currently, async log thread (the log flusher) doesn't quit at all.
It assumes that OS reclaims all resources like thread, semaphore.

when JVM is exiting, it's possible to observe
OSXSemaphore::wait() and OSXSemaphore::signal() fail with return value 15.
#define KERN_INVALID_NAME 15
/* The name doesn't denote a right in the task.

the crash sight looks like this:
Target 0: (java) stopped.
(lldb) bt
* thread #9, name = 'Java: AsyncLog Thread', stop reason = breakpoint 2.2
  * frame #0: 0x0000000102dcdf4f libjvm.dylib`report_vm_error(file="/Users/xxinliu/Devel/jdk/src/hotspot/os/bsd/semaphore_bsd.cpp", line=66, error_msg="assert(ret == 0) failed", detail_fmt="Failed to wait on semaphore") at debug.cpp:270:17
    frame #1: 0x000000010372e5b1 libjvm.dylib`OSXSemaphore::wait(this=0x0000000103e22800) at semaphore_bsd.cpp:66:3
    frame #2: 0x0000000102da1f3e libjvm.dylib`Semaphore::wait(this=0x0000000103e227f8) at semaphore.hpp:55:39
    frame #3: 0x000000010342346f libjvm.dylib`AsyncLogLocker::AsyncLogLocker(this=0x000070000d627eb0) at logAsyncWriter.cpp:39:11
    frame #4: 0x0000000103422395 libjvm.dylib`AsyncLogLocker::AsyncLogLocker(this=0x000070000d627eb0) at logAsyncWriter.cpp:38:20
    frame #5: 0x0000000103422aed libjvm.dylib`AsyncLogWriter::write(this=0x0000000100214dc0) at logAsyncWriter.cpp:128:20
    frame #6: 0x0000000103422eb9 libjvm.dylib`AsyncLogWriter::run(this=0x0000000100214dc0) at logAsyncWriter.cpp:159:5
    frame #7: 0x0000000103927bae libjvm.dylib`Thread::call_run(this=0x0000000100214dc0) at thread.cpp:394:9
    frame #8: 0x0000000103634af7 libjvm.dylib`thread_native_entry(thread=0x0000000100214dc0) at os_bsd.cpp:591:11
    frame #9: 0x00007fff6c27a109 libsystem_pthread.dylib`_pthread_start + 148
    frame #10: 0x00007fff6c275b8b libsystem_pthread.dylib`thread_start + 15


It's Main thread is exiting. all static variables are destroying. therefore, OSXSemaphore may have been destroyed.

* thread #2
  * frame #0: 0x00007fff31e03889 CoreDisplay`std::__1::unique_ptr<CoreDisplay::IOBacklightWrapper, std::__1::default_delete<CoreDisplay::IOBacklightWrapper> >::reset(CoreDisplay::IOBacklightWrapper*) + 9
    frame #1: 0x00007fff6c11f13c libsystem_c.dylib`__cxa_finalize_ranges + 319
    frame #2: 0x00007fff6c11f412 libsystem_c.dylib`exit + 55
    frame #3: 0x000000010011c871 libjli.dylib`apple_main(arg=0x00007ffeefbfe880) at java_md_macosx.m:309:5
    frame #4: 0x00007fff6c27a109 libsystem_pthread.dylib`_pthread_start + 148
    frame #5: 0x00007fff6c275b8b libsystem_pthread.dylib`thread_start + 15