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;
}