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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)
{
mux->tagrend.l = &mux->lk;
mux->sleep.next = &mux->sleep;
mux->sleep.prev = &mux->sleep;
}
void*
muxrpc(Mux *mux, void *tx)
{
uint tag;
Muxrpc *r, *r2;
void *p;
/* must malloc because stack could be private */
r = mallocz(sizeof(Muxrpc), 1);
if(r == nil)
return nil;
r->r.l = &mux->lk;
/* assign the tag */
tag = gettag(mux, r);
if(mux->settag(mux, tx, tag) < 0){
puttag(mux, r);
free(r);
return nil;
}
/* send the packet */
if(_muxsend(mux, tx) < 0){
puttag(mux, r);
free(r);
return nil;
}
/* add ourselves to sleep queue */
qlock(&mux->lk);
enqueue(mux, r);
/* wait for our packet */
while(mux->muxer && !r->p)
rsleep(&r->r);
/* if not done, there's no muxer: start muxing */
if(!r->p){
if(mux->muxer)
abort();
mux->muxer = 1;
while(!r->p){
qunlock(&mux->lk);
p = _muxrecv(mux);
if(p)
tag = mux->gettag(mux, p);
else
tag = ~0;
qlock(&mux->lk);
if(p == nil){ /* eof -- just give up and pass the buck */
dequeue(mux, r);
break;
}
/* 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! */
continue;
}
r2 = mux->wait[tag];
r2->p = p;
rwakeup(&r2->r);
}
mux->muxer = 0;
/* if there is anyone else sleeping, wake them to mux */
if(mux->sleep.next != &mux->sleep)
rwakeup(&mux->sleep.next->r);
}
p = r->p;
puttag(mux, r);
free(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;
Again:
while(mux->nwait == mux->mwait)
rsleep(&mux->tagrend);
i=mux->freetag;
if(mux->wait[i] == 0)
goto Found;
for(i=0; i<mux->mwait; i++)
if(mux->wait[i] == 0){
Found:
mux->nwait++;
mux->wait[i] = r;
r->tag = i;
return i;
}
fprint(2, "libfs: nwait botch\n");
goto Again;
}
static void
puttag(Mux *mux, Muxrpc *r)
{
assert(mux->wait[r->tag] == r);
mux->wait[r->tag] = nil;
mux->nwait--;
mux->freetag = r->tag;
rwakeup(&mux->tagrend);
}
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