jemalloc 4.0.1 released

[Jason Evans]

jemalloc 4.0.1 is now available.  This is a bugfix release that is somewhat high risk due to the amount of refactoring required to address deep xallocx() problems. As a side effect of these fixes, xallocx() now tries harder to partially fulfill requests for optional extra space. Note that a couple of minor heap profiling optimizations are included, but these are better thought of as performance fixes that were integral to disovering most of the other bugs.

Optimizations:
- Avoid a chunk metadata read in arena_prof_tctx_set(), since it is in the fast path when heap profiling is enabled. Additionally, split a special case out into arena_prof_tctx_reset(), which also avoids chunk metadata reads.
- Optimize irallocx_prof() to optimistically update the sampler state. The prior implementation appears to have been a holdover from when rallocx()/xallocx() functionality was combined as rallocm().

Bug fixes:
- Fix TLS configuration such that it is enabled by default for platforms on which it works correctly.
- Fix arenas_cache_cleanup() and arena_get_hard() to handle allocation/deallocation within the application's thread-specific data cleanup functions even after arenas_cache is torn down.
- Fix xallocx() bugs related to size+extra exceeding HUGE_MAXCLASS.
- Fix chunk purge hook calls for in-place huge shrinking reallocation to specify the old chunk size rather than the new chunk size. This bug caused no correctness issues for the default chunk purge function, but was visible to custom functions set via the "arena.<i>.chunk_hooks" mallctl.
- Fix heap profiling bugs:
  + Fix heap profiling to distinguish among otherwise identical sample sites with interposed resets (triggered via the "prof.reset" mallctl). This bug could cause data structure corruption that would most likely result in a segfault.
  + Fix irealloc_prof() to prof_alloc_rollback() on OOM.
  + Make one call to prof_active_get_unlocked() per allocation event, and use the result throughout the relevant functions that handle an allocation event. Also add a missing check in prof_realloc(). These fixes protect allocation events against concurrent prof_active changes.
  + Fix ixallocx_prof() to pass usize_max and zero to ixallocx_prof_sample() in the correct order.
  + Fix prof_realloc() to call prof_free_sampled_object() after calling prof_malloc_sample_object(). Prior to this fix, if tctx and old_tctx were the same, the tctx could have been prematurely destroyed.
- Fix portability bugs:
  + Don't bitshift by negative amounts when encoding/decoding run sizes in chunk header maps. This affected systems with page sizes greater than 8 KiB.
  + Rename index_t to szind_t to avoid an existing type on Solaris.
  + Add JEMALLOC_CXX_THROW to the memalign() function prototype, in order to match glibc and avoid compilation errors when including both jemalloc/jemalloc.h and malloc.h in C++ code.
  + Don't assume that /bin/sh is appropriate when running size_classes.sh during configuration.
  + Consider __sparcv9 a synonym for __sparc64__ when defining LG_QUANTUM.
  + Link tests to librt if it contains clock_gettime(2).

For the complete ChangeLog, see:
	https://github.com/jemalloc/jemalloc/raw/4.0.1/ChangeLog

Direct download:
	https://github.com/jemalloc/jemalloc/releases/download/4.0.1/jemalloc-4.0.1.tar.bz2

Starting point for general information:
	http://www.canonware.com/jemalloc/

Browsable revision history:
	https://github.com/jemalloc/jemalloc/tree/4.0.1