This is the first release that passes the test suite for multiple Windows configurations, thanks in large part to @glandium setting up continuous integration via AppVeyor (and Travis CI for Linux and OS X).

New features:

• Add "J" (JSON) support to malloc_stats_print(). (@jasone)
• Add Cray compiler support. (@ronawho)

Optimizations:

• Add/use adaptive spinning for bootstrapping and radix tree node initialization. (@jasone)

Bug fixes:

• Fix large allocation to search starting in the optimal size class heap, which can substantially reduce virtual memory churn and fragmentation. This regression was first released in 4.0.0. (@mjp41, @jasone)
• Fix stats.arenas.<i>.nthreads accounting. (@interwq)
• Fix and simplify decay-based purging. (@jasone)
• Make DSS (sbrk(2)-related) operations lockless, which resolves potential deadlocks during thread exit. (@jasone)
• Fix over-sized allocation of radix tree leaf nodes. (@mjp41, @ogaun, @jasone)
• Fix over-sized allocation of arena_t (plus associated stats) data structures. (@jasone, @interwq)
• Fix EXTRA_CFLAGS to not affect configuration. (@jasone)
• Fix a Valgrind integration bug. (@ronawho)
• Disallow 0x5a junk filling when running in Valgrind. (@jasone)
• Fix a file descriptor leak on Linux. This regression was first released in 4.2.0. (@vsarunas, @jasone)
• Fix static linking of jemalloc with glibc. (@djwatson)
• Use syscall(2) rather than {open,read,close}(2) during boot on Linux. This works around other libraries' system call wrappers performing reentrant allocation. (@kspinka, @Whissi, @jasone)
• Fix OS X default zone replacement to work with OS X 10.12. (@glandium, @jasone)
• Fix cached memory management to avoid needless commit/decommit operations during purging, which resolves permanent virtual memory map fragmentation issues on Windows. (@mjp41, @jasone)
• Fix TSD fetches to avoid (recursive) allocation. This is relevant to non-TLS and Windows configurations. (@jasone)
• Fix malloc_conf overriding to work on Windows. (@jasone)
• Forcibly disable lazy-lock on Windows (was forcibly enabled). (@jasone)