atomic check and update of shm flag

[Mathias Koerber]

Can I safely assume, that a contruct like

	while (shm_addr->flag == 0)
		;
	shm_addr->flag = getpid();

ensures that only one of several equal processes at a time
have access to a resource? I fear that one process finds the
flag set to zero, but is running out of time-slice, before it can set the
flag, and then another process also finds the flag set to zero and
uses the resource. If the above example doesn't work, what works?

I'd like to have a solution with shm, since I don't want to add even
another IPC-system (semaphores etc) only for this to work.

Please e-mail, address as in my (.sig).

Thx, Mathias
-- 
Mathias Koerber           |Tel:   +65 / 7473828 ext 1852|Fax: +65 / 7474331
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