Java高并发编程基础之Thread构造函数大有内涵

    public Thread() {
        this(null, null, "Thread-" + nextThreadNum(), 0);
    }

    public Thread(Runnable target) {
        this(null, target, "Thread-" + nextThreadNum(), 0);
    }

    Thread(Runnable target, @SuppressWarnings("removal") AccessControlContext acc) {
        this(null, target, "Thread-" + nextThreadNum(), 0, acc, false);
    }

    public Thread(ThreadGroup group, Runnable target) {
        this(group, target, "Thread-" + nextThreadNum(), 0);
    }

    public Thread(String name) {
        this(null, null, name, 0);
    }

    public Thread(ThreadGroup group, String name) {
        this(group, null, name, 0);
    }

    public Thread(Runnable target, String name) {
        this(null, target, name, 0);
    }

    public Thread(ThreadGroup group, Runnable target, String name) {
        this(group, target, name, 0);
    }

    public Thread(ThreadGroup group, Runnable target, String name,
                  long stackSize) {
        this(group, target, name, stackSize, null, true);
    }

    public Thread(ThreadGroup group, Runnable target, String name,
                  long stackSize, boolean inheritThreadLocals) {
        this(group, target, name, stackSize, null, inheritThreadLocals);
    }

    /**
     * Allocates a new {@code Thread} object. This constructor has the same
     * effect as {@linkplain #Thread(ThreadGroup,Runnable,String) Thread}
     * {@code (null, null, gname)}, where {@code gname} is a newly generated
     * name. Automatically generated names are of the form
     * {@code "Thread-"+}<i>n</i>, where <i>n</i> is an integer.
     */
    public Thread() {
        this(null, null, "Thread-" + nextThreadNum(), 0);
    }

    /**
     * Allocates a new {@code Thread} object. This constructor has the same
     * effect as {@linkplain #Thread(ThreadGroup,Runnable,String) Thread}
     * {@code (null, target, gname)}, where {@code gname} is a newly generated
     * name. Automatically generated names are of the form
     * {@code "Thread-"+}<i>n</i>, where <i>n</i> is an integer.
     *
     * @param  target
     *         the object whose {@code run} method is invoked when this thread
     *         is started. If {@code null}, this classes {@code run} method does
     *         nothing.
     */
    public Thread(Runnable target) {
        this(null, target, "Thread-" + nextThreadNum(), 0);
    }

    /**
     * Allocates a new {@code Thread} object. This constructor has the same
     * effect as {@linkplain #Thread(ThreadGroup,Runnable,String) Thread}
     * {@code (group, target, gname)} ,where {@code gname} is a newly generated
     * name. Automatically generated names are of the form
     * {@code "Thread-"+}<i>n</i>, where <i>n</i> is an integer.
     *
     * @param  group
     *         the thread group. If {@code null} and there is a security
     *         manager, the group is determined by {@linkplain
     *         SecurityManager#getThreadGroup SecurityManager.getThreadGroup()}.
     *         If there is not a security manager or {@code
     *         SecurityManager.getThreadGroup()} returns {@code null}, the group
     *         is set to the current thread's thread group.
     *
     * @param  target
     *         the object whose {@code run} method is invoked when this thread
     *         is started. If {@code null}, this thread's run method is invoked.
     *
     * @throws  SecurityException
     *          if the current thread cannot create a thread in the specified
     *          thread group
     */
    public Thread(ThreadGroup group, Runnable target) {
        this(group, target, "Thread-" + nextThreadNum(), 0);
    }

    /**
     * Allocates a new {@code Thread} object. This constructor has the same
     * effect as {@linkplain #Thread(ThreadGroup,Runnable,String) Thread}
     * {@code (null, null, name)}.
     *
     * @param   name
     *          the name of the new thread
     */
    public Thread(String name) {
        this(null, null, name, 0);
    }
/**
     * Allocates a new {@code Thread} object. This constructor has the same
     * effect as {@linkplain #Thread(ThreadGroup,Runnable,String) Thread}
     * {@code (group, null, name)}.
     *
     * @param  group
     *         the thread group. If {@code null} and there is a security
     *         manager, the group is determined by {@linkplain
     *         SecurityManager#getThreadGroup SecurityManager.getThreadGroup()}.
     *         If there is not a security manager or {@code
     *         SecurityManager.getThreadGroup()} returns {@code null}, the group
     *         is set to the current thread's thread group.
     *
     * @param  name
     *         the name of the new thread
     *
     * @throws  SecurityException
     *          if the current thread cannot create a thread in the specified
     *          thread group
     */
    public Thread(ThreadGroup group, String name) {
        this(group, null, name, 0);
    }

    /**
     * Allocates a new {@code Thread} object. This constructor has the same
     * effect as {@linkplain #Thread(ThreadGroup,Runnable,String) Thread}
     * {@code (null, target, name)}.
     *
     * @param  target
     *         the object whose {@code run} method is invoked when this thread
     *         is started. If {@code null}, this thread's run method is invoked.
     *
     * @param  name
     *         the name of the new thread
     */
    public Thread(Runnable target, String name) {
        this(null, target, name, 0);
    }

    /**
     *
     * @param  group
     *         the thread group. If {@code null} and there is a security
     *         manager, the group is determined by {@linkplain
     *         SecurityManager#getThreadGroup SecurityManager.getThreadGroup()}.
     *         If there is not a security manager or {@code
     *         SecurityManager.getThreadGroup()} returns {@code null}, the group
     *         is set to the current thread's thread group.
     *
     * @param  target
     *         the object whose {@code run} method is invoked when this thread
     *         is started. If {@code null}, this thread's run method is invoked.
     *
     * @param  name
     *         the name of the new thread
     *
     * @throws  SecurityException
     *          if the current thread cannot create a thread in the specified
     *          thread group or cannot override the context class loader methods.
     */
    public Thread(ThreadGroup group, Runnable target, String name) {
        this(group, target, name, 0);
    }

    /**
     * Changes the name of this thread to be equal to the argument {@code name}.
     * <p>
     * First the {@code checkAccess} method of this thread is called
     * with no arguments. This may result in throwing a
     * {@code SecurityException}.
     *
     * @param      name   the new name for this thread.
     * @throws     SecurityException  if the current thread cannot modify this
     *             thread.
     * @see        #getName
     * @see        #checkAccess()
     */
    public final synchronized void setName(String name) {
        checkAccess();
        if (name == null) {
            throw new NullPointerException("name cannot be null");
        }

        this.name = name;
        if (threadStatus != 0) {
            setNativeName(name);
        }
    }

/**
     * Initializes a Thread.
     *
     * @param g the Thread group
     * @param target the object whose run() method gets called
     * @param name the name of the new Thread
     * @param stackSize the desired stack size for the new thread, or
     *        zero to indicate that this parameter is to be ignored.
     * @param acc the AccessControlContext to inherit, or
     *            AccessController.getContext() if null
     * @param inheritThreadLocals if {@code true}, inherit initial values for
     *            inheritable thread-locals from the constructing thread
     */
    @SuppressWarnings("removal")
    private Thread(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;

        Thread parent = currentThread(); // 调用获取当前线程函数
        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 manager doesn't have a strong opinion
               on 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(
                        SecurityConstants.SUBCLASS_IMPLEMENTATION_PERMISSION);
            }
        }

        g.addUnstarted();

        this.group = g;
        this.daemon = parent.isDaemon();// 通过父线程守护参数设置当前线程守护线程参数
        this.priority = parent.getPriority();// 通过父线程参数设置当前线程优先级参数
        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);
        if (inheritThreadLocals && parent.inheritableThreadLocals != null)
            this.inheritableThreadLocals =
                ThreadLocal.createInheritedMap(parent.inheritableThreadLocals);
        /* Stash the specified stack size in case the VM cares */
        this.stackSize = stackSize;

        /* Set thread ID */
        this.tid = nextThreadID();
    }

Thread parent = currentThread(); // 调用获取当前线程函数
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 manager doesn't have a strong opinion
        on 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(
                SecurityConstants.SUBCLASS_IMPLEMENTATION_PERMISSION);
    }
}

g.addUnstarted();

this.group = g;

package engineer.concurrent.battle.onebasic;

/**
 * 测试 Thread 与 ThreadGroup
 */
public class ThreadGroupTest {
    public static void main(String[] args) {
        Thread t1 = new Thread("t1");
        ThreadGroup group = new ThreadGroup("group1");
        Thread t2 = new Thread(group,"t2");
        ThreadGroup mainThreadGroup = Thread.currentThread().getThreadGroup();
        System.out.println("Main thread belong group:"+ mainThreadGroup.getName());
        System.out.println("tl and main belong the same group:" + (mainThreadGroup== t1.getThreadGroup()));
        System.out.println("t2 thread group not belong main group:" + (mainThreadGroup== t2.getThreadGroup()));
        System.out.println("t2 thread group belong main TestGroup:" + (group == t2.getThreadGroup()));
    }
}

Main thread belong group:main
tl and main belong the same group:true
t2 thread group not belong main group:false
t2 thread group belong main TestGroup:true

The stack size is the approximate number of bytes of address space that the virtual machine is to allocate for this thread's stack. The effect of the stackSize parameter, if any, is highly platform dependent.

On some platforms, specifying a higher value for the stackSize parameter may allow a thread to achieve greater recursion depth before throwing a StackOverflowError. Similarly, specifying a lower value may allow a greater number of threads to exist concurrently without throwing an OutOfMemoryError (or other internal error). The details of the relationship between the value of the stackSize parameter and the maximum recursion depth and concurrency level are platform-dependent. On some platforms, the value of the stackSize parameter may have no effect whatsoever.

The virtual machine is free to treat the stackSize parameter as a suggestion. If the specified value is unreasonably low for the platform, the virtual machine may instead use some platform-specific minimum value; if the specified value is unreasonably high, the virtual machine may instead use some platform-specific maximum. Likewise, the virtual machine is free to round the specified value up or down as it sees fit (or to ignore it completely).

Specifying a value of zero for the stackSize parameter will cause this constructor to behave exactly like the Thread(ThreadGroup, Runnable, String) constructor.

Due to the platform-dependent nature of the behavior of this constructor, extreme care should be exercised in its use. The thread stack size necessary to perform a given computation will likely vary from one JRE implementation to another. In light of this variation, careful tuning of the stack size parameter may be required, and the tuning may need to be repeated for each JRE implementation on which an application is to run.

Implementation note: Java platform implementers are encouraged to document their implementation's behavior with respect to the stackSize parameter.

堆栈大小是虚拟机为该线程的堆栈分配的大致字节数。stackSize参数的效果在很大程度上取决于平台。

在某些平台上，为stackSize参数指定较高的值可能允许线程在引发StackOverflowError之前实现更大的递归深度。同样，指定较低的值可能允许更多的线程并发存在，而不会引发OutOfMemoryError（或其他内部错误）。stackSize参数的值与最大递归深度和并发级别之间的关系细节因平台而异。在某些平台上，stackSize参数的值可能根本不起作用。

虚拟机可以将stackSize参数视为建议。如果指定的值对于平台来说过低，虚拟机可能会使用一些特定于平台的最小值；如果指定的值过高，虚拟机可能会使用一些特定于平台的最大值。同样地，虚拟机可以自行决定是否将指定的值向上舍入或向下舍入（或完全忽略它）。

对于stackSize参数设置为0，该构造函数的行为将与Thread(ThreadGroup, Runnable, String)构造函数完全相同。

由于此构造函数的行为依赖于平台，使用时应极度谨慎。执行给定计算所需的线程堆栈大小可能因JRE实现而异。鉴于这种差异，可能需要对stackSize参数进行仔细调整，并且在应用程序要运行的每个JRE实现上可能需要重复调整。

实施注意事项：鼓励Java平台实现者记录其实现与stackSize参数相关的行为。

package engineer.concurrent.battle.onebasic;
import org.junit.jupiter.api.Test;

public class ThreadStackSizeTest {
    private final static int THREAD_COUNT = Integer.MAX_VALUE;
    @Test
    public void testStackSize1() {
        // 6914
        stackSizeRunMethod(10);
    }

    @Test
    public void testStackSize2() {
        // 4009
        stackSizeRunMethod(100);
    }

    @Test
    public void testStackSize3() {
        //6461
        stackSizeRunMethod(1000);
    }

    @Test
    public void testStackSize4() {
        //153
        stackSizeRunMethod(10000);
    }

    public static void stackSizeRunMethod(int stackSize) {
        ThreadGroup group = new ThreadGroup("stackSizeRunMethod");
        Runnable runnable = new Runnable() {
            public void run() {
                int i = 1;
                try {
                    recurse(i);
                } catch (Exception e) {
                    System.out.println(e.getMessage());
                } catch (Error e) {
                    System.out.println(e.getMessage());
                }
            }
            private void recurse(int i) {
                System.out.println(i);
                if (i < THREAD_COUNT) {
                    recurse(i + 1);
                }
            }
        };
        Thread thread = new Thread(group, runnable, "ThreadStackSizeTest", stackSize);
        thread.start();
    }
}

package engineer.concurrent.battle.onebasic;

public class DaemonThread {

    public static void main(String[] args) throws InterruptedException {
        Thread thread = new Thread(() -> {
            while (true) {
                System.out.println("I am a daemon thread");
                try {
                    Thread.sleep(1000);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        });
        // 将线程设置为守护线程
        thread.setDaemon(true);
        thread.start();
        Thread.sleep(2000);
        System.out.println("I am main thread and end");
    }
}