java线程启动代码
????? 上次写了个《Thread的调用》过于简单，在这以javaThread的启动过程做一个详细分析。
????? 先从java/lang/Thread.java看起
?????? public synchronized void start() {
????????????? .....
????????????? start0(); //?? start0为本地方法 private native void start0();
??????????????.....
?????? }
??????
?????? 上面start0的具体实现是jvm.cpp中的JVM_StartThread。
?????? ......
?????? native_thread = new JavaThread(&thread_entry, sz);
?????? if (native_thread->osthread() != NULL) {
?????? ?????? native_thread->prepare(jthread);
?????? }
?????? .....
?????? Thread::start(native_thread);
???????
?????? 上面传入函数指针thread_entry，thread_entry就是调用Thread.java中的run方法，这就是java程序中只需要new Thread().start，虚拟机就调用run方法的原因。
?????? static void thread_entry(JavaThread* thread, TRAPS) {
??????????????????????? HandleMark hm(THREAD);
??????????????????????? Handle obj(THREAD, thread->threadObj());
????????????????????????JavaValue result(T_VOID);
??????????????????????? JavaCalls::call_virtual(&result,
????????????????????????????????????? obj,
????????????????????????????????????? KlassHandle(THREAD, SystemDictionary::thread_klass()),
????????????????????????????????????? vmSymbolHandles::run_method_name(),?//调用用户编写thread类run方法
????????????????????????????????????? vmSymbolHandles::void_method_signature(),
??????????????????????????????????????THREAD);
??????? }
??????? 再看new JavaThread(...)这步。
??????? JavaThread::JavaThread(ThreadFunction entry_point, size_t stack_sz) : Thread() {
???????????????? .........
???????????????? os::ThreadType thr_type = os::java_thread;
?????????????????thr_type = entry_point == &compiler_thread_entry ? os::compiler_thread :
???????????????????????????????????????????????????? os::java_thread;
?????????????????os::create_thread(this, thr_type, stack_sz);
??????? }
??????? 到了os::create_thread这步。
????????bool os::create_thread(Thread* thread, ThreadType thr_type, size_t stack_size) {
?????????????? OSThread* osthread = new OSThread(NULL, NULL);
?????????????? thread->set_osthread(osthread);
???????????????HANDLE thread_handle =
?????????????? (HANDLE)_beginthreadex(NULL,
?????????????????????????? (unsigned)stack_size,
?????????????????????????? (unsigned (__stdcall *)(void*)) java_start,
?????????????????????????? thread,
?????????????????????????? CREATE_SUSPENDED | STACK_SIZE_PARAM_IS_A_RESERVATION,
?????????????????????????? &thread_id);
?????????????? //上面创建线程的时候，线程不自动运行，而是堵塞，直到上面的Thread::start(native_thread)才开始运行
?????????????? .............
??????? }
??????? 再看启动函数java_start。
??????? static unsigned __stdcall java_start(Thread* thread) {
?????????????????? __try {
????????????????????????? thread->run();? //注意：传入的是javaThread，所以在这调用javaThread::run
?????????????????? } __except(topLevelExceptionFilter(
?????????????????????? (_EXCEPTION_POINTERS*)_exception_info())) {
???????????????????}
??????? }
??????? 查看
????????void JavaThread::run() {
????????????????? .......
????????????????? thread_main_inner();//在里面真正调用用户写的java类run方法
??????? }
??????? void JavaThread::thread_main_inner() {
???????????????? this->entry_point()(this, this); //调用传入thread_entry
???????????????? //退出
???????????????? this->exit(false);
???????????????? delete this;
??????? }
??????? 最后看一下
??????? void Thread::start(Thread* thread) {
??????????????? ........
??????????????? os::start_thread(thread); //运行创建时堵塞的线程
??????? }
?????? void os::start_thread(Thread* thread) {
????????????????.........
??????????????? OSThread* osthread = thread->osthread();
??????????????? osthread->set_state(RUNNABLE);
??????????????? pd_start_thread(thread);
?????? }
?????? void os::pd_start_thread(Thread* thread) {
???????????????//真正恢复操作系统线程运行的代码
?????????????? DWORD ret = ResumeThread(thread->osthread()->thread_handle());
?????? }
?????? 由上面可以看到每个继承java.lang.Thread的类，调用start之后，都和一个操作系统的线程进行绑定。
