re PR libstdc++/24469 (Possible race condition in mt_allocator causing SIGSEGV)

2006-09-02  Paolo Carlini  <pcarlini@suse.de>
	    Richard Guenther  <rguenther@suse.de>

	PR libstdc++/24469
	* src/mt_allocator.cc (__pool<true>::_M_reserve_block,
	__pool<true>::_M_reclaim_block): Fix the logic to avoid
	races, exploit atomic counters stored in second part of
	the memory pointed by _M_used.
	(__pool<true>::_M_initialize): Adjust _M_used allocation.
	* include/ext/mt_allocator.h (__pool<true>::_Bin_record):
	Update comment.

Co-Authored-By: Richard Guenther <rguenther@suse.de>

From-SVN: r116660

1 files changed, 7 insertions, 2 deletions

diff --git a/libstdc++-v3/include/ext/mt_allocator.h b/libstdc++-v3/include/ext/mt_allocator.h
index ae20d16..2379d82 100644
--- a/libstdc++-v3/include/ext/mt_allocator.h
+++ b/libstdc++-v3/include/ext/mt_allocator.h
@@ -298,8 +298,13 @@ _GLIBCXX_BEGIN_NAMESPACE(__gnu_cxx)
 
 	// An "array" of counters used to keep track of the amount of
 	// blocks that are on the freelist/used for each thread id.
-	// Memory to these "arrays" is allocated in _S_initialize() for
-	// _S_max_threads + global pool 0.
+	// - Note that the second part of the allocated _M_used "array"
+	//   actually hosts (atomic) counters of reclaimed blocks:  in
+	//   _M_reserve_block and in _M_reclaim_block those numbers are
+	//   subtracted from the first ones to obtain the actual size
+	//   of the "working set" of the given thread.
+	// - Memory to these "arrays" is allocated in _S_initialize()
+	//   for _S_max_threads + global pool 0.
 	size_t*				_M_free;
 	size_t*			        _M_used;