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libdraw: avoid deadlock for mouse ioproc sending on resizec 

a deadlock has been observed with samterm (thanks burnzez),
that shows the mouse ioproc being stuck in sending on the
resize channel, while the mouse consumer is stuck in a
readmouse() loop wanting a rectangle to be drawn by the
user:

recv(v=0x42df50)+0x28 /sys/src/libthread/channel.c:321
readmouse(mc=0x42df50)+0x54 /sys/src/libdraw/mouse.c:34
getrect(.ret=0x41bce0,but=0x4,mc=0x42df50)+0x62 /sys/src/libdraw/getrect.c:49
	r=0x41bc70
	rc=0x41bc70
getr(rp=0x41bce0)+0x24 /sys/src/cmd/samterm/main.c:244
	p=0x6b000004f6
	r=0x2
sweeptext(new=0x0,tag=0x2d)+0x12 /sys/src/cmd/samterm/menu.c:208
	r=0x2
	t=0x42df50
inmesg(type=0x2,count=0x2)+0x1ab /sys/src/cmd/samterm/mesg.c:136
	m=0x10000002d
	l=0x2d00001b00
	i=0x43829000000001
	t=0x438290
	lp=0x42e050
rcv()+0x7a /sys/src/cmd/samterm/mesg.c:77
threadmain(argv=0x7ffffeffef90)+0x173 /sys/src/cmd/samterm/main.c:63

so avoid blocking in the mouse ioproc by using nbsend()
instead of send() for writing to the resize channel.
front
cinap_lenrek 2018-11-18 03:37:04 +01:00
parent a25418fddc
commit 064ea89caa
1 changed files with 2 additions and 2 deletions
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4
sys/src/libdraw/mouse.c
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@ -66,7 +66,7 @@ _ioproc(void *arg)
switch(buf[0]){
case 'r':
one = 1;
if(send(mc->resizec, &one) < 0)
if(nbsend(mc->resizec, &one) < 0)
continue;
/* fall through */
case 'm':
@ -122,7 +122,7 @@ initmouse(char *file, Image *i)
free(t);
mc->image = i;
mc->c = chancreate(sizeof(Mouse), 0);
mc->resizec = chancreate(sizeof(int), 2);
mc->resizec = chancreate(sizeof(int), 1);
mc->pid = proccreate(_ioproc, mc, 4096);
return mc;
}