[Caml-list] signal-unsafety of %!

[Matej Kosik <5764c029b688c1c0d24a2e97cd764f@gmail.com>]

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Hi,

When I compile the attached program

  (with compilers available directly from Debian's repositories)

I can observe a (non-deterministic) deadlock.

When I remove

	%!

from the printf function inside the SIGALRM's handler, the deadlock never seem to occur.

Obviously, interference can be easily introduced in concurrent programs; I was just surprised that even something like

	%!

can cause it.

Isn't this something, that could be avoided in this case?

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open Unix

;;

Sys.set_signal Sys.sigalrm
               (Sys.Signal_handle (fun _ -> Printf.printf "H%!"));
ignore (Unix.alarm 1);
while true do
  Printf.printf ".%!"
done

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main : % : %.ml
	ocamlfind c -linkpkg -package unix $< -o $@

clean :
	rm -f *.cmo *.cmi main