Lua中的线程和状态

local co = coroutine.create(function() print("hi") end)
print(co)  --output: thread: 0038BEE0

lua_State *lua_newstate (lua_Alloc f, void *ud);

lua_State *lua_newthread (lua_State *L);

    总之，一个Lua虚拟机只有一个全局的状态，但可以包含多个执行环境（或者说多个线程、交互栈，从脚本角度来说，也可以说是多个协程），也就是说多个执行环境共享一个全局状态。如下图所示：

下面将通过Lua 5.2.1的源码来看全局状态的数据结构global_State和脚本执行的相关的上下文环境结构lua_State，以及函数lua_newstate和lua_newthread的实现。

2、源码实现
    首先来分析全局状态的结构体global_State的代码（lstate.h）：

109 /*                                                                                                 
110 ** `global state', shared by all threads of this state                                             
111 */                                                                                                 
112 typedef struct global_State {                                                                      
113   lua_Alloc frealloc;  /* function to reallocate memory */                                         
114   void *ud;         /* auxiliary data to `frealloc' */                                             
115   lu_mem totalbytes;  /* number of bytes currently allocated - GCdebt */                           
116   l_mem GCdebt;  /* bytes allocated not yet compensated by the collector */                        
117   lu_mem GCmemtrav;  /* memory traversed by the GC */                                              
118   lu_mem GCestimate;  /* an estimate of the non-garbage memory in use */                           
119   stringtable strt;  /* hash table for strings */                                                  
120   TValue l_registry;                                                                               
121   unsigned int seed;  /* randomized seed for hashes */                                             
122   lu_byte currentwhite;                                                                            
123   lu_byte gcstate;  /* state of garbage collector */                                               
124   lu_byte gckind;  /* kind of GC running */                                                        
125   lu_byte gcrunning;  /* true if GC is running */                                                  
126   int sweepstrgc;  /* position of sweep in `strt' */                                               
127   GCObject *allgc;  /* list of all collectable objects */                                          
128   GCObject *finobj;  /* list of collectable objects with finalizers */                             
129   GCObject **sweepgc;  /* current position of sweep in list 'allgc' */                             
130   GCObject **sweepfin;  /* current position of sweep in list 'finobj' */                           
131   GCObject *gray;  /* list of gray objects */                                                      
132   GCObject *grayagain;  /* list of objects to be traversed atomically */                           
133   GCObject *weak;  /* list of tables with weak values */                                           
134   GCObject *ephemeron;  /* list of ephemeron tables (weak keys) */                                 
135   GCObject *allweak;  /* list of all-weak tables */                                                
136   GCObject *tobefnz;  /* list of userdata to be GC */                                              
137   UpVal uvhead;  /* head of double-linked list of all open upvalues */                             
138   Mbuffer buff;  /* temporary buffer for string concatenation */                                   
139   int gcpause;  /* size of pause between successive GCs */
140   int gcmajorinc;  /* how much to wait for a major GC (only in gen. mode) */
141   int gcstepmul;  /* GC `granularity' */
142   lua_CFunction panic;  /* to be called in unprotected errors */
143   struct lua_State *mainthread;
144   const lua_Number *version;  /* pointer to version number */
145   TString *memerrmsg;  /* memory-error message */
146   TString *tmname[TM_N];  /* array with tag-method names */
147   struct Table *mt[LUA_NUMTAGS];  /* metatables for basic types */
148 } global_State;

151 /*
152 ** `per thread' state
153 */
154 struct lua_State {
155   CommonHeader;
156   lu_byte status;
157   StkId top;  /* first free slot in the stack */
158   global_State *l_G;
159   CallInfo *ci;  /* call info for current function */
160   const Instruction *oldpc;  /* last pc traced */
161   StkId stack_last;  /* last free slot in the stack */
162   StkId stack;  /* stack base */ 
163   int stacksize;
164   unsigned short nny;  /* number of non-yieldable calls in stack */
165   unsigned short nCcalls;  /* number of nested C calls */
166   lu_byte hookmask;
167   lu_byte allowhook;
168   int basehookcount;
169   int hookcount;
170   lua_Hook hook;
171   GCObject *openupval;  /* list of open upvalues in this stack */
172   GCObject *gclist;
173   struct lua_longjmp *errorJmp;  /* current error recover point */
174   ptrdiff_t errfunc;  /* current error handling function (stack index) */
175   CallInfo base_ci;  /* CallInfo for first level (C calling Lua) */
176 };

    可以看到，lua_State结构跟其他可回收的数据类型类型，结构体带用CommonHeader的头，它也GC回收的对象之一。它主要包括以下成员信息：
lu_byte status：线程脚本的状态，线程可能状态如下（lua.h）：

 44 /* thread status */
 45 #define LUA_OK      0
 46 #define LUA_YIELD   1
 47 #define LUA_ERRRUN  2
 48 #define LUA_ERRSYNTAX   3
 49 #define LUA_ERRMEM  4
 50 #define LUA_ERRGCMM 5
 51 #define LUA_ERRERR  6

3、总结
    在调用lua_newstate 初始化Lua虚拟机时，会创建一个全局状态和一个线程（或称为调用栈），这个全局状态在整个虚拟机中是唯一的，供其他线程共享。一个Lua虚拟机中可以包括多个线程，这些线程共享一个全局状态，线程之间也可以调用lua_xmove函数来交换数据。

参考资料

http://www.cnblogs.com/ringofthec/archive/2010/11/09/lua_State.html lua API 小记3(lua虚拟机初始化)
http://blog.aliyun.com/795 Lua数据结构 — lua_State（六）
Lua 5.2.1源码

Lua中的线程和状态

原文：http://blog.csdn.net/maximuszhou/article/details/46277695