Jerome Vouillon wrote:

> You should try to run your program with the strace program, which
> traces system calls.  This will tell you why your program runs
> continuously rather than waiting for I/Os.

Okay, I've done the strace. I found something that appears to be 
significant, but I don't really understand it. After the GUI is 
displayed, there are a number of GTK library calls, and then some 
searches for various resources--locale files, fonts, icons--and then this:

poll([{fd=3, events=POLLIN}], 1, 0)     = 0
write(3, "\1\30\r\0\3\0\340\0D\0\0\0\0\0\0\0\251\0\244\1\0\0\1\0"..., 
2132) = 2132
ioctl(3, FIONREAD, [1184])              = 0
read(3, "\34\317N\0\3\0\340\0\31\1\0\0\376\331]E\0\330]Ex\202\37"..., 
1184) = 1184
poll([{fd=3, events=POLLIN}], 1, 0)     = 0
poll([{fd=3, events=POLLIN}], 1, 0)     = 0
poll([{fd=3, events=POLLIN}], 1, 0)     = 0
poll([{fd=3, events=POLLIN}], 1, 0)     = 0
poll([{fd=3, events=POLLIN}], 1, 0)     = 0
poll([{fd=3, events=POLLIN}], 1, 0)     = 0
poll([{fd=3, events=POLLIN}], 1, 0)     = 0
poll([{fd=3, events=POLLIN}], 1, 0)     = 0
poll([{fd=3, events=POLLIN}], 1, 0)     = 0
ioctl(3, FIONREAD, [0])                 = 0
poll([{fd=3, events=POLLIN}], 1, 0)     = 0
ioctl(3, FIONREAD, [0])                 = 0
poll([{fd=3, events=POLLIN}], 1, 0)     = 0
write(3, "5\30\4\0&\0\340\0\36\0\340\0\245\0\20\0\230\4\5\0\'\0\340"..., 
13780) = 13780
ioctl(3, FIONREAD, [0])                 = 0
poll([{fd=3, events=POLLIN}], 1, 0)     = 0
ioctl(3, FIONREAD, [0])                 = 0
poll([{fd=3, events=POLLIN}, {fd=7, events=POLLIN, revents=POLLHUP}], 2, 
-1) = 1

The last two lines are then repeated around 18000 times (identically 
each time, as far as I can see), until the 'quit' command is received. 
This takes place over a span of perhaps 30 seconds of real time. So 
pretty clearly this is the CPU-eating behavior, but I still can't see 
what is triggering it. By the way, FD #7 is my FIFO.

Well, based on the above, I tried adding a second watch function:

   let hup_watcher _ = Util.sleep 0.25; true in
   (* ... unrelated code omitted ... *)
   ignore (GMain.Io.add_watch ~cond:[`HUP] ~callback:hup_watcher chan)

Finally, this produces a change in behavior--but not quite what I need. 
CPU usage is under control, but now the GUI fails to display completely: 
the main window appears, with the outine of the TreeView widget it is 
supposed to have, but the contents are never displayed.

-- 
Matt Gushee
: Bantam - lightweight file manager : matt.gushee.net/software/bantam/ :
: RASCL's A Simple Configuration Language :     matt.gushee.net/rascl/ :