线程初始化

淩亂°似流年 2022-01-06 04:33 164阅读 0赞

### 目录 ###

private void init(ThreadGroup g, Runnable target, String name,
                          long stackSize, AccessControlContext acc,
                          boolean inheritThreadLocals) { 
            if (name == null) { 
                throw new NullPointerException("name cannot be null");
            }
    
            this.name = name;
    		//当前线程就是该线程的父线程
            Thread parent = currentThread();
            SecurityManager security = System.getSecurityManager();
            if (g == null) { 
                /* Determine if it's an applet or not */
    
                /* If there is a security manager, ask the security manager what to do. */
                if (security != null) { 
                    g = security.getThreadGroup();
                }
    
                /* If the security doesn't have a strong opinion of the matter use the parent thread group. */
                if (g == null) { 
                    g = parent.getThreadGroup();
                }
            }
    
            /* checkAccess regardless of whether or not threadgroup is explicitly passed in. */
            g.checkAccess();
    
            /* * Do we have the required permissions? */
            if (security != null) { 
                if (isCCLOverridden(getClass())) { 
                    security.checkPermission(SUBCLASS_IMPLEMENTATION_PERMISSION);
                }
            }
    
            g.addUnstarted();
    
            this.group = g;
            // 将daemon、priority属性设置为父线程的对应属性
            this.daemon = parent.isDaemon();
            this.priority = parent.getPriority();
            if (security == null || isCCLOverridden(parent.getClass()))
                this.contextClassLoader = parent.getContextClassLoader();
            else
                this.contextClassLoader = parent.contextClassLoader;
            this.inheritedAccessControlContext =
                    acc != null ? acc : AccessController.getContext();
            this.target = target;
            setPriority(priority);
            // 将父线程的InheritableThreadLocal复制过来
            if (inheritThreadLocals && parent.inheritableThreadLocals != null)
                this.inheritableThreadLocals =
                    ThreadLocal.createInheritedMap(parent.inheritableThreadLocals);
            /* Stash the specified stack size in case the VM cares */
            this.stackSize = stackSize;
    
            /* 分配一个线程id */
            tid = nextThreadID();
        }

> 在上述过程中，一个新构造的线程对象是由其parent线程来进行空间分配的，而  
> child线程继承了parent是否为Daemon、优先级和加载资源的contextClassLoader  
> 以及可继承的ThreadLoacl,同时还会分配一个唯一的ID来标识这个child线程。  
> 至此，一个能够运行的 线程对象就初始化好了，在堆内存中等待这运行。

> 线程对象在初始化完成之后，调用start(）方法就可以启动这个线程。  
> 线程start(）方法的含义是：当前线程（即parent线程）同步告知Java虚拟机，只要线程规划空闲，应立即启动调用start(）方法的线程