java.lang.management
Interface ThreadMXBean

public interface 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 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(boolean) 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(boolean) method can be used to enable thread contention monitoring.

Since:

1.5

See Also:

JMX Specification., Ways to Access MXBeans

Method Summary

long[]	findMonitorDeadlockedThreads() Finds cycles of threads that are in deadlock waiting to acquire object monitors.
long[]	getAllThreadIds() Returns all live thread IDs.
long	getCurrentThreadCpuTime() Returns the total CPU time for the current thread in nanoseconds.
long	getCurrentThreadUserTime() Returns the CPU time that the current thread has executed in user mode in nanoseconds.
int	getDaemonThreadCount() Returns the current number of live daemon threads.
int	getPeakThreadCount() Returns the peak live thread count since the Java virtual machine started or peak was reset.
int	getThreadCount() Returns the current number of live threads including both daemon and non-daemon threads.
long	getThreadCpuTime(long id) Returns the total CPU time for a thread of the specified ID in nanoseconds.
ThreadInfo	getThreadInfo(long id) Returns the thread info for a thread of the specified id with no stack trace.
ThreadInfo[]	getThreadInfo(long[] ids) Returns the thread info for each thread whose ID is in the input array ids with no stack trace.
ThreadInfo[]	getThreadInfo(long[] ids, int maxDepth) Returns the thread info for each thread whose ID is in the input array ids.
ThreadInfo	getThreadInfo(long id, int maxDepth) Returns a thread info for a thread of the specified id.
long	getThreadUserTime(long id) Returns the CPU time that a thread of the specified ID has executed in user mode in nanoseconds.
long	getTotalStartedThreadCount() Returns the total number of threads created and also started since the Java virtual machine started.
boolean	isCurrentThreadCpuTimeSupported() Tests if the Java virtual machine supports CPU time measurement for the current thread.
boolean	isThreadContentionMonitoringEnabled() Tests if thread contention monitoring is enabled.
boolean	isThreadContentionMonitoringSupported() Tests if the Java virtual machine supports thread contention monitoring.
boolean	isThreadCpuTimeEnabled() Tests if thread CPU time measurement is enabled.
boolean	isThreadCpuTimeSupported() Tests if the Java virtual machine implementation supports CPU time measurement for any thread.
void	resetPeakThreadCount() Resets the peak thread count to the current number of live threads.
void	setThreadContentionMonitoringEnabled(boolean enable) Enables or disables thread contention monitoring.
void	setThreadCpuTimeEnabled(boolean enable) Enables or disables thread CPU time measurement.

Method Detail

getThreadCount

int getThreadCount()

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

Returns:

the current number of live threads.

getPeakThreadCount

int getPeakThreadCount()

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

Returns:

the peak live thread count.

getTotalStartedThreadCount

long getTotalStartedThreadCount()

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

Returns:

the total number of threads started.

getDaemonThreadCount

int getDaemonThreadCount()

Returns the current number of live daemon threads.

Returns:

the current number of live daemon threads.

getAllThreadIds

long[] getAllThreadIds()

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

Returns:

an array of long, each is a thread ID.

Throws:

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

getThreadInfo

ThreadInfo getThreadInfo(long id)

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.

Returns:

a 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.

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

getThreadInfo

ThreadInfo[] getThreadInfo(long[] ids)

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

Returns:

an array of the 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.

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

getThreadInfo

ThreadInfo getThreadInfo(long id,
                         int maxDepth)

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.

Returns:

a 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.

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

getThreadInfo

ThreadInfo[] getThreadInfo(long[] ids,
                           int maxDepth)

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.

Returns:

an array of the 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.

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

isThreadContentionMonitoringSupported

boolean isThreadContentionMonitoringSupported()

Tests if the Java virtual machine supports thread contention monitoring.

Returns:

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

isThreadContentionMonitoringEnabled

boolean isThreadContentionMonitoringEnabled()

Tests if thread contention monitoring is enabled.

Returns:

true if thread contention monitoring is enabled; false otherwise.

Throws:

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

See Also:

isThreadContentionMonitoringSupported()

setThreadContentionMonitoringEnabled

void setThreadContentionMonitoringEnabled(boolean enable)

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

Parameters:

enable - true to enable; false to disable.

Throws:

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

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

See Also:

isThreadContentionMonitoringSupported()

getCurrentThreadCpuTime

long getCurrentThreadCpuTime()

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());
 

Returns:

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

Throws:

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

See Also:

getCurrentThreadUserTime(), isCurrentThreadCpuTimeSupported(), isThreadCpuTimeEnabled(), setThreadCpuTimeEnabled(boolean)

getCurrentThreadUserTime

long getCurrentThreadUserTime()

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());
 

Returns:

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

Throws:

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

See Also:

getCurrentThreadCpuTime(), isCurrentThreadCpuTimeSupported(), isThreadCpuTimeEnabled(), setThreadCpuTimeEnabled(boolean)

getThreadCpuTime

long getThreadCpuTime(long id)

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

Returns:

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 .

UnsupportedOperationException - if the Java virtual machine does not support CPU time measurement for other threads.

See Also:

getThreadUserTime(long), isThreadCpuTimeSupported(), isThreadCpuTimeEnabled(), setThreadCpuTimeEnabled(boolean)

getThreadUserTime

long getThreadUserTime(long id)

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.

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

Returns:

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 .

UnsupportedOperationException - if the Java virtual machine does not support CPU time measurement for other threads.

See Also:

getThreadCpuTime(long), isThreadCpuTimeSupported(), isThreadCpuTimeEnabled(), setThreadCpuTimeEnabled(boolean)

isThreadCpuTimeSupported

boolean isThreadCpuTimeSupported()

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.

Returns:

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

isCurrentThreadCpuTimeSupported

boolean isCurrentThreadCpuTimeSupported()

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

Returns:

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

isThreadCpuTimeEnabled

boolean isThreadCpuTimeEnabled()

Tests if thread CPU time measurement is enabled.

Returns:

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

Throws:

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

See Also:

isThreadCpuTimeSupported(), isCurrentThreadCpuTimeSupported()

setThreadCpuTimeEnabled

void setThreadCpuTimeEnabled(boolean enable)

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

Parameters:

enable - true to enable; false to disable.

Throws:

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

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

See Also:

isThreadCpuTimeSupported(), isCurrentThreadCpuTimeSupported()

findMonitorDeadlockedThreads

long[] findMonitorDeadlockedThreads()

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.

Returns:

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

Throws:

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

resetPeakThreadCount

void resetPeakThreadCount()

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

Throws:

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

See Also:

getPeakThreadCount(), getThreadCount()