+
+ int shm= XShmQueryExtension(disp);
+ debugf("PAGING shm=%d\n",shm);
+ if (shm) {
+ xassert( shmim= XShmCreateImage(disp, attr.visual, attr.depth, ZPixmap,
+ 0,&shminfo, wwidth,wheight) );
+
+ sigset_t oldset, all;
+ sigfillset(&all);
+ sysassert(! sigprocmask(SIG_BLOCK,&all,&oldset) );
+
+ int pfd[2];
+ pid_t cleaner;
+ sysassert(! pipe(pfd) );
+ sysassert( (cleaner= fork()) != -1 );
+ if (!cleaner) {
+ sysassert(! close(pfd[1]) );
+ for (;;) {
+ int r= read(pfd[0], &shminfo.shmid, sizeof(shminfo.shmid));
+ if (!r) exit(0);
+ if (r==sizeof(shminfo.shmid)) break;
+ assert(r==-1 && errno==EINTR);
+ }
+ for (;;) {
+ char bc;
+ int r= read(pfd[0],&bc,1);
+ if (r>=0) break;
+ assert(r==-1 && errno==EINTR);
+ }
+ sysassert(! shmctl(shminfo.shmid,IPC_RMID,0) );
+ exit(0);
+ }
+ sysassert(! close(pfd[0]) );
+
+ sysassert(! sigprocmask(SIG_SETMASK,&oldset,0) );
+
+ assert(shmim->height == wheight);
+ sysassert( (shminfo.shmid=
+ shmget(IPC_PRIVATE, shmim->bytes_per_line * wheight,
+ IPC_CREAT|0600)) >= 0 );
+
+ sysassert( write(pfd[1],&shminfo.shmid,sizeof(shminfo.shmid)) ==
+ sizeof(shminfo.shmid) );
+ sysassert( shminfo.shmaddr= shmat(shminfo.shmid,0,0) );
+ shmim->data= shminfo.shmaddr;
+ shminfo.readOnly= False;
+ xassert( XShmAttach(disp,&shminfo) );
+
+ close(pfd[1]); /* causes IPC_RMID */
+ }