windows lua 多線程 線程同步

今天在改一個程序，改成部分邏輯用lua寫，這個程序是多線程的。將程序中部分邏輯改成lua之后，各種非法訪問內存錯誤，各種奇奇怪怪的問題，不分時間，不分地點的出現崩潰。從調用堆棧來看，基本都是使用lua造成的。在多線程中使用lua_newthread得到的lus_State仍然有時候程序會崩潰。基本上可以確定為多線程中操作lua 的問題了。

前幾天我轉載的一篇文章，文章寫了關於lua多線程的作法。作法有二

1.每一個線程函數用lua_newthread產生一個新的lua_state 以后對lua操作都用這個lua_state

2.修改lua源碼使之成為支持多線程的（修改lua 源代碼中lua_lock lua_unlock宏）

對於第2條，那篇文中的例子是用 pthread_mutex_t 來進行線程同步的pthread_mutex_t，我對pthread_mutex_t 不熟，網上一查才知道一般是在linux下C語言進行線程同步用的，在windows下面一般多線程都用CRITICAL_SECTION，和內核對象來進行線程同步的。於是產生了這篇文章。

修改代碼如下：

1.global_State加一個成員變量  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的代碼 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 加入刪除CriticalSection的代碼 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.為了使用CRITICAL_SECTION我們比較通用的方法是包含頭文件 windows.h，但包含后發現，lua庫中的LoadString函數正好與windows  api LoadString同名。所以把lua庫內部所使用的LoadString通通改為LUA_LoadString即可

修改完之后，在控制台寫了四個線程一個一個主lua_state，四個線程使用lua_newthread得到的lua_state，沒有再出現錯誤了。