < c->bufsize;
111 		case CHANRCV:
112 			return c->nbuf > 0;
113 		}
114 	}
115 }
116 
117 static void
118 altqueue(Alt *a)
119 {
120 	_Altarray *ar;
121 
122 	ar = chanarray(a->c, a->op);
123 	addarray(ar, a);
124 }
125 
126 static void
127 altdequeue(Alt *a)
128 {
129 	int i;
130 	_Altarray *ar;
131 
132 	ar = chanarray(a->c, a->op);
133 	if(ar == nil){
134 		fprint(2, "bad use of altdequeue op=%d\n", a->op);
135 		abort();
136 	}
137 
138 	for(i=0; i<ar->n; i++)
139 		if(ar->a[i] == a){
140 			delarray(ar, i);
141 			return;
142 		}
143 	fprint(2, "cannot find self in altdq\n");
144 	abort();
145 }
146 
147 static void
148 altalldequeue(Alt *a)
149 {
150 	int i;
151 
152 	for(i=0; a[i].op!=CHANEND && a[i].op!=CHANNOBLK; i++)
153 		if(a[i].op != CHANNOP)
154 			altdequeue(&a[i]);
155 }
156 
157 static void
158 amove(void *dst, void *src, uint n)
159 {
160 	if(dst){
161 		if(src == nil)
162 			memset(dst, 0, n);
163 		else
164 			memmove(dst, src, n);
165 	}
166 }
167 
168 /*
169  * Actually move the data around.  There are up to three
170  * players: the sender, the receiver, and the channel itself.
171  * If the channel is unbuffered or the buffer is empty,
172  * data goes from sender to receiver.  If the channel is full,
173  * the receiver removes some from the channel and the sender
174  * gets to put some in.
175  */
176 static void
177 altcopy(Alt *s, Alt *r)
178 {
179 	Alt *t;
180 	Channel *c;
181 	uchar *cp;
182 
183 	/*
184 	 * Work out who is sender and who is receiver
185 	 */
186 	if(s == nil && r == nil)
187 		return;
188 	assert(s != nil);
189 	c = s->c;
190 	if(s->op == CHANRCV){
191 		t = s;
192 		s = r;
193 		r = t;
194 	}
195 	assert(s==nil || s->op == CHANSND);
196 	assert(r==nil || r->op == CHANRCV);
197 
198 	/*
199 	 * Channel is empty (or unbuffered) - copy directly.
200 	 */
201 	if(s && r && c->nbuf == 0){
202 		amove(r->v, s->v, c->elemsize);
203 		return;
204 	}
205 
206 	/*
207 	 * Otherwise it's always okay to receive and then send.
208 	 */
209 	if(r){
210 		cp = c->buf + c->off*c->elemsize;
211 		amove(r->v, cp, c->elemsize);
212 		--c->nbuf;
213 		if(++c->off == c->bufsize)
214 			c->off = 0;
215 	}
216 	if(s){
217 		cp = c->buf + (c->off+c->nbuf)%c->bufsize*c->elemsize;
218 		amove(cp, s->v, c->elemsize);
219 		++c->nbuf;
220 	}
221 }
222 
223 static void
224 altexec(Alt *a)
225 {
226 	int i;
227 	_Altarray *ar;
228 	Alt *other;
229 	Channel *c;
230 
231 	c = a->c;
232 	ar = chanarray(c, otherop(a->op));
233 	if(ar && ar->n){
234 		i = rand()%ar->n;
235 		other = ar->a[i];
236 		altcopy(a, other);
237 		altalldequeue(other->xalt);
238 		other->xalt[0].xalt = other;
239 		_threadready(other->thread);
240 	}else
241 		altcopy(a, nil);
242 }
243 
244 #define dbgalt 0
245 int
246 chanalt(Alt *a)
247 {
248 	int i, j, ncan, n, canblock;
249 	Channel *c;
250 	_Thread *t;
251 
252 	needstack(512);
253 	for(i=0; a[i].op != CHANEND && a[i].op != CHANNOBLK; i++)
254 		;
255 	n = i;
256 	canblock = a[i].op == CHANEND;
257 
258 	t = proc()->thread;
259 	for(i=0; i<n; i++){
260 		a[i].thread = t;
261 		a[i].xalt = a;
262 	}
263 	qlock(&chanlock);
264 if(dbgalt) print("alt ");
265 	ncan = 0;
266 	for(i=0; i<n; i++){
267 		c = a[i].c;
268 if(dbgalt) print(" %c:", "esrnb"[a[i].op]);
269 if(dbgalt) if(c->name) print("%s", c->name); else print("%p", c);
270 		if(altcanexec(&a[i])){
271 if(dbgalt) print("*");
272 			ncan++;
273 		}
274 	}
275 	if(ncan){
276 		j = rand()%ncan;
277 		for(i=0; i<n; i++){
278 			if(altcanexec(&a[i])){
279 				if(j-- == 0){
280 if(dbgalt){
281 c = a[i].c;
282 print(" => %c:", "esrnb"[a[i].op]);
283 if(c->name) print("%s", c->name); else print("%p", c);
284 print("\n");
285 }
286 					altexec(&a[i]);
287 					qunlock(&chanlock);
288 					return i;
289 				}
290 			}
291 		}
292 	}
293 if(dbgalt)print("\n");
294 
295 	if(!canblock){
296 		qunlock(&chanlock);
297 		return -1;
298 	}
299 
300 	for(i=0; i<n; i++){
301 		if(a[i].op != CHANNOP)
302 			altqueue(&a[i]);
303 	}
304 	qunlock(&chanlock);
305 
306 	_threadswitch();
307 
308 	/*
309 	 * the guy who ran the op took care of dequeueing us
310 	 * and then set a[0].alt to the one that was executed.
311 	 */
312 	return a[0].xalt - a;
313 }
314 
315 static int
316 _chanop(Channel *c, int op, void *p, int canblock)
317 {
318 	Alt a[2];
319 
320 	a[0].c = c;
321 	a[0].op = op;
322 	a[0].v = p;
323 	a[1].op = canblock ? CHANEND : CHANNOBLK;
324 	if(chanalt(a) < 0)
325 		return -1;
326 	return 1;
327 }
328 
329 int
330 chansend(Channel *c, void *v)
331 {
332 	return _chanop(c, CHANSND, v, 1);
333 }
334 
335 int
336 channbsend(Channel *c, void *v)
337 {
338 	return _chanop(c, CHANSND, v, 0);
339 }
340 
341 int
342 chanrecv(Channel *c, void *v)
343 {
344 	return _chanop(c, CHANRCV, v, 1);
345 }
346 
347 int
348 channbrecv(Channel *c, void *v)
349 {
350 	return _chanop(c, CHANRCV, v, 0);
351 }
352 
353 int
354 chansendp(Channel *c, void *v)
355 {
356 	return _chanop(c, CHANSND, (void*)&v, 1);
357 }
358 
359 void*
360 chanrecvp(Channel *c)
361 {
362 	void *v;
363 
364 	_chanop(c, CHANRCV, (void*)&v, 1);
365 	return v;
366 }
367 
368 int
369 channbsendp(Channel *c, void *v)
370 {
371 	return _chanop(c, CHANSND, (void*)&v, 0);
372 }
373 
374 void*
375 channbrecvp(Channel *c)
376 {
377 	void *v;
378 
379 	_chanop(c, CHANRCV, (void*)&v, 0);
380 	return v;
381 }
382 
383 int
384 chansendul(Channel *c, ulong val)
385 {
386 	return _chanop(c, CHANSND, &val, 1);
387 }
388 
389 ulong
390 chanrecvul(Channel *c)
391 {
392 	ulong val;
393 
394 	_chanop(c, CHANRCV, &val, 1);
395 	return val;
396 }
397 
398 int
399 channbsendul(Channel *c, ulong val)
400 {
401 	return _chanop(c, CHANSND, &val, 0);
402 }
403 
404 ulong
405 channbrecvul(Channel *c)
406 {
407 	ulong val;
408 
409 	_chanop(c, CHANRCV, &val, 0);
410 	return val;
411 }
412