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/* Copyright (C) 2003 Russ Cox, Massachusetts Institute of Technology */
/* See COPYRIGHT */
/*
* Generic RPC packet multiplexor. Inspired by but not derived from
* Plan 9 kernel. Originally developed as part of Tra, later used in
* libnventi, and then finally split out into a generic library.
*/
#include <u.h>
#include <libc.h>
#include <mux.h>
static int gettag(Mux*, Muxrpc*);
static void puttag(Mux*, Muxrpc*);
static void enqueue(Mux*, Muxrpc*);
static void dequeue(Mux*, Muxrpc*);
void
muxinit(Mux *mux)
{
memset(&mux->lk, 0, sizeof(Mux)-offsetof(Mux, lk));
mux->tagrend.l = &mux->lk;
mux->rpcfork.l = &mux->lk;
mux->sleep.next = &mux->sleep;
mux->sleep.prev = &mux->sleep;
}
static Muxrpc*
allocmuxrpc(Mux *mux)
{
Muxrpc *r;
/* must malloc because stack could be private */
r = mallocz(sizeof(Muxrpc), 1);
if(r == nil){
werrstr("mallocz: %r");
return nil;
}
r->mux = mux;
r->r.l = &mux->lk;
r->waiting = 1;
return r;
}
static int
tagmuxrpc(Muxrpc *r, void *tx)
{
int tag;
Mux *mux;
mux = r->mux;
/* assign the tag, add selves to response queue */
qlock(&mux->lk);
tag = gettag(mux, r);
/*print("gettag %p %d\n", r, tag); */
enqueue(mux, r);
qunlock(&mux->lk);
/* actually send the packet */
if(tag < 0 || mux->settag(mux, tx, tag) < 0 || _muxsend(mux, tx) < 0){
werrstr("settag/send tag %d: %r", tag);
fprint(2, "%r\n");
qlock(&mux->lk);
dequeue(mux, r);
puttag(mux, r);
qunlock(&mux->lk);
return -1;
}
return 0;
}
void
muxmsgandqlock(Mux *mux, void *p)
{
int tag;
Muxrpc *r2;
tag = mux->gettag(mux, p) - mux->mintag;
/*print("mux tag %d\n", tag); */
qlock(&mux->lk);
/* hand packet to correct sleeper */
if(tag < 0 || tag >= mux->mwait){
fprint(2, "%s: bad rpc tag %ux\n", argv0, tag);
/* must leak packet! don't know how to free it! */
return;
}
r2 = mux->wait[tag];
if(r2 == nil || r2->prev == nil){
fprint(2, "%s: bad rpc tag %ux (no one waiting on that tag)\n", argv0, tag);
/* must leak packet! don't know how to free it! */
return;
}
r2->p = p;
dequeue(mux, r2);
rwakeup(&r2->r);
}
void
electmuxer(Mux *mux)
{
/* if there is anyone else sleeping, wake them to mux */
if(mux->sleep.next != &mux->sleep){
mux->muxer = mux->sleep.next;
rwakeup(&mux->muxer->r);
}else
mux->muxer = nil;
}
void*
muxrpc(Mux *mux, void *tx)
{
int tag;
Muxrpc *r;
void *p;
if((r = allocmuxrpc(mux)) == nil)
return nil;
if((tag = tagmuxrpc(r, tx)) < 0)
return nil;
qlock(&mux->lk);
/* wait for our packet */
while(mux->muxer && mux->muxer != r && !r->p)
rsleep(&r->r);
/* if not done, there's no muxer: start muxing */
if(!r->p){
if(mux->muxer != nil && mux->muxer != r)
abort();
mux->muxer = r;
while(!r->p){
qunlock(&mux->lk);
p = _muxrecv(mux, 1);
if(p == nil){
/* eof -- just give up and pass the buck */
qlock(&mux->lk);
dequeue(mux, r);
break;
}
muxmsgandqlock(mux, p);
}
electmuxer(mux);
}
/*print("finished %p\n", r); */
p = r->p;
puttag(mux, r);
qunlock(&mux->lk);
if(p == nil)
werrstr("unexpected eof");
return p;
}
Muxrpc*
muxrpcstart(Mux *mux, void *tx)
{
int tag;
Muxrpc *r;
if((r = allocmuxrpc(mux)) == nil)
return nil;
if((tag = tagmuxrpc(r, tx)) < 0)
return nil;
return r;
}
void*
muxrpccanfinish(Muxrpc *r)
{
char *p;
Mux *mux;
mux = r->mux;
qlock(&mux->lk);
if(!r->p && !mux->muxer){
mux->muxer = r;
while(!r->p){
qunlock(&mux->lk);
p = _muxrecv(mux, 0);
if(p == nil){
qlock(&mux->lk);
break;
}
muxmsgandqlock(mux, p);
}
electmuxer(mux);
}
p = r->p;
if(p)
puttag(mux, r);
qunlock(&mux->lk);
return p;
}
static void
enqueue(Mux *mux, Muxrpc *r)
{
r->next = mux->sleep.next;
r->prev = &mux->sleep;
r->next->prev = r;
r->prev->next = r;
}
static void
dequeue(Mux *mux, Muxrpc *r)
{
r->next->prev = r->prev;
r->prev->next = r->next;
r->prev = nil;
r->next = nil;
}
static int
gettag(Mux *mux, Muxrpc *r)
{
int i, mw;
Muxrpc **w;
for(;;){
/* wait for a free tag */
while(mux->nwait == mux->mwait){
if(mux->mwait < mux->maxtag-mux->mintag){
mw = mux->mwait;
if(mw == 0)
mw = 1;
else
mw <<= 1;
w = realloc(mux->wait, mw*sizeof(w[0]));
if(w == nil)
return -1;
memset(w+mux->mwait, 0, (mw-mux->mwait)*sizeof(w[0]));
mux->wait = w;
mux->freetag = mux->mwait;
mux->mwait = mw;
break;
}
rsleep(&mux->tagrend);
}
i=mux->freetag;
if(mux->wait[i] == 0)
goto Found;
for(; i<mux->mwait; i++)
if(mux->wait[i] == 0)
goto Found;
for(i=0; i<mux->freetag; i++)
if(mux->wait[i] == 0)
goto Found;
/* should not fall out of while without free tag */
fprint(2, "libfs: nwait botch\n");
abort();
}
Found:
mux->nwait++;
mux->wait[i] = r;
r->tag = i+mux->mintag;
return r->tag;
}
static void
puttag(Mux *mux, Muxrpc *r)
{
int i;
i = r->tag - mux->mintag;
assert(mux->wait[i] == r);
mux->wait[i] = nil;
mux->nwait--;
mux->freetag = i;
rwakeup(&mux->tagrend);
free(r);
}
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