/* 检查Alt a是否可以被执行
*/
static int
altcanexec(Alt *a)
{
Altarray *ar;
Channel *c;
if(a->op == CHANNOP)
return 0;
c = a->c;
if(c->bufsize == 0){ // 如果bufsize为0，则是通过发送接收队列共享数据的
// 获取发送or接收队列
ar = chanarray(c, otherop(a->op));
return ar && ar->n;
}else{
switch(a->op){
default:
return 0;
case CHANSND:
// 如果是发送的情况，查看buffer还有没有空间了
return c->nbuf < c->bufsize;
case CHANRCV:
// 如果是接收的情况，查看buffer还有没有数据
return c->nbuf > 0;
}
}
}
/*
a->op is Recv: 从对应得Channel的发送队列随机取出一个Alt，
并读取数据，Alt对应的Task可以进入就绪队列了
a->op is Send: 将数据拷贝到Buffer中
*/
static void
altexec(Alt *a)
{
int i;
Altarray *ar;
Alt *other;
Channel *c;
c = a->c;
ar = chanarray(c, otherop(a->op));
if(ar && ar->n){
// 这里的逻辑目前看都是a->op == RECV才跑得到
i = rand()%ar->n;
other = ar->a[i];
// a->v = other->v
altcopy(a, other);
// 将other从Channel的队列（接收队列）中删除
altalldequeue(other->xalt);
other->xalt[0].xalt = other;
// Task重新进入就绪队列
taskready(other->task);
}else {
// 将a->v的数据放到buffer里面
altcopy(a, nil);
}
}
static void
altqueue(Alt *a)
{
Altarray *ar;
ar = chanarray(a->c, a->op);
addarray(ar, a);
}
static void
altexec(Alt *a)
{
int i;
Altarray *ar;
Alt *other;
Channel *c;
c = a->c;
ar = chanarray(c, otherop(a->op));
if(ar && ar->n){
i = rand()%ar->n;
other = ar->a[i];
altcopy(a, other);
altalldequeue(other->xalt);
other->xalt[0].xalt = other;
taskready(other->task);
}else
altcopy(a, nil);
}
static void
altdequeue(Alt *a)
{
int i;
Altarray *ar;
ar = chanarray(a->c, a->op);
if(ar == nil){
fprint(2, "bad use of altdequeue op=%d\n", a->op);
abort();
}
for(i=0; i<ar->n; i++)
if(ar->a[i] == a){
delarray(ar, i);
return;
}
fprint(2, "cannot find self in altdq\n");
abort();
}
static int
altcanexec(Alt *a)
{
Altarray *ar;
Channel *c;
if(a->op == CHANNOP)
return 0;
c = a->c;
if(c->bufsize == 0){
ar = chanarray(c, otherop(a->op));
return ar && ar->n;
}else{
switch(a->op){
default:
return 0;
case CHANSND:
return c->nbuf < c->bufsize;
case CHANRCV:
return c->nbuf > 0;
}
}
}