windows lua 多线程 线程同步

今天在改一个程序，改成部分逻辑用lua写，这个程序是多线程的。将程序中部分逻辑改成lua之后，各种非法访问内存错误，各种奇奇怪怪的问题，不分时间，不分地点的出现崩溃。从调用堆栈来看，基本都是使用lua造成的。在多线程中使用lua_newthread得到的lus_State仍然有时候程序会崩溃。基本上可以确定为多线程中操作lua 的问题了。

前几天我转载的一篇文章，文章写了关于lua多线程的作法。作法有二

1.每一个线程函数用lua_newthread产生一个新的lua_state 以后对lua操作都用这个lua_state

2.修改lua源码使之成为支持多线程的（修改lua 源代码中lua_lock lua_unlock宏）

对于第2条，那篇文中的例子是用 pthread_mutex_t 来进行线程同步的pthread_mutex_t，我对pthread_mutex_t 不熟，网上一查才知道一般是在linux下C语言进行线程同步用的，在windows下面一般多线程都用CRITICAL_SECTION，和内核对象来进行线程同步的。于是产生了这篇文章。

修改代码如下：

1.global_State加一个成员变量  m_cs

Code Snippet

1. typedef struct global_State {
2.   stringtable strt;  /* hash table for strings */
3.   lua_Alloc frealloc;  /* function to reallocate memory */
4.   void *ud;         /* auxiliary data to `frealloc' */
5.   lu_byte currentwhite;
6.   lu_byte gcstate;  /* state of garbage collector */
7.   int sweepstrgc;  /* position of sweep in `strt' */
8.   GCObject *rootgc;  /* list of all collectable objects */
9.   GCObject **sweepgc;  /* position of sweep in `rootgc' */
10.   GCObject *gray;  /* list of gray objects */
11.   GCObject *grayagain;  /* list of objects to be traversed atomically */
12.   GCObject *weak;  /* list of weak tables (to be cleared) */
13.   GCObject *tmudata;  /* last element of list of userdata to be GC */
14.   Mbuffer buff;  /* temporary buffer for string concatentation */
15.   lu_mem GCthreshold;
16.   lu_mem totalbytes;  /* number of bytes currently allocated */
17.   lu_mem estimate;  /* an estimate of number of bytes actually in use */
18.   lu_mem gcdept;  /* how much GC is `behind schedule' */
19.   int gcpause;  /* size of pause between successive GCs */
20.   int gcstepmul;  /* GC `granularity' */
21.   lua_CFunction panic;  /* to be called in unprotected errors */
22.   TValue l_registry;
23.   struct lua_State *mainthread;
24.   UpVal uvhead;  /* head of double-linked list of all open upvalues */
25.   struct Table *mt[NUM_TAGS];  /* metatables for basic types */
26.   TString *tmname[TM_N];  /* array with tag-method names */
27.   CRITICAL_SECTION m_cs; /*windows mutithread */
28. } global_State;

2.在lua_newstate加入初始化Critical_section的代码 InitializeCriticalSection(&g->m_cs);

Code Snippet

1. LUA_API lua_State *lua_newstate (lua_Alloc f, void *ud) {
2.   int i;
3.   lua_State *L;
4.   global_State *g;
5.   void *l = (*f)(ud, NULL, 0, state_size(LG));
6.   if (l == NULL) return NULL;
7.   L = tostate(l);
8.   g = &((LG *)L)->g;
9.   L->next = NULL;
10.   L->tt = LUA_TTHREAD;
11.   g->currentwhite = bit2mask(WHITE0BIT, FIXEDBIT);
12.   L->marked = luaC_white(g);
13.   set2bits(L->marked, FIXEDBIT, SFIXEDBIT);
14.   preinit_state(L, g);
15.   g->frealloc = f;
16.   g->ud = ud;
17.   g->mainthread = L;
18.   g->uvhead.u.l.prev = &g->uvhead;
19.   g->uvhead.u.l.next = &g->uvhead;
20.   g->GCthreshold = 0;  /* mark it as unfinished state */
21.   g->strt.size = 0;
22.   g->strt.nuse = 0;
23.   g->strt.hash = NULL;
24.   setnilvalue(registry(L));
25.   luaZ_initbuffer(L, &g->buff);
26.   g->panic = NULL;
27.   g->gcstate = GCSpause;
28.   g->rootgc = obj2gco(L);
29.   g->sweepstrgc = 0;
30.   g->sweepgc = &g->rootgc;
31.   g->gray = NULL;
32.   g->grayagain = NULL;
33.   g->weak = NULL;
34.   g->tmudata = NULL;
35.   g->totalbytes = sizeof(LG);
36.   g->gcpause = LUAI_GCPAUSE;
37.   g->gcstepmul = LUAI_GCMUL;
38.   g->gcdept = 0;
39.   InitializeCriticalSection(&g->m_cs);
40.   for (i=0; i<NUM_TAGS; i++) g->mt[i] = NULL;
41.   if (luaD_rawrunprotected(L, f_luaopen, NULL) != 0) {
42.     /* memory allocation error: free partial state */
43.     close_state(L);
44.     L = NULL;
45.   }
46.   else
47.     luai_userstateopen(L);
48.   return L;
49. }

3.在close_state 加入删除CriticalSection的代码 DeleteCriticalSection(&g->m_cs);

Code Snippet

1. static void close_state (lua_State *L) {
2.   global_State *g = G(L);
3.   luaF_close(L, L->stack);  /* close all upvalues for this thread */
4.   luaC_freeall(L);  /* collect all objects */
5.   lua_assert(g->rootgc == obj2gco(L));
6.   lua_assert(g->strt.nuse == 0);
7.   luaM_freearray(L, G(L)->strt.hash, G(L)->strt.size, TString *);
8.   luaZ_freebuffer(L, &g->buff);
9.   freestack(L, L);
10.   lua_assert(g->totalbytes == sizeof(LG));
11.   DeleteCriticalSection(&g->m_cs);
12.   (*g->frealloc)(g->ud, fromstate(L), state_size(LG), 0);
13. }

4.修改lua_lock和lua_unlock宏如下

Code Snippet

1. #ifndef lua_lock
2. #define lua_lock(L) EnterCriticalSection(&(G(L)->m_cs))
3. #define lua_unlock(L) LeaveCriticalSection(&(G(L)->m_cs))
4. #endif

5.为了使用CRITICAL_SECTION我们比较通用的方法是包含头文件 windows.h，但包含后发现，lua库中的LoadString函数正好与windows  api LoadString同名。所以把lua库内部所使用的LoadString通通改为LUA_LoadString即可

修改完之后，在控制台写了四个线程一个一个主lua_state，四个线程使用lua_newthread得到的lua_state，没有再出现错误了。