Core: fixed a race resulting in extra sem_post()'s. The mtx->wait counter was not decremented if we were able to obtain the lock right after incrementing it. This resulted in unneeded sem_post() calls, eventually leading to EOVERFLOW errors being logged, "sem_post() failed while wake shmtx (75: Value too large for defined data type)". To close the race, mtx->wait is now decremented if we obtain the lock right after incrementing it in ngx_shmtx_lock(). The result can become -1 if a concurrent ngx_shmtx_unlock() decrements mtx->wait before the added code does. However, that only leads to one extra iteration in the next call of ngx_shmtx_lock().

ngx_addon_name=ngx_mysql

HTTP_MODULES="$HTTP_MODULES ngx_http_mysql_test_module"

HTTP_INCS="$HTTP_INCS $ngx_addon_dir"
HTTP_DEPS="$HTTP_DEPS $ngx_addon_dir/ngx_mysql.h"
#CORE_LIBS="$CORE_LIBS -lmd"

USE_SHA1=YES

NGX_ADDON_SRCS="$NGX_ADDON_SRCS $ngx_addon_dir/ngx_mysql.c"
NGX_ADDON_SRCS="$NGX_ADDON_SRCS $ngx_addon_dir/ngx_http_mysql_test.c"