int
chanalt(Alt *a)
{
int i, j, ncan, n, canblock;
Channel *c;
Task *t;
needstack(512);
for(i=0; a[i].op != CHANEND && a[i].op != CHANNOBLK; i++)
;
n = i;
canblock = a[i].op == CHANEND;
t = taskrunning;
//所有alt指向正在运行的task
for(i=0; i<n; i++){
a[i].task = t;
a[i].xalt = a;
}
ncan = 0;
for(i=0; i<n; i++){
if(altcanexec(&a[i])){
ncan++;
}
}
if(ncan){
j = rand()%ncan;
for(i=0; i<n; i++){
if(altcanexec(&a[i])){
if(j-- == 0){
altexec(&a[i]);
return i;
}
}
}
}
if(!canblock)
return -1;
for(i=0; i<n; i++){
if(a[i].op != CHANNOP)
altqueue(&a[i]);
}
taskswitch();
/*
* the guy who ran the op took care of dequeueing us
* and then set a[0].alt to the one that was executed.
*/
return a[0].xalt - a;
}
int
chanalt(Alt *a)
{
int i, j, ncan, n, canblock;
Channel *c;
Task *t;
needstack(512);
for(i=0; a[i].op != CHANEND && a[i].op != CHANNOBLK; i++)
;
n = i;
canblock = a[i].op == CHANEND;
t = taskrunning;
for(i=0; i<n; i++){
a[i].task = t;
a[i].xalt = a;
}
if(dbgalt) print("alt ");
ncan = 0;
for(i=0; i<n; i++){
c = a[i].c;
if(dbgalt) print(" %c:", "esrnb"[a[i].op]);
if(dbgalt) { if(c->name) print("%s", c->name); else print("%p", c); }
if(altcanexec(&a[i])){
if(dbgalt) print("*");
ncan++;
}
}
if(ncan){
j = rand()%ncan;
for(i=0; i<n; i++){
if(altcanexec(&a[i])){
if(j-- == 0){
if(dbgalt){
c = a[i].c;
print(" => %c:", "esrnb"[a[i].op]);
if(c->name) print("%s", c->name); else print("%p", c);
print("\n");
}
altexec(&a[i]);
return i;
}
}
}
}
if(dbgalt)print("\n");
if(!canblock)
return -1;
for(i=0; i<n; i++){
if(a[i].op != CHANNOP)
altqueue(&a[i]);
}
taskswitch();
/*
* the guy who ran the op took care of dequeueing us
* and then set a[0].alt to the one that was executed.
*/
return a[0].xalt - a;
}
int
alt(Alt *alts)
{
Alt *a, *xa, *ca;
Channel volatile *c;
int n, s, waiting, allreadycl;
void* r;
Thread *t;
/*
* The point of going splhi here is that note handlers
* might reasonably want to use channel operations,
* but that will hang if the note comes while we hold the
* chanlock. Instead, we delay the note until we've dropped
* the lock.
*/
t = _threadgetproc()->thread;
if(t->moribund || _threadexitsallstatus)
yield(); /* won't return */
s = _procsplhi();
lock(&chanlock);
t->alt = alts;
t->chan = Chanalt;
/* test whether any channels can proceed */
n = 0;
a = nil;
for(xa=alts; xa->op!=CHANEND && xa->op!=CHANNOBLK; xa++){
xa->entryno = -1;
if(xa->op == CHANNOP)
continue;
c = xa->c;
if(c==nil){
unlock(&chanlock);
_procsplx(s);
t->chan = Channone;
return -1;
}
if(isopenfor(c, xa->op) && canexec(xa))
if(nrand(++n) == 0)
a = xa;
}
if(a==nil){
/* nothing can proceed */
if(xa->op == CHANNOBLK){
unlock(&chanlock);
_procsplx(s);
t->chan = Channone;
if(xa->op == CHANNOBLK)
return xa - alts;
}
/* enqueue on all channels open for us. */
c = nil;
ca = nil;
waiting = 0;
allreadycl = 0;
for(xa=alts; xa->op!=CHANEND; xa++)
if(xa->op==CHANNOP)
continue;
else if(isopenfor(xa->c, xa->op)){
waiting = 1;
enqueue(xa, &c);
} else if(xa->err != errcl)
ca = xa;
else
allreadycl = 1;
if(waiting == 0)
if(ca != nil){
/* everything was closed, select last channel */
ca->err = errcl;
unlock(&chanlock);
_procsplx(s);
t->chan = Channone;
return ca - alts;
} else if(allreadycl){
/* everything was already closed */
unlock(&chanlock);
_procsplx(s);
t->chan = Channone;
return -1;
}
/*
* wait for successful rendezvous.
* we can't just give up if the rendezvous
* is interrupted -- someone else might come
* along and try to rendezvous with us, so
* we need to be here.
* if the channel was closed, the op is done
* and we flag an error for the entry.
*/
Again:
unlock(&chanlock);
_procsplx(s);
r = _threadrendezvous(&c, 0);
s = _procsplhi();
lock(&chanlock);
if(r==Intred){ /* interrupted */
if(c!=nil) /* someone will meet us; go back */
goto Again;
c = (Channel*)~0; /* so no one tries to meet us */
}
/* dequeue from channels, find selected one */
a = nil;
for(xa=alts; xa->op!=CHANEND; xa++){
if(xa->op==CHANNOP)
continue;
if(xa->c == c){
a = xa;
a->err = nil;
if(r == Closed)
a->err = errcl;
}
dequeue(xa);
}
unlock(&chanlock);
_procsplx(s);
if(a == nil){ /* we were interrupted */
assert(c==(Channel*)~0);
return -1;
}
}else
altexec(a, s); /* unlocks chanlock, does splx */
_sched();
t->chan = Channone;
return a - alts;
}