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channel.c
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channel.c
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/* Copyright (c) 2005 Russ Cox, MIT; see COPYRIGHT */
#include "taskimpl.h"
Channel*
chancreate(int elemsize, int bufsize)
{
Channel *c;
c = malloc(sizeof *c+bufsize*elemsize);
if(c == nil){
fprint(2, "chancreate malloc: %r");
exit(1);
}
memset(c, 0, sizeof *c);
c->elemsize = elemsize;
c->bufsize = bufsize;
c->nbuf = 0;//当前存了多少个
c->buf = (uchar*)(c+1);
return c;
}
/* bug - work out races */
void
chanfree(Channel *c)
{
if(c == nil)
return;
free(c->name);
free(c->arecv.a);
free(c->asend.a);
free(c);
}
static void
addarray(Altarray *a, Alt *alt)
{
if(a->n == a->m){
a->m += 16;
a->a = realloc(a->a, a->m*sizeof a->a[0]);
}
a->a[a->n++] = alt;
}
static void
delarray(Altarray *a, int i)
{
--a->n;
a->a[i] = a->a[a->n];
}
/*
* doesn't really work for things other than CHANSND and CHANRCV
* but is only used as arg to chanarray, which can handle it
*/
//算一下当前这个op上面还缺少的OP
#define otherop(op) (CHANSND+CHANRCV-(op))
static Altarray*
chanarray(Channel *c, uint op)
{//得到指定OP的数组
switch(op){
default:
return nil;
case CHANSND:
return &c->asend;
case CHANRCV:
return &c->arecv;
}
}
static int
altcanexec(Alt *a)
{
Altarray *ar;
Channel *c;
if(a->op == CHANNOP)
return 0;
c = a->c;
if(c->bufsize == 0){//整形数的时候,为0
ar = chanarray(c, otherop(a->op));//为啥要用otherop,其实就是去掉设置的OP,用没有设置的那个
//比如我这是发送, 那么这里得到的ar等于&c->arecv 接收数组
return ar && ar->n;//数组不为空,并且还有元素
}else{
switch(a->op){
default:
return 0;
case CHANSND://如果还有空间可以存,那么久返回可以执行
return c->nbuf < c->bufsize;
case CHANRCV://想读,并且内存里面还有,那么返回可以执行
return c->nbuf > 0;
}
}
}
static void
altqueue(Alt *a)
{
Altarray *ar;
ar = chanarray(a->c, a->op);
addarray(ar, a);
}
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 void
altalldequeue(Alt *a)
{
int i;
for(i=0; a[i].op!=CHANEND && a[i].op!=CHANNOBLK; i++)
if(a[i].op != CHANNOP)
altdequeue(&a[i]);
}
static void
amove(void *dst, void *src, uint n)
{
if(dst){
if(src == nil)
memset(dst, 0, n);
else
memmove(dst, src, n);
}
}
/*
* Actually move the data around. There are up to three
* players: the sender, the receiver, and the channel itself.
* If the channel is unbuffered or the buffer is empty,
* data goes from sender to receiver. If the channel is full,
* the receiver removes some from the channel and the sender
* gets to put some in.
*/
static void
altcopy(Alt *s, Alt *r)
{
Alt *t;
Channel *c;
uchar *cp;
/*
* Work out who is sender and who is receiver
*/
if(s == nil && r == nil)
return;
assert(s != nil);
c = s->c;
if(s->op == CHANRCV){
t = s;
s = r;
r = t;
}
assert(s==nil || s->op == CHANSND);
assert(r==nil || r->op == CHANRCV);
/*
* Channel is empty (or unbuffered) - copy directly.
*/
if(s && r && c->nbuf == 0){
amove(r->v, s->v, c->elemsize);
return;
}
/*
* Otherwise it's always okay to receive and then send.
*/
if(r){
cp = c->buf + c->off*c->elemsize;
amove(r->v, cp, c->elemsize);
--c->nbuf;
if(++c->off == c->bufsize)
c->off = 0;
}
if(s){
cp = c->buf + (c->off+c->nbuf)%c->bufsize*c->elemsize;
amove(cp, s->v, c->elemsize);
++c->nbuf;
}
}
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;//又随机取一个位置
other = ar->a[i];
altcopy(a, other);
altalldequeue(other->xalt);
other->xalt[0].xalt = other;
taskready(other->task);
}else
altcopy(a, nil);
}
#define dbgalt 0
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;//前面有这么多个元素
canblock = a[i].op == CHANEND;//可以阻塞?
t = taskrunning;
for(i=0; i<n; i++){
a[i].task = t;//指向发送的协程
a[i].xalt = a;
}
ncan = 0;
for(i=0; i<n; i++){//遍历每一个消息
c = a[i].c;//所指的协程
if(altcanexec(&a[i])){//查看该操作是否可以执行
ncan++;
}
}
if(ncan){
j = rand()%ncan;
for(i=0; i<n; i++){
if(altcanexec(&a[i])){
if(j-- == 0){//随机找一个位置,从后往前放
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;
}
static int
_chanop(Channel *c, int op, void *p, int canblock)
{
Alt a[2];
a[0].c = c;
a[0].op = op;//放一个操作指令在这
a[0].v = p;
a[1].op = canblock ? CHANEND : CHANNOBLK;//结束
if(chanalt(a) < 0)
return -1;
return 1;
}
int
chansend(Channel *c, void *v)
{
return _chanop(c, CHANSND, v, 1);
}
int
channbsend(Channel *c, void *v)
{
return _chanop(c, CHANSND, v, 0);
}
int
chanrecv(Channel *c, void *v)
{
return _chanop(c, CHANRCV, v, 1);
}
int
channbrecv(Channel *c, void *v)
{
return _chanop(c, CHANRCV, v, 0);
}
int
chansendp(Channel *c, void *v)
{
return _chanop(c, CHANSND, (void*)&v, 1);
}
void*
chanrecvp(Channel *c)
{
void *v;
_chanop(c, CHANRCV, (void*)&v, 1);
return v;
}
int
channbsendp(Channel *c, void *v)
{
return _chanop(c, CHANSND, (void*)&v, 0);
}
void*
channbrecvp(Channel *c)
{
void *v;
_chanop(c, CHANRCV, (void*)&v, 0);
return v;
}
int
chansendul(Channel *c, ulong val)
{
return _chanop(c, CHANSND, &val, 1);
}
ulong
chanrecvul(Channel *c)
{
ulong val;
_chanop(c, CHANRCV, &val, 1);
return val;
}
int
channbsendul(Channel *c, ulong val)
{
return _chanop(c, CHANSND, &val, 0);
}
ulong
channbrecvul(Channel *c)
{
ulong val;
_chanop(c, CHANRCV, &val, 0);
return val;
}