Threads have names to identify them. These names are not necessarily * unique. Every Thread has a priority, as well, which tells the VM which * Threads should get more running time. New threads inherit the priority * and daemon status of the parent thread, by default. * *
There are two methods of creating a Thread: you may subclass Thread and
* implement the run() method, at which point you may start the
* Thread by calling its start() method, or you may implement
* Runnable in the class you want to use and then call new
* Thread(your_obj).start().
*
*
The virtual machine runs until all non-daemon threads have died (either
* by returning from the run() method as invoked by start(), or by throwing
* an uncaught exception); or until System.exit is called with
* adequate permissions.
*
*
It is unclear at what point a Thread should be added to a ThreadGroup,
* and at what point it should be removed. Should it be inserted when it
* starts, or when it is created? Should it be removed when it is suspended
* or interrupted? The only thing that is clear is that the Thread should be
* removed when it is stopped.
*
* @author Tom Tromey
* @author John Keiser
* @author Eric Blake If the thread is waiting because of {@link #wait()},
* {@link #sleep(long)}, or {@link #join()}, its interrupt status
* will be cleared, and an InterruptedException will be thrown. Notice that
* this case is only possible if an external thread called interrupt().
*
* If the thread is blocked in an interruptible I/O operation, in
* {@link java.nio.channels.InterruptibleChannel}, the interrupt
* status will be set, and ClosedByInterruptException will be thrown.
*
* If the thread is blocked on a {@link java.nio.channels.Selector}, the
* interrupt status will be set, and the selection will return, with
* a possible non-zero value, as though by the wakeup() method.
*
* Otherwise, the interrupt status will be set.
*
* @throws SecurityException if you cannot modify this Thread
*/
public native void interrupt ();
/**
* Determine whether the current Thread has been interrupted, and clear
* the interrupted status in the process.
*
* @return whether the current Thread has been interrupted
* @see #isInterrupted()
*/
public static boolean interrupted ()
{
return currentThread().isInterrupted (true);
}
/**
* Determine whether the given Thread has been interrupted, but leave
* the interrupted status alone in the process.
*
* @return whether the current Thread has been interrupted
* @see #interrupted()
*/
public boolean isInterrupted ()
{
return interrupt_flag;
}
/**
* Determine whether this Thread is alive. A thread which is alive has
* started and not yet died.
*
* @return whether this Thread is alive
*/
public final boolean isAlive ()
{
return alive_flag;
}
/**
* Tell whether this is a daemon Thread or not.
*
* @return whether this is a daemon Thread or not
* @see #setDaemon(boolean)
*/
public final boolean isDaemon ()
{
return daemon_flag;
}
/**
* Wait forever for the Thread in question to die.
*
* @throws InterruptedException if the Thread is interrupted; it's
* interrupted status will be cleared
*/
public final void join () throws InterruptedException
{
join (0, 0);
}
/**
* Wait the specified amount of time for the Thread in question to die.
*
* @param ms the number of milliseconds to wait, or 0 for forever
* @throws InterruptedException if the Thread is interrupted; it's
* interrupted status will be cleared
*/
public final void join (long timeout) throws InterruptedException
{
join (timeout, 0);
}
/**
* Wait the specified amount of time for the Thread in question to die.
*
* Note that 1,000,000 nanoseconds == 1 millisecond, but most VMs do
* not offer that fine a grain of timing resolution. Besides, there is
* no guarantee that this thread can start up immediately when time expires,
* because some other thread may be active. So don't expect real-time
* performance.
*
* @param ms the number of milliseconds to wait, or 0 for forever
* @param ns the number of extra nanoseconds to sleep (0-999999)
* @throws InterruptedException if the Thread is interrupted; it's
* interrupted status will be cleared
* @throws IllegalArgumentException if ns is invalid
* @XXX A ThreadListener would be nice, to make this efficient.
*/
public final native void join (long timeout, int nanos)
throws InterruptedException;
/**
* Resume a suspended thread.
*
* @see #resume()
* @deprecated pointless, since suspend is deprecated
*/
public final native void resume ();
private final native void finish_ ();
/**
* Determine whether the given Thread has been interrupted, but leave
* the interrupted status alone in the process.
*
* @return whether the current Thread has been interrupted
* @see #interrupted()
*/
private boolean isInterrupted (boolean clear_flag)
{
boolean r = interrupt_flag;
if (clear_flag && r)
{
// Only clear the flag if we saw it as set. Otherwise this could
// potentially cause us to miss an interrupt in a race condition,
// because this method is not synchronized.
interrupt_flag = false;
}
return r;
}
/**
* The method of Thread that will be run if there is no Runnable object
* associated with the Thread. Thread's implementation does nothing at all.
*
* @see #start()
* @see #Thread(ThreadGroup, Runnable, String)
*/
public void run ()
{
if (runnable != null)
runnable.run();
}
/**
* Set the daemon status of this Thread. If this is a daemon Thread, then
* the VM may exit even if it is still running. This may only be called
* before the Thread starts running. There may be a security check,
* Note that 1,000,000 nanoseconds == 1 millisecond, but most VMs do
* not offer that fine a grain of timing resolution. Besides, there is
* no guarantee that this thread can start up immediately when time expires,
* because some other thread may be active. So don't expect real-time
* performance.
*
* @param ms the number of milliseconds to sleep, or 0 for forever
* @param ns the number of extra nanoseconds to sleep (0-999999)
* @throws InterruptedException if the Thread is interrupted; it's
* interrupted status will be cleared
* @throws IllegalArgumentException if ns is invalid
* @see #notify()
* @see #wait(long, int)
*/
public static native void sleep (long timeout, int nanos)
throws InterruptedException;
/**
* Start this Thread, calling the run() method of the Runnable this Thread
* was created with, or else the run() method of the Thread itself. This
* is the only way to start a new thread; calling run by yourself will just
* stay in the same thread. The virtual machine will remove the thread from
* its thread group when the run() method completes.
*
* @throws IllegalThreadStateException if the thread has already started
* @see #run()
*/
public native void start ();
/**
* Cause this Thread to stop abnormally because of the throw of a ThreadDeath
* error. If you stop a Thread that has not yet started, it will stop
* immediately when it is actually started.
*
* This is inherently unsafe, as it can interrupt synchronized blocks and
* leave data in bad states. Hence, there is a security check:
* This is inherently unsafe, as it can interrupt synchronized blocks and
* leave data in bad states. Hence, there is a security check:
* This is inherently unsafe, as the suspended thread still holds locks,
* and can potentially deadlock your program. Hence, there is a security
* check: If the ThreadGroup is null, the security manager is checked. If a
* manager exists and returns a non-null object for
* The new Thread will inherit its creator's priority and daemon status.
* These can be changed with
* Threads created this way must have overridden their
* currentThread().getThreadGroup().activeCount().
*
* @return the number of active threads in the current ThreadGroup
* @see ThreadGroup#activeCount()
*/
public static int activeCount ()
{
return currentThread().getThreadGroup().activeCount();
}
/**
* Check whether the current Thread is allowed to modify this Thread. This
* passes the check on to SecurityManager.checkAccess(this).
*
* @throws SecurityException if the current Thread cannot modify this Thread
* @see SecurityManager#checkAccess(Thread)
*/
public final void checkAccess ()
{
SecurityManager s = System.getSecurityManager();
if (s != null)
s.checkAccess(this);
}
/**
* Count the number of stack frames in this Thread. The Thread in question
* must be suspended when this occurs.
*
* @return the number of stack frames in this Thread
* @throws IllegalThreadStateException if this Thread is not suspended
* @deprecated pointless, since suspend is deprecated
*/
public native int countStackFrames ();
/**
* Get the currently executing Thread.
*
* @return the currently executing Thread
*/
public static native Thread currentThread ();
/**
* Originally intended to destroy this thread, this method was never
* implemented by Sun, and is hence a no-op.
*/
public native void destroy ();
/**
* Print a stack trace of the current thread to stderr using the same
* format as Throwable's printStackTrace() method.
*
* @see Throwable#printStackTrace()
*/
public static void dumpStack ()
{
(new Exception ("Stack trace")).printStackTrace ();
}
/**
* Copy every active thread in the current Thread's ThreadGroup into the
* array. Extra threads are silently ignored. This implementation calls
* getThreadGroup().enumerate(array), which may have a
* security check, checkAccess(group).
*
* @param array the array to place the Threads into
* @return the number of Threads placed into the array
* @throws NullPointerException if array is null
* @throws SecurityException if you cannot access the ThreadGroup
* @see ThreadGroup#enumerate(Thread[])
* @see #activeCount()
* @see SecurityManager#checkAccess(ThreadGroup)
*/
public static int enumerate (Thread[] threads)
{
return currentThread().group.enumerate(threads);
}
/**
* Get this Thread's name.
*
* @return this Thread's name
*/
public final String getName ()
{
return name;
}
/**
* Get this Thread's priority.
*
* @return the Thread's priority
*/
public final int getPriority ()
{
return priority;
}
/**
* Get the ThreadGroup this Thread belongs to. If the thread has died, this
* returns null.
*
* @return this Thread's ThreadGroup
*/
public final ThreadGroup getThreadGroup ()
{
return group;
}
/**
* Interrupt this Thread. First, there is a security check,
* checkAccess. Then, depending on the current state of the
* thread, various actions take place:
*
* checkAccess.
*
* @param daemon whether this should be a daemon thread or not
* @throws SecurityException if you cannot modify this Thread
* @throws IllegalThreadStateException if the Thread is active
* @see #isDaemon()
* @see #checkAccess()
*/
public final void setDaemon (boolean status)
{
checkAccess ();
if (!startable_flag)
throw new IllegalThreadStateException ();
daemon_flag = status;
}
/**
* Returns the context classloader of this Thread. The context
* classloader can be used by code that want to load classes depending
* on the current thread. Normally classes are loaded depending on
* the classloader of the current class. There may be a security check
* for RuntimePermission("getClassLoader") if the caller's
* class loader is not null or an ancestor of this thread's context class
* loader.
*
* @return the context class loader
* @throws SecurityException when permission is denied
* @see setContextClassLoader(ClassLoader)
* @since 1.2
*/
public synchronized ClassLoader getContextClassLoader()
{
if (context_class_loader == null)
context_class_loader = ClassLoader.getSystemClassLoader ();
SecurityManager s = System.getSecurityManager();
// FIXME: we can't currently find the caller's class loader.
ClassLoader callers = null;
if (s != null && callers != null)
{
// See if the caller's class loader is the same as or an
// ancestor of this thread's class loader.
while (callers != null && callers != context_class_loader)
{
// FIXME: should use some internal version of getParent
// that avoids security checks.
callers = callers.getParent ();
}
if (callers != context_class_loader)
s.checkPermission (new RuntimePermission ("getClassLoader"));
}
return context_class_loader;
}
/**
* Returns the context classloader of this Thread. The context
* classloader can be used by code that want to load classes depending
* on the current thread. Normally classes are loaded depending on
* the classloader of the current class. There may be a security check
* for RuntimePermission("getClassLoader") if the caller's
* class loader is not null or an ancestor of this thread's context class
* loader.
*
* @return the context class loader
* @throws SecurityException when permission is denied
* @see setContextClassLoader(ClassLoader)
* @since 1.2
*/
public synchronized void setContextClassLoader(ClassLoader cl)
{
SecurityManager s = System.getSecurityManager ();
if (s != null)
s.checkPermission (new RuntimePermission ("setContextClassLoader"));
context_class_loader = cl;
}
/**
* Set this Thread's name. There may be a security check,
* checkAccess.
*
* @param name the new name for this Thread
* @throws NullPointerException if name is null
* @throws SecurityException if you cannot modify this Thread
*/
public final void setName (String n)
{
checkAccess ();
// The Class Libraries book says ``threadName cannot be null''. I
// take this to mean NullPointerException.
if (n == null)
throw new NullPointerException ();
name = n;
}
/**
* Set this Thread's priority. There may be a security check,
* checkAccess, then the priority is set to the smaller of
* priority and the ThreadGroup maximum priority.
*
* @param priority the new priority for this Thread
* @throws IllegalArgumentException if priority exceeds MIN_PRIORITY or
* MAX_PRIORITY
* @throws SecurityException if you cannot modify this Thread
* @see #getPriority()
* @see #checkAccess()
* @see ThreadGroup#getMaxPriority()
* @see #MIN_PRIORITY
* @see #MAX_PRIORITY
*/
public final native void setPriority (int newPriority);
/**
* Suspend the current Thread's execution for the specified amount of
* time. The Thread will not lose any locks it has during this time. There
* are no guarantees which thread will be next to run, but most VMs will
* choose the highest priority thread that has been waiting longest.
*
* @param ms the number of milliseconds to sleep, or 0 for forever
* @throws InterruptedException if the Thread is interrupted; it's
* interrupted status will be cleared
* @see #notify()
* @see #wait(long)
*/
public static void sleep (long timeout) throws InterruptedException
{
sleep (timeout, 0);
}
/**
* Suspend the current Thread's execution for the specified amount of
* time. The Thread will not lose any locks it has during this time. There
* are no guarantees which thread will be next to run, but most VMs will
* choose the highest priority thread that has been waiting longest.
*
* checkAccess(this), plus another one if the current thread
* is not this: RuntimePermission("stopThread"). If you must
* catch a ThreadDeath, be sure to rethrow it after you have cleaned up.
* ThreadDeath is the only exception which does not print a stack trace when
* the thread dies.
*
* @throws SecurityException if you cannot stop the Thread
* @see #interrupt()
* @see #checkAccess()
* @see #start()
* @see ThreadDeath
* @see ThreadGroup#uncaughtException(Thread, Throwable)
* @see SecurityManager#checkAccess(Thread)
* @see SecurityManager#checkPermission(Permission)
* @deprecated unsafe operation, try not to use
*/
public final void stop ()
{
// Argument doesn't matter, because this is no longer
// supported.
stop (null);
}
/**
* Cause this Thread to stop abnormally and throw the specified exception.
* If you stop a Thread that has not yet started, it will stop immediately
* when it is actually started. WARNINGThis bypasses Java security,
* and can throw a checked exception which the call stack is unprepared to
* handle. Do not abuse this power.
*
* checkAccess(this), plus another one if the current thread
* is not this: RuntimePermission("stopThread"). If you must
* catch a ThreadDeath, be sure to rethrow it after you have cleaned up.
* ThreadDeath is the only exception which does not print a stack trace when
* the thread dies.
*
* @param t the Throwable to throw when the Thread dies
* @throws SecurityException if you cannot stop the Thread
* @throws NullPointerException in the calling thread, if t is null
* @see #interrupt()
* @see #checkAccess()
* @see #start()
* @see ThreadDeath
* @see ThreadGroup#uncaughtException(Thread, Throwable)
* @see SecurityManager#checkAccess(Thread)
* @see SecurityManager#checkPermission(Permission)
* @deprecated unsafe operation, try not to use
*/
public final native void stop (Throwable e);
/**
* Suspend this Thread. It will not come back, ever, unless it is resumed.
*
* checkAccess.
*
* @throws SecurityException if you cannot suspend the Thread
* @see #checkAccess()
* @see #resume()
* @deprecated unsafe operation, try not to use
*/
public final native void suspend ();
private final native void initialize_native ();
private final native static String gen_name ();
/**
* Allocate a new Thread object, with the specified ThreadGroup and name, and
* using the specified Runnable object's run() method to
* execute. If the Runnable object is null, this (which is
* a Runnable) is used instead.
*
* getThreadGroup, that group is used; otherwise the group
* of the creating thread is used. Note that the security manager calls
* checkAccess if the ThreadGroup is not null.
*
* setPriority and
* setDaemon.
*
* @param group the group to put the Thread into
* @param target the Runnable object to execute
* @param name the name for the Thread
* @throws NullPointerException if name is null
* @throws SecurityException if this thread cannot access group
* @throws IllegalThreadStateException if group is destroyed
* @see Runnable#run()
* @see #run()
* @see #setDaemon(boolean)
* @see #setPriority(int)
* @see SecurityManager#checkAccess(ThreadGroup)
* @see ThreadGroup#checkAccess()
*/
public Thread (ThreadGroup g, Runnable r, String n)
{
this (currentThread (), g, r, n);
}
/**
* Allocate a new Thread object, as if by
* Thread(group, null, name), and give it the specified stack
* size, in bytes. The stack size is highly platform independent,
* and the virtual machine is free to round up or down, or ignore it
* completely. A higher value might let you go longer before a
* StackOverflowError, while a lower value might let you go
* longer before an OutOfMemoryError. Or, it may do absolutely
* nothing! So be careful, and expect to need to tune this value if your
* virtual machine even supports it.
*
* @param group the group to put the Thread into
* @param target the Runnable object to execute
* @param name the name for the Thread
* @param size the stack size, in bytes; 0 to be ignored
* @throws NullPointerException if name is null
* @throws SecurityException if this thread cannot access group
* @throws IllegalThreadStateException if group is destroyed
* @since 1.4
*/
public Thread (ThreadGroup g, Runnable r, String n, long size)
{
// Just ignore stackSize for now.
this (currentThread (), g, r, n);
}
private Thread (Thread current, ThreadGroup g, Runnable r, String n)
{
// The Class Libraries book says ``threadName cannot be null''. I
// take this to mean NullPointerException.
if (n == null)
throw new NullPointerException ();
if (g == null)
{
// If CURRENT is null, then we are bootstrapping the first thread.
// Use ThreadGroup.root, the main threadgroup.
if (current == null)
group = ThreadGroup.root;
else
group = current.getThreadGroup();
}
else
group = g;
data = null;
interrupt_flag = false;
alive_flag = false;
startable_flag = true;
if (current != null)
{
group.checkAccess();
daemon_flag = current.isDaemon();
int gmax = group.getMaxPriority();
int pri = current.getPriority();
priority = (gmax < pri ? gmax : pri);
context_class_loader = current.context_class_loader;
InheritableThreadLocal.newChildThread(this);
}
else
{
daemon_flag = false;
priority = NORM_PRIORITY;
}
name = n;
group.addThread(this);
runnable = r;
initialize_native ();
}
/**
* Allocates a new Thread object. This constructor has
* the same effect as Thread(null, null,
* gname), where gname is
* a newly generated name. Automatically generated names are of the
* form "Thread-"+n, where n is an integer.
* run() method to actually do anything. An example
* illustrating this method being used follows:
*
*
* @see java.lang.Thread#Thread(java.lang.ThreadGroup,
* java.lang.Runnable, java.lang.String)
*/
public Thread ()
{
this (null, null, gen_name ());
}
/**
* Allocates a new
* import java.lang.*;
*
* class plain01 implements Runnable {
* String name;
* plain01() {
* name = null;
* }
* plain01(String s) {
* name = s;
* }
* public void run() {
* if (name == null)
* System.out.println("A new thread created");
* else
* System.out.println("A new thread with name " + name +
* " created");
* }
* }
* class threadtest01 {
* public static void main(String args[] ) {
* int failed = 0 ;
*
* Thread t1 = new Thread();
* if (t1 != null)
* System.out.println("new Thread() succeed");
* else {
* System.out.println("new Thread() failed");
* failed++;
* }
* }
* }
* Thread object. This constructor has
* the same effect as Thread(null, target,
* gname), where gname is
* a newly generated name. Automatically generated names are of the
* form "Thread-"+n, where n is an integer.
*
* @param target the object whose run method is called.
* @see java.lang.Thread#Thread(java.lang.ThreadGroup,
* java.lang.Runnable, java.lang.String)
*/
public Thread (Runnable r)
{
this (null, r, gen_name ());
}
/**
* Allocates a new Thread object. This constructor has
* the same effect as Thread(null, null, name).
*
* @param name the name of the new thread.
* @see java.lang.Thread#Thread(java.lang.ThreadGroup,
* java.lang.Runnable, java.lang.String)
*/
public Thread (String n)
{
this (null, null, n);
}
/**
* Allocates a new Thread object. This constructor has
* the same effect as Thread(group, target,
* gname), where gname is
* a newly generated name. Automatically generated names are of the
* form "Thread-"+n, where n is an integer.
*
* @param group the thread group.
* @param target the object whose run method is called.
* @exception SecurityException if the current thread cannot create a
* thread in the specified thread group.
* @see java.lang.Thread#Thread(java.lang.ThreadGroup,
* java.lang.Runnable, java.lang.String)
*/
public Thread (ThreadGroup g, Runnable r)
{
this (g, r, gen_name ());
}
/**
* Allocates a new Thread object. This constructor has
* the same effect as Thread(group, null, name)
*
* @param group the thread group.
* @param name the name of the new thread.
* @exception SecurityException if the current thread cannot create a
* thread in the specified thread group.
* @see java.lang.Thread#Thread(java.lang.ThreadGroup,
* java.lang.Runnable, java.lang.String)
*/
public Thread (ThreadGroup g, String n)
{
this (g, null, n);
}
/**
* Allocates a new Thread object. This constructor has
* the same effect as Thread(null, target, name).
*
* @param target the object whose run method is called.
* @param name the name of the new thread.
* @see java.lang.Thread#Thread(java.lang.ThreadGroup,
* java.lang.Runnable, java.lang.String)
*/
public Thread (Runnable r, String n)
{
this (null, r, n);
}
/**
* Returns a string representation of this thread, including the
* thread's name, priority, and thread group.
*
* @return a string representation of this thread.
*/
public String toString ()
{
return "Thread[" + name + "," + priority + "," +
(group == null ? "" : group.getName()) + "]";
}
/**
* Causes the currently executing thread object to temporarily pause
* and allow other threads to execute.
*/
public static native void yield ();
// Private data.
ThreadGroup group;
String name;
private Runnable runnable;
private int priority;
private boolean daemon_flag;
boolean interrupt_flag;
private boolean alive_flag;
private boolean startable_flag;
private ClassLoader context_class_loader;
// This describes the top-most interpreter frame for this thread.
RawData interp_frame;
// Our native data - points to an instance of struct natThread.
private Object data;
}