IPC thread写法太晦涩

主要用到TLS，首次进入gHaveTLS为false，锁保护说明此函数很多其他函数在调用。
通过if (pthread_key_create(&gTLS, threadDestructor) != 0)，中threadDestructor(void *st)
调用IPCThreadState::IPCThreadState()创建IPCThreadState对象，并将对象的索引设置为gTLS。再次进入后通过gTLS获取到IPCThreadState对象。

 1 IPCThreadState* IPCThreadState::self()
 2 {
 3     if (gHaveTLS) {
 4 restart:
 5         const pthread_key_t k = gTLS;
 6         IPCThreadState* st = (IPCThreadState*)pthread_getspecific(k);
 7         if (st) return st;
 8         return new IPCThreadState;
 9     }
10     
11     if (gShutdown) return NULL;
12     
13     pthread_mutex_lock(&gTLSMutex);
14     if (!gHaveTLS) {
15         if (pthread_key_create(&gTLS, threadDestructor) != 0) {
16             pthread_mutex_unlock(&gTLSMutex);
17             return NULL;
18         }
19         gHaveTLS = true;
20     }
21     pthread_mutex_unlock(&gTLSMutex);
22     goto restart;
23 }

 1 IPCThreadState::IPCThreadState()
 2     : mProcess(ProcessState::self()),
 3       mMyThreadId(androidGetTid()),
 4       mStrictModePolicy(0),
 5       mLastTransactionBinderFlags(0)
 6 {
 7     pthread_setspecific(gTLS, this);
 8     clearCaller();
 9     mIn.setDataCapacity(256);
10     mOut.setDataCapacity(256);
11 }