求教，线程同步问题？

struct server_context
{
CRITICAL_SECTION cs;
int running;
};主线程：
...
struct server_context *sc = (struct server_context *)param;while(sc->running)
{
//accept connection and handle.
}
...工作线程：
...
struct server_context *sc = (struct server_context *)param;EnterCriticalSection(&sc->cs);
sc->running = 0;
LeaveCriticalSection(&sc->cs);
...运行工作线程后，主线程并没有因为sc->runnning = 0而退出循环，请教各位大侠，是何缘由。