Every thread has a priority. Threads with higher priority are executed in preference to threads with lower priority. Each thread may or may not also be marked as a daemon. When code running in some thread creates a new Thread object, the new thread has its priority initially set equal to the priority of the creating thread, and is a daemon thread if and only if the creating thread is a daemon.
When a Java Virtual Machine starts up, there is usually a single non-daemon thread (which typically calls the method named main of some designated class). The Java Virtual Machine continues to execute threads until either of the following occurs:
exit method of class Runtime has been called and the security manager has permitted the exit operation to take place. run method or by throwing an exception that propagates beyond the run method. There are two ways to create a new thread of execution. One is to declare a class to be a subclass of Thread. This subclass should override the run method of class Thread. An instance of the subclass can then be allocated and started. For example, a thread that computes primes larger than a stated value could be written as follows:
class PrimeThread extends Thread {
long minPrime;
PrimeThread(long minPrime) {
this.minPrime = minPrime;
}
public void run() {
// compute primes larger than minPrime
. . .
}
}
The following code would then create a thread and start it running:
PrimeThread p = new PrimeThread(143); p.start();
The other way to create a thread is to declare a class that implements the Runnable interface. That class then implements the run method. An instance of the class can then be allocated, passed as an argument when creating Thread, and started. The same example in this other style looks like the following:
class PrimeRun implements Runnable {
long minPrime;
PrimeRun(long minPrime) {
this.minPrime = minPrime;
}
public void run() {
// compute primes larger than minPrime
. . .
}
}
The following code would then create a thread and start it running:
PrimeRun p = new PrimeRun(143); new Thread(p).start();
Every thread has a name for identification purposes. More than one thread may have the same name. If a name is not specified when a thread is created, a new name is generated for it.
| Field Detail |
public static final int MIN_PRIORITY
public static final int NORM_PRIORITY
public static final int MAX_PRIORITY
| Constructor Detail |
public Thread()
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.public Thread(java.lang.Runnable target)
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.target - the object whose run method is called.
public Thread(java.lang.ThreadGroup group,
java.lang.Runnable target)
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.group - the thread group.target - the object whose run method is called.SecurityException - if the current thread cannot create a thread in the specified thread group.public Thread(java.lang.String name)
Thread object. This constructor has the same effect as Thread(null, null, name).name - the name of the new thread.
public Thread(java.lang.ThreadGroup group,
java.lang.String name)
Thread object. This constructor has the same effect as Thread(group, null, name)group - the thread group.name - the name of the new thread.SecurityException - if the current thread cannot create a thread in the specified thread group.
public Thread(java.lang.Runnable target,
java.lang.String name)
Thread object. This constructor has the same effect as Thread(null, target, name).target - the object whose run method is called.name - the name of the new thread.
public Thread(java.lang.ThreadGroup group,
java.lang.Runnable target,
java.lang.String name)
Thread object so that it has target as its run object, has the specified name as its name, and belongs to the thread group referred to by group. If group is null and there is a security manager, the group is determined by the security manager's getThreadGroup method. If group is null and there is not a security manager, or the security manager's getThreadGroup method returns null, the group is set to be the same ThreadGroup as the thread that is creating the new thread.
If there is a security manager, its checkAccess method is called with the ThreadGroup as its argument. This may result in a SecurityException.
If the target argument is not null, the run method of the target is called when this thread is started. If the target argument is null, this thread's run method is called when this thread is started.
The priority of the newly created thread is set equal to the priority of the thread creating it, that is, the currently running thread. The method setPriority may be used to change the priority to a new value.
The newly created thread is initially marked as being a daemon thread if and only if the thread creating it is currently marked as a daemon thread. The method setDaemon may be used to change whether or not a thread is a daemon.
group - the thread group.target - the object whose run method is called.name - the name of the new thread.SecurityException - if the current thread cannot create a thread in the specified thread group.
public Thread(java.lang.ThreadGroup group,
java.lang.Runnable target,
java.lang.String name,
long stackSize)
Thread object so that it has target as its run object, has the specified name as its name, belongs to the thread group referred to by group, and has the specified stack size. This constructor is identical to #Thread(ThreadGroup,Runnable,String) with the exception of the fact that it allows the thread stack size to be specified. 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 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.
group - the thread group.target - the object whose run method is called.name - the name of the new thread.stackSize - the desired stack size for the new thread, or zero to indicate that this parameter is to be ignored.SecurityException - if the current thread cannot create a thread in the specified thread group.| Method Detail |
public static native java.lang.Thread currentThread()
public static native void yield()
public static native void sleep(long millis)
millis - the length of time to sleep in milliseconds.InterruptedException - if another thread has interrupted the current thread. The interrupted status of the current thread is cleared when this exception is thrown.
public static void sleep(long millis,
int nanos)
millis - the length of time to sleep in milliseconds.nanos - 0-999999 additional nanoseconds to sleep.IllegalArgumentException - if the value of millis is negative or the value of nanos is not in the range 0-999999.InterruptedException - if another thread has interrupted the current thread. The interrupted status of the current thread is cleared when this exception is thrown.
private void init(java.lang.ThreadGroup g,
java.lang.Runnable target,
java.lang.String name,
long stackSize)
g - the Thread grouptarget - the object whose run() method gets calledname - the name of the new ThreadstackSize - the desired stack size for the new thread, or zero to indicate that this parameter is to be ignored.public native synchronized void start()
run method of this thread. The result is that two threads are running concurrently: the current thread (which returns from the call to the start method) and the other thread (which executes its run method).
IllegalThreadStateException - if the thread was already started.public void run()
Runnable run object, then that Runnable object's run method is called; otherwise, this method does nothing and returns. Subclasses of Thread should override this method.
private void exit()
public final void stop()
ThreadDeath exception propagating up the stack). If any of the objects previously protected by these monitors were in an inconsistent state, the damaged objects become visible to other threads, potentially resulting in arbitrary behavior. Many uses of stop should be replaced by code that simply modifies some variable to indicate that the target thread should stop running. The target thread should check this variable regularly, and return from its run method in an orderly fashion if the variable indicates that it is to stop running. If the target thread waits for long periods (on a condition variable, for example), the interrupt method should be used to interrupt the wait. For more information, see Why are Thread.stop, Thread.suspend and Thread.resume Deprecated?. If there is a security manager installed, its checkAccess method is called with this as its argument. This may result in a SecurityException being raised (in the current thread).
If this thread is different from the current thread (that is, the current thread is trying to stop a thread other than itself), the security manager's checkPermission method (with a RuntimePermission("stopThread") argument) is called in addition. Again, this may result in throwing a SecurityException (in the current thread).
The thread represented by this thread is forced to stop whatever it is doing abnormally and to throw a newly created ThreadDeath object as an exception.
It is permitted to stop a thread that has not yet been started. If the thread is eventually started, it immediately terminates.
An application should not normally try to catch ThreadDeath unless it must do some extraordinary cleanup operation (note that the throwing of ThreadDeath causes finally clauses of try statements to be executed before the thread officially dies). If a catch clause catches a ThreadDeath object, it is important to rethrow the object so that the thread actually dies.
The top-level error handler that reacts to otherwise uncaught exceptions does not print out a message or otherwise notify the application if the uncaught exception is an instance of ThreadDeath.
SecurityException - if the current thread cannot modify this thread.public final synchronized void stop(java.lang.Throwable obj)
If there is a security manager installed, the checkAccess method of this thread is called, which may result in a SecurityException being raised (in the current thread).
If this thread is different from the current thread (that is, the current thread is trying to stop a thread other than itself) or obj is not an instance of ThreadDeath, the security manager's checkPermission method (with the RuntimePermission("stopThread") argument) is called in addition. Again, this may result in throwing a SecurityException (in the current thread).
If the argument obj is null, a NullPointerException is thrown (in the current thread).
The thread represented by this thread is forced to complete whatever it is doing abnormally and to throw the Throwable object obj as an exception. This is an unusual action to take; normally, the stop method that takes no arguments should be used.
It is permitted to stop a thread that has not yet been started. If the thread is eventually started, it immediately terminates.
obj - the Throwable object to be thrown.SecurityException - if the current thread cannot modify this thread.public void interrupt()
First the checkAccess method of this thread is invoked, which may cause a SecurityException to be thrown.
If this thread is blocked in an invocation of the wait(), wait(long), or int) wait(long, int) methods of the Object class, or of the #join(), #join(long), int), #sleep(long), or int), methods of this class, then its interrupt status will be cleared and it will receive an InterruptedException.
If this thread is blocked in an I/O operation upon an interruptible channel then the channel will be closed, the thread's interrupt status will be set, and the thread will receive a java.nio.channels.ClosedByInterruptException.
If this thread is blocked in a java.nio.channels.Selector then the thread's interrupt status will be set and it will return immediately from the selection operation, possibly with a non-zero value, just as if the selector's wakeup method were invoked.
If none of the previous conditions hold then this thread's interrupt status will be set.
SecurityException - if the current thread cannot modify this threadpublic static boolean interrupted()
true if the current thread has been interrupted; false otherwise.public boolean isInterrupted()
true if this thread has been interrupted; false otherwise.private native boolean isInterrupted(boolean ClearInterrupted)
public void destroy()
public final native boolean isAlive()
true if this thread is alive; false otherwise.public final void suspend()
resume, deadlock results. Such deadlocks typically manifest themselves as "frozen" processes. For more information, see Why are Thread.stop, Thread.suspend and Thread.resume Deprecated?. First, the checkAccess method of this thread is called with no arguments. This may result in throwing a SecurityException (in the current thread).
If the thread is alive, it is suspended and makes no further progress unless and until it is resumed.
SecurityException - if the current thread cannot modify this thread.public final void resume()
First, the checkAccess method of this thread is called with no arguments. This may result in throwing a SecurityException (in the current thread).
If the thread is alive but suspended, it is resumed and is permitted to make progress in its execution.
SecurityException - if the current thread cannot modify this thread.public final void setPriority(int newPriority)
First the checkAccess method of this thread is called with no arguments. This may result in throwing a SecurityException.
Otherwise, the priority of this thread is set to the smaller of the specified newPriority and the maximum permitted priority of the thread's thread group.
newPriority - priority to set this thread toIllegalArgumentException - If the priority is not in the range MIN_PRIORITY to MAX_PRIORITY.SecurityException - if the current thread cannot modify this thread.public final int getPriority()
public final void setName(java.lang.String name)
name. First the checkAccess method of this thread is called with no arguments. This may result in throwing a SecurityException.
name - the new name for this thread.SecurityException - if the current thread cannot modify this thread.public final java.lang.String getName()
public final java.lang.ThreadGroup getThreadGroup()
public static int activeCount()
public static int enumerate(java.lang.Thread[] tarray)
enumerate method of the current thread's thread group with the array argument. First, if there is a security manager, that enumerate method calls the security manager's checkAccess method with the thread group as its argument. This may result in throwing a SecurityException.
tarray - an array of Thread objects to copy toSecurityException - if a security manager exists and its checkAccess method doesn't allow the operation.public native int countStackFrames()
IllegalThreadStateException - if this thread is not suspended.public final synchronized void join(long millis)
millis milliseconds for this thread to die. A timeout of 0 means to wait forever.millis - the time to wait in milliseconds.InterruptedException - if another thread has interrupted the current thread. The interrupted status of the current thread is cleared when this exception is thrown.
public final synchronized void join(long millis,
int nanos)
millis milliseconds plus nanos nanoseconds for this thread to die.millis - the time to wait in milliseconds.nanos - 0-999999 additional nanoseconds to wait.IllegalArgumentException - if the value of millis is negative the value of nanos is not in the range 0-999999.InterruptedException - if another thread has interrupted the current thread. The interrupted status of the current thread is cleared when this exception is thrown.public final void join()
InterruptedException - if another thread has interrupted the current thread. The interrupted status of the current thread is cleared when this exception is thrown.public static void dumpStack()
public final void setDaemon(boolean on)
This method must be called before the thread is started.
This method first calls the checkAccess method of this thread with no arguments. This may result in throwing a SecurityException (in the current thread).
on - if true, marks this thread as a daemon thread.IllegalThreadStateException - if this thread is active.SecurityException - if the current thread cannot modify this thread.public final boolean isDaemon()
true if this thread is a daemon thread; false otherwise.public final void checkAccess()
If there is a security manager, its checkAccess method is called with this thread as its argument. This may result in throwing a SecurityException.
Note: This method was mistakenly non-final in JDK 1.1. It has been made final in the Java 2 Platform.
SecurityException - if the current thread is not allowed to access this thread.public java.lang.String toString()
public java.lang.ClassLoader getContextClassLoader()
First, if there is a security manager, and the caller's class loader is not null and the caller's class loader is not the same as or an ancestor of the context class loader for the thread whose context class loader is being requested, then the security manager's checkPermission method is called with a RuntimePermission("getClassLoader") permission to see if it's ok to get the context ClassLoader..
SecurityException - if a security manager exists and its checkPermission method doesn't allow getting the context ClassLoader.public void setContextClassLoader(java.lang.ClassLoader cl)
First, if there is a security manager, its checkPermission method is called with a RuntimePermission("setContextClassLoader") permission to see if it's ok to set the context ClassLoader..
cl - the context ClassLoader for this ThreadSecurityException - if the current thread cannot set the context ClassLoader.public static native boolean holdsLock(java.lang.Object obj)
This method is designed to allow a program to assert that the current thread already holds a specified lock:
assert Thread.holdsLock(obj);
obj - the object on which to test lock ownershipNullPointerException - if obj is null