As documented in the bug report, the double checked locking
pattern has inherent issues, and cannot guarantee correct
initialization.
This patch replaces the logic in init_available_charsets()
with the use of pthread_once(3). A wrapper function,
my_pthread_once(), is introduced and is used in lieu of direct
calls to init_available_charsets(). Related defines
MY_PTHREAD_ONCE_* are also introduced.
For the Windows platform, the implementation in lp:sysbench is
ported. For single-thread use, a simple define calls the
function and sets the pthread_once control variable.
Charset initialization is modified to use my_pthread_once().
http://lists.mysql.com/commits/59686
Cleanup pthread_self(), pthread_create(), pthread_join() implementation on Windows.
Prior implementation is was unnecessarily complicated and even differs in embedded
and non-embedded case.
Improvements in this patch:
* pthread_t is now the unique thread ID, instead of HANDLE returned by beginthread
This simplifies pthread_self() to be just straight GetCurrentThreadId().
prior it was much art involved in passing the beginthread() handle from the caller
to the TLS structure in the child thread ( did not work for the main thread of
course)
* remove MySQL specific my_thread_init()/my_thread_end() from pthread_create.
No automagic is done on Unix on pthread_create(). Having the same on Windows will
improve portability and avoid extra #ifdef's
* remove redefinition of getpid() - it was defined as GetCurrentThreadId()
htttp://lists.mysql.com/commits/50957?f=plain
Always use TLS functions instead of __declspec(thread) to access
thread local storage variables.
The change removes the necessity to recomplile the same source
files twice - with USE_TLS for DLLs and without USE_TLS for EXEs.
Real benefit of this change is better readability and maintainability
of TLS functions within MySQL.
There is a performance loss using TlsXXX functions compared to __declspec
but the difference is negligible in practice. In a sysbench-like benchmark
I ran with with TlsGetValue, pthread_[get|set]_specific was called 600000000
times and took 0.17sec of total 35min CPU time, or 0.008%.
It's not possible to use WaitForSingleObject to wait
on a CRITICAL_SECTION, instead use the TryEnterCriticalSection function.
- if "mutex" was already taken => return EBUSY
- if "mutex" was aquired => return 0
