Re: Number of threads per process

From: Casper H.S. Dik (Casper.Dik_at_Sun.COM)
Date: 01/06/04 

Date: 06 Jan 2004 13:59:53 GMT

Gavin Maltby <G_a_v_i_n.M_a_l_t_b_y@sun.com> writes:

>I don't think a file descriptor is used per thread created (I'd
>be very surprised). To create the stack for the new thread
>(if not preconstructed) some anon memory is mapped, and
>(at least in the old libthread) that involves opening
>/dev/zero (it wasn't held open). So if you run out of
>file descriptors you can not be able to create threads
>(since the open of /dev/zero can fail; not sure
>how things are done in the newer libthread).

MAP_ANON is used to allocate thread stacks starting with Solaris 8 when
MAP_ANON was introduced in Solaris. Since that moment file descriptors
are not involved in creating threads.

Prior to that a cached fd to /dev/zero was used.

>The main limit on the number of threads you can create is
>VM space, for a 32-bit application anyway. Only so many
>stacks can fit in 32-bits, and each stack normally has
>a further 8K guardpage (unmapped, but takes VM space).
>When you hit this limit depends on the the stack size
>being requested each time. Again a truss will let you
>observe this.

I think that on UltraSPARC system the alignment is always on 64K
boundaries.

Casper 

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