java.lang.management.ThreadMXBean

The management interface for the thread system of the Java virtual machine.

A Java virtual machine has a single instance of the implementation class of this interface. This instance implementing this interface is an MXBean that can be obtained by calling the ManagementFactory#getThreadMXBean method or from the platform MBeanServer method.

The ObjectName for uniquely identifying the MXBean for the thread system within an MBeanServer is:

java.lang:type=Threading

Thread ID

Thread ID is a positive long value returned by calling the java.lang.Thread#getId method for a thread. The thread ID is unique during its lifetime. When a thread is terminated, this thread ID may be reused.

Some methods in this interface take a thread ID or an array of thread IDs as the input parameter and return per-thread information.

Thread CPU time

A Java virtual machine implementation may support measuring the CPU time for the current thread, for any thread, or for no threads.

The #isThreadCpuTimeSupported method can be used to determine if a Java virtual machine supports measuring of the CPU time for any thread. The #isCurrentThreadCpuTimeSupported method can be used to determine if a Java virtual machine supports measuring of the CPU time for the current thread. A Java virtual machine implementation that supports CPU time measurement for any thread will also support that for the current thread.

The CPU time provided by this interface has nanosecond precision but not necessarily nanosecond accuracy.

A Java virtual machine may disable CPU time measurement by default. The #isThreadCpuTimeEnabled and #setThreadCpuTimeEnabled methods can be used to test if CPU time measurement is enabled and to enable/disable this support respectively. Enabling thread CPU measurement could be expensive in some Java virtual machine implementations.

Thread Contention Monitoring

Some Java virtual machines may support thread contention monitoring. The #isThreadContentionMonitoringSupported method can be used to determine if a Java virtual machine supports thread contention monitoring. The thread contention monitoring is disabled by default. The #setThreadContentionMonitoringEnabled method can be used to enable thread contention monitoring.

@author

Mandy Chung

@version

1.14, 04/29/04

@since

1.5

Finds cycles of threads that are in deadlock waiting to acquire object monitors. That is, threads that are blocked waiting to enter a synchronization block or waiting to reenter a synchronization block after an Object.wait call, where each thread owns one monitor while trying to obtain another monitor already held by another thread in a cycle.

More formally, a thread is monitor deadlocked if it is part of a cycle in the relation "is waiting for an object monitor owned by". In the simplest case, thread A is blocked waiting for a monitor owned by thread B, and thread B is blocked waiting for a monitor owned by thread A.

This method is designed for troubleshooting use, but not for synchronization control. It might be an expensive operation.

Return

an array of IDs of the threads that are monitor deadlocked, if any; null otherwise.

Throws

java.lang.SecurityException

if a security manager exists and the caller does not have ManagementPermission("monitor").

Returns all live thread IDs. Some threads included in the returned array may have been terminated when this method returns.

Return

an array of long, each is a thread ID.

Throws

java.lang.SecurityException

if a security manager exists and the caller does not have ManagementPermission("monitor").

Returns the total CPU time for the current thread in nanoseconds. The returned value is of nanoseconds precison but not necessarily nanoseconds accuracy. If the implementation distinguishes between user mode time and system mode time, the returned CPU time is the amount of time that the current thread has executed in user mode or system mode.

This is a convenient method for local management use and is equivalent to calling:

   getThreadCpuTime
(Thread.currentThread().getId());

Return

the total CPU time for the current thread if CPU time measurement is enabled; -1 otherwise.

Throws

java.lang.UnsupportedOperationException

if the Java virtual machine does not support CPU time measurement for the current thread.

Returns the CPU time that the current thread has executed in user mode in nanoseconds. The returned value is of nanoseconds precison but not necessarily nanoseconds accuracy.

This is a convenient method for local management use and is equivalent to calling:

   getThreadUserTime
(Thread.currentThread().getId());

Return

the user-level CPU time for the current thread if CPU time measurement is enabled; -1 otherwise.

Throws

java.lang.UnsupportedOperationException

if the Java virtual machine does not support CPU time measurement for the current thread.

Returns the current number of live daemon threads.

Return

the current number of live daemon threads.

Returns the peak live thread count since the Java virtual machine started or peak was reset.

Return

the peak live thread count.

Returns the current number of live threads including both daemon and non-daemon threads.

Return

the current number of live threads.

Returns the total CPU time for a thread of the specified ID in nanoseconds. The returned value is of nanoseconds precision but not necessarily nanoseconds accuracy. If the implementation distinguishes between user mode time and system mode time, the returned CPU time is the amount of time that the thread has executed in user mode or system mode.

If the thread of the specified ID is not alive or does not exist, this method returns -1. If CPU time measurement is disabled, this method returns -1. A thread is alive if it has been started and has not yet died.

If CPU time measurement is enabled after the thread has started, the Java virtual machine implementation may choose any time up to and including the time that the capability is enabled as the point where CPU time measurement starts.

Parameters

id	the thread ID of a thread

Return

the total CPU time for a thread of the specified ID if the thread of the specified ID exists, the thread is alive, and CPU time measurement is enabled; -1 otherwise.

Throws

IllegalArgumentException	if `id <= 0` .
java.lang.UnsupportedOperationException	if the Java virtual machine does not support CPU time measurement for other threads.

Returns the thread info for a thread of the specified id with no stack trace. This method is equivalent to calling:

getThreadInfo(id, 0);

This method returns a ThreadInfo object representing the thread information for the thread of the specified ID. The stack trace in the returned ThreadInfo object will be an empty array of StackTraceElement. If a thread of the given ID is not alive or does not exist, this method will return null. A thread is alive if it has been started and has not yet died.

MBeanServer access:
The mapped type of ThreadInfo is CompositeData with attributes as specified in ThreadInfo .

Parameters

id	the thread ID of the thread. Must be positive.

Return

a {@link ThreadInfo} object for the thread of the given ID with no stack trace; null if the thread of the given ID is not alive or it does not exist.

Throws

IllegalArgumentException	if `id <= 0`.
java.lang.SecurityException	if a security manager exists and the caller does not have ManagementPermission("monitor").

Returns the thread info for each thread whose ID is in the input array ids with no stack trace. This method is equivalent to calling:

   getThreadInfo
(ids, 0);

This method returns an array of the ThreadInfo objects. The stack trace in each ThreadInfo object will be an empty array of StackTraceElement. If a thread of a given ID is not alive or does not exist, the corresponding element in the returned array will contain null. A thread is alive if it has been started and has not yet died.

MBeanServer access:
The mapped type of ThreadInfo is CompositeData with attributes as specified in ThreadInfo .

Parameters

ids	an array of thread IDs

Return

an array of the {@link ThreadInfo} objects, each containing information about a thread whose ID is in the corresponding element of the input array of IDs.

Throws

IllegalArgumentException	if any element in the input array `ids` is `<= 0`.
java.lang.SecurityException	if a security manager exists and the caller does not have ManagementPermission("monitor").

Returns the thread info for each thread whose ID is in the input array ids. The maxDepth parameter indicates the maximum number of StackTraceElement to be retrieved from the stack trace. If maxDepth == Integer.MAX_VALUE, the entire stack trace of the thread will be dumped. If maxDepth == 0, no stack trace of the thread will be dumped.

When the Java virtual machine has no stack trace information about a thread or maxDepth == 0, the stack trace in the ThreadInfo object will be an empty array of StackTraceElement.

This method returns an array of the ThreadInfo objects, each is the thread information about the thread with the same index as in the ids array. If a thread of the given ID is not alive or does not exist, null will be set in the corresponding element in the returned array. A thread is alive if it has been started and has not yet died.

MBeanServer access:
The mapped type of ThreadInfo is CompositeData with attributes as specified in ThreadInfo .

Parameters

ids	an array of thread IDs
maxDepth	the maximum number of entries in the stack trace to be dumped. `Integer.MAX_VALUE` could be used to request the entire stack to be dumped.

Return

an array of the {@link ThreadInfo} objects, each containing information about a thread whose ID is in the corresponding element of the input array of IDs.

Throws

IllegalArgumentException	if `maxDepth is negative`.
IllegalArgumentException	if any element in the input array `ids` is `<= 0`.
java.lang.SecurityException	if a security manager exists and the caller does not have ManagementPermission("monitor").

Returns a thread info for a thread of the specified id. The maxDepth parameter indicates the maximum number of StackTraceElement to be retrieved from the stack trace. If maxDepth == Integer.MAX_VALUE, the entire stack trace of the thread will be dumped. If maxDepth == 0, no stack trace of the thread will be dumped.

When the Java virtual machine has no stack trace information about a thread or maxDepth == 0, the stack trace in the ThreadInfo object will be an empty array of StackTraceElement.

If a thread of the given ID is not alive or does not exist, this method will return null. A thread is alive if it has been started and has not yet died.

MBeanServer access:
The mapped type of ThreadInfo is CompositeData with attributes as specified in ThreadInfo .

Parameters

id	the thread ID of the thread. Must be positive.
maxDepth	the maximum number of entries in the stack trace to be dumped. `Integer.MAX_VALUE` could be used to request the entire stack to be dumped.

Return

a {@link ThreadInfo} of the thread of the given ID. null if the thread of the given ID is not alive or it does not exist.

Throws

IllegalArgumentException	if `id <= 0`.
IllegalArgumentException	if `maxDepth is negative`.
java.lang.SecurityException	if a security manager exists and the caller does not have ManagementPermission("monitor").

Returns the CPU time that a thread of the specified ID has executed in user mode in nanoseconds. The returned value is of nanoseconds precision but not necessarily nanoseconds accuracy.

Parameters

id	the thread ID of a thread

Return

the user-level CPU time for a thread of the specified ID if the thread of the specified ID exists, the thread is alive, and CPU time measurement is enabled; -1 otherwise.

Throws

IllegalArgumentException	if `id <= 0` .
java.lang.UnsupportedOperationException	if the Java virtual machine does not support CPU time measurement for other threads.

Returns the total number of threads created and also started since the Java virtual machine started.

Return

the total number of threads started.

Tests if the Java virtual machine supports CPU time measurement for the current thread. This method returns true if #isThreadCpuTimeSupported returns true.

Return

true if the Java virtual machine supports CPU time measurement for current thread; false otherwise.

Tests if thread contention monitoring is enabled.

Return

true if thread contention monitoring is enabled; false otherwise.

Throws

java.lang.UnsupportedOperationException

if the Java virtual machine does not support thread contention monitoring.

See Also

#isThreadContentionMonitoringSupported

Tests if the Java virtual machine supports thread contention monitoring.

Return

true if the Java virtual machine supports thread contention monitoring; false otherwise.

Tests if thread CPU time measurement is enabled.

Return

true if thread CPU time measurement is enabled; false otherwise.

Throws

java.lang.UnsupportedOperationException

if the Java virtual machine does not support CPU time measurement for other threads nor for the current thread.

Tests if the Java virtual machine implementation supports CPU time measurement for any thread. A Java virtual machine implementation that supports CPU time measurement for any thread will also support CPU time measurement for the current thread.

Return

true if the Java virtual machine supports CPU time measurement for any thread; false otherwise.

Resets the peak thread count to the current number of live threads.

Throws

java.lang.SecurityException

if a security manager exists and the caller does not have ManagementPermission("control").

See Also

#getPeakThreadCount , #getThreadCount

Enables or disables thread contention monitoring. Thread contention monitoring is disabled by default.

Parameters

enable true to enable; false to disable.

Throws

java.lang.UnsupportedOperationException	if the Java virtual machine does not support thread contention monitoring.
java.lang.SecurityException	if a security manager exists and the caller does not have ManagementPermission("control").

See Also

#isThreadContentionMonitoringSupported

Enables or disables thread CPU time measurement. The default is platform dependent.

Parameters

enable true to enable; false to disable.

Throws

java.lang.UnsupportedOperationException	if the Java virtual machine does not support CPU time measurement for any threads nor for the current thread.
java.lang.SecurityException	if a security manager exists and the caller does not have ManagementPermission("control").