#include <u.h>#include <libc.h>#include <thread.h>#include <9pclient.h>#include "acme.h" extern int debug; #define dprint if(debug>1)print typedef struct Waitreq Waitreq;struct Waitreq{	int pid;	Channel *c;}; /* * watch the exiting children */Channel *twaitchan;	/* chan(Waitreq) */voidwaitthread(void *v){	Alt a[3];	Waitmsg *w, **wq;	Waitreq *rq, r;	int i, nrq, nwq; 	threadsetname("waitthread");	a[0].c = threadwaitchan();	a[0].v = &w;	a[0].op = CHANRCV;	a[1].c = twaitchan;	a[1].v = &r;	a[1].op = CHANRCV;	a[2].op = CHANEND; 	nrq = 0;	nwq = 0;	rq = nil;	wq = nil;	dprint("wait: start\n");	for(;;){	cont2:;		dprint("wait: alt\n");		switch(alt(a)){		case 0:			dprint("wait: pid %d exited\n", w->pid);			for(i=0; i<nrq; i++){				if(rq[i].pid == w->pid){					dprint("wait: match with rq chan %p\n", rq[i].c);					sendp(rq[i].c, w);					rq[i] = rq[--nrq];					goto cont2;				}			}			if(i == nrq){				dprint("wait: queueing waitmsg\n");				wq = erealloc(wq, (nwq+1)*sizeof(wq[0]));				wq[nwq++] = w;			}			break;				case 1:			dprint("wait: req for pid %d chan %p\n", r.pid, r.c);			for(i=0; i<nwq; i++){				if(w->pid == r.pid){					dprint("wait: match with waitmsg\n");					sendp(r.c, w);					wq[i] = wq[--nwq];					goto cont2;				}			}			if(i == nwq){				dprint("wait: queueing req\n");				rq = erealloc(rq, (nrq+1)*sizeof(rq[0]));				rq[nrq] = r;				dprint("wait: queueing req pid %d chan %p\n", rq[nrq].pid, rq[nrq].c);				nrq++;			}			break;		}	}} Waitmsg*twaitfor(int pid){	Waitreq r;	Waitmsg *w;		r.pid = pid;	r.c = chancreate(sizeof(Waitmsg*), 1);	send(twaitchan, &r);	w = recvp(r.c);	chanfree(r.c);	return w;} inttwait(int pid){	int x;	Waitmsg *w;		w = twaitfor(pid);	x = w->msg[0] != 0 ? -1 : 0;	free(w);	return x;} voidtwaitinit(void){	threadwaitchan();	/* allocate it before returning */	twaitchan = chancreate(sizeof(Waitreq), 10);	threadcreate(waitthread, nil, 128*1024);}