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Re: Warning: Unstable POSIX threads support comitted to CVS

From: Mikael Djurfeldt
Subject: Re: Warning: Unstable POSIX threads support comitted to CVS
Date: Wed, 11 Dec 2002 08:21:17 +0100
User-agent: Gnus/5.090008 (Oort Gnus v0.08) Emacs/21.2 (i386-pc-linux-gnu)

Mikael Djurfeldt <address@hidden> writes:

> (par-fib 100 5) crashes for me... :)

It no longer does.  In fact, I can't make the POSIX threads support to
crash anylonger with my basic test programs.  :-)

The cause of the (par-fib 100 5) problem was interesting:

scm_make_root (SCM parent)
  SCM root;
  scm_root_state *root_state;

  root_state = (scm_root_state *) scm_gc_malloc (sizeof (scm_root_state),
                                                 "root state");
  if (SCM_ROOTP (parent))
      memcpy (root_state, SCM_ROOT_STATE (parent), sizeof (scm_root_state));
      [scm_copy_fluids mutates root_state with the new fluids:]
      scm_copy_fluids (root_state);
      root_state->parent = parent;

  [The following entry to a critical section is a point where GC can happen.
   Note how the new fluids are unprotected!]
  SCM_NEWSMOB (root, scm_tc16_root, root_state);
  root_state->handle = root;
  return root;

Actually, in this case, we no longer need a critical section.

Currently, GC can only happen:

1. When we allocate cells.

2. When we perform any operation which has the potential to block the
   process (like locking a mutex using scm_mutex_lock or doing I/O or
   entering a critical section.

Mikael D.

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