android开发分享Android开发App启动流程与消息机制详解

public static void main(string[] args) throws interruptedexception {          threadlocal<string> threadlocal = new threadlocal<string>(){              @override              protected string initialvalue() {                  return "data--1";              }          };          system.out.println("1主线程-->  "+threadlocal.get());          thread t1 = new thread(()->{          });          t1.start();          threadlocal.set("data--2");          system.out.println("2主线程-->  "+threadlocal.get());          thread t2 = new thread(()->{              system.out.println("线程2--->  "+threadlocal.get());          });          t2.start();          thread t3 = new thread(()->{              threadlocal.set("data-->3");              system.out.println("线程3--->  "+threadlocal.get());          });          t3.start();          system.out.println("3主线程-->  "+threadlocal.get());          thread.sleep(1000);      }  

//默认情况下initialvalue是返回为空的      protected t initialvalue() {          return null;      }  //在get的时候如果没有调用set方法  getmap(t);是返回为空的，所以，返回的是setinitialvalue(),这些方法请看后面的介绍，而setinitialvalue方法返回的其实就是初始值         public t get() {          thread t = thread.currentthread();          threadlocalmap map = getmap(t);          if (map != null) {              threadlocalmap.entry e = map.getentry(this);              if (e != null) {                  @suppresswarnings("unchecked")                  t result = (t)e.value;                  return result;              }          }          return setinitialvalue();      }      //这个方法在在调用的时候实际上getmap(t)是为空的，所以就会调用createmap，这个方法会把当前的线程作为值，保证getmap再调用就不会为空      public void set(t value) {          thread t = thread.currentthread();          threadlocalmap map = getmap(t);          if (map != null)              map.set(this, value);          else              createmap(t, value);      }

    private t setinitialvalue() {          t value = initialvalue();          thread t = thread.currentthread();          threadlocalmap map = getmap(t);          if (map != null)              map.set(this, value);          else              createmap(t, value);          return value;      }           public void remove() {           threadlocalmap m = getmap(thread.currentthread());           if (m != null)               m.remove(this);       }           threadlocalmap getmap(thread t) {          return t.threadlocals;      }          void createmap(thread t, t firstvalue) {          t.threadlocals = new threadlocalmap(this, firstvalue);      }  

//这是main函数的入口   public static void main(string[] args) {          trace.tracebegin(trace.trace_tag_activity_manager, "activitythreadmain");          samplingprofilerintegration.start();          // closeguard defaults to true and can be quite spammy.  we          // disable it here, but selectively enable it later (via          // strictmode) on debug builds, but using dropbox, not logs.          closeguard.setenabled(false);          environment.initforcurrentuser();          // set the reporter for event logging in libcore          eventlogger.setreporter(new eventloggingreporter());          // make sure trustedcertificatestore looks in the right place for ca certificates          final file configdir = environment.getuserconfigdirectory(userhandle.myuserid());          trustedcertificatestore.setdefaultuserdirectory(configdir);          process.setargv0("<pre-initialized>");          looper.preparemainlooper();          activitythread thread = new activitythread();          thread.attach(false);          if (smainthreadhandler == null) {              smainthreadhandler = thread.gethandler();          }          if (false) {              looper.mylooper().setmessagelogging(new                      logprinter(log.debug, "activitythread"));          }          // end of event activitythreadmain.          trace.traceend(trace.trace_tag_activity_manager);          looper.loop();          throw new runtimeexception("main thread loop unexpectedly exited");      }  

 /**       * initialize the current thread as a looper, marking it as an       * application's main looper. the main looper for your application       * is created by the android environment, so you should never need       * to call this function yourself.  see also: {@link #prepare()}       */      public static void preparemainlooper() {          prepare(false);          synchronized (looper.class) {              if (smainlooper != null) {                  throw new illegalstateexception("the main looper has already been prepared.");              }              smainlooper = mylooper();          }      }  

    /**       * return the looper object associated with the current thread.  returns       * null if the calling thread is not associated with a looper.       */      public static @nullable looper mylooper() {          return sthreadlocal.get();      }  

  // sthreadlocal.get() will return null unless you've called prepare().      static final threadlocal<looper> sthreadlocal = new threadlocal<looper>();  

    private static void prepare(boolean quitallowed) {          if (sthreadlocal.get() != null) {              throw new runtimeexception("only one looper may be created per thread");          }          sthreadlocal.set(new looper(quitallowed));      }  

    private looper(boolean quitallowed) {          mqueue = new messagequeue(quitallowed);          mthread = thread.currentthread();      }  

    private handler handler = new handler(){          @override          public void handlemessage(message msg) {              super.handlemessage(msg);          }      };  

        message message = new message();          handler.sendmessage(message);  	//点击去      public final boolean sendmessage(message msg)      {          return sendmessagedelayed(msg, 0);      }  	//点击去  	    public final boolean sendmessagedelayed(message msg, long delaymillis)      {          if (delaymillis < 0) {              delaymillis = 0;          }          return sendmessageattime(msg, systemclock.uptimemillis() + delaymillis);      }  

//继续看sendmessageattime      public boolean sendmessageattime(message msg, long uptimemillis) {          messagequeue queue = mqueue;          if (queue == null) {              runtimeexception e = new runtimeexception(                      this + " sendmessageattime() called with no mqueue");              log.w("looper", e.getmessage(), e);              return false;          }          return enqueuemessage(queue, msg, uptimemillis);      }          private boolean enqueuemessage(messagequeue queue, message msg, long uptimemillis) {          msg.target = this;          if (masynchronous) {              msg.setasynchronous(true);          }          return queue.enqueuemessage(msg, uptimemillis);      }  

    //我们看到了enqueuemessage，我们看这个queue在哪里获取的          public handler(callback callback, boolean async) {          if (find_potential_leaks) {              final class<? extends handler> klass = getclass();              if ((klass.isanonymousclass() || klass.ismemberclass() || klass.islocalclass()) &&                      (klass.getmodifiers() & modifier.static) == 0) {                  log.w(tag, "the following handler class should be static or leaks might occur: " +                      klass.getcanonicalname());              }          }          mlooper = looper.mylooper();          if (mlooper == null) {              throw new runtimeexception(                  "can't create handler inside thread that has not called looper.prepare()");          }          mqueue = mlooper.mqueue;          mcallback = callback;          masynchronous = async;      }