juce::Thread Class Reference

Encapsulates a thread. More...

#include <juce_Thread.h>

Inheritance diagram for juce::Thread:

Collaboration diagram for juce::Thread:

Classes
class	Listener
	Used to receive callbacks for thread exit calls. More...

Public Types
enum	{ realtimeAudioPriority = -1 }
	Special realtime audio thread priority. More...
using	ThreadID = void *
	A value type used for thread IDs. More...

Public Member Functions
	Thread (const String &threadName, size_t threadStackSize=0)
	Creates a thread. More...
virtual	~Thread ()
	Destructor. More...
void	addListener (Listener *)
	Add a listener to this thread which will receive a callback when signalThreadShouldExit was called on this thread. More...
ThreadID	getThreadId () const noexcept
	Returns the ID of this thread. More...
const String &	getThreadName () const noexcept
	Returns the name of the thread. More...
bool	isThreadRunning () const
	Returns true if the thread is currently active. More...
void	notify () const
	Wakes up the thread. More...
void	removeListener (Listener *)
	Removes a listener added with addListener. More...
virtual void	run ()=0
	Must be implemented to perform the thread's actual code. More...
void	setAffinityMask (uint32 affinityMask)
	Sets the affinity mask for the thread. More...
bool	setPriority (int priority)
	Changes the thread's priority. More...
void	signalThreadShouldExit ()
	Sets a flag to tell the thread it should stop. More...
void	startThread ()
	Starts the thread running. More...
void	startThread (int priority)
	Starts the thread with a given priority. More...
bool	stopThread (int timeOutMilliseconds)
	Attempts to stop the thread running. More...
bool	threadShouldExit () const
	Checks whether the thread has been told to stop running. More...
bool	wait (int timeOutMilliseconds) const
	Suspends the execution of this thread until either the specified timeout period has elapsed, or another thread calls the notify() method to wake it up. More...
bool	waitForThreadToExit (int timeOutMilliseconds) const
	Waits for the thread to stop. More...

Static Public Member Functions
static bool	currentThreadShouldExit ()
	Checks whether the current thread has been told to stop running. More...
static Thread *	getCurrentThread ()
	Finds the thread object that is currently running. More...
static ThreadID	getCurrentThreadId ()
	Returns an id that identifies the caller thread. More...
static void	initialiseJUCE (void *jniEnv, void *jContext)
	Initialises the JUCE subsystem for projects not created by the Projucer. More...
static void	launch (std::function< void()> functionToRun)
	Invokes a lambda or function on its own thread. More...
static void	setCurrentThreadAffinityMask (uint32 affinityMask)
	Changes the affinity mask for the caller thread. More...
static void	setCurrentThreadName (const String &newThreadName)
	Changes the name of the caller thread. More...
static bool	setCurrentThreadPriority (int priority)
	Changes the priority of the caller thread. More...
static void	sleep (int milliseconds)
	Suspends the execution of the current thread until the specified timeout period has elapsed (note that this may not be exact). More...
static void	yield ()
	Yields the current thread's CPU time-slot and allows a new thread to run. More...

Private Member Functions
void	closeThreadHandle ()
void	killThread ()
void	launchThread ()
void	threadEntryPoint ()

Static Private Member Functions
static int	getAdjustedPriority (int)
static bool	setThreadPriority (void *, int)

Private Attributes
uint32	affinityMask = 0
WaitableEvent	defaultEvent
bool	deleteOnThreadEnd = false
bool	isAndroidRealtimeThread = false
ListenerList< Listener, Array< Listener *, CriticalSection > >	listeners
Atomic< int32 >	shouldExit { 0 }
CriticalSection	startStopLock
WaitableEvent	startSuspensionEvent
Atomic< void * >	threadHandle { nullptr }
Atomic< ThreadID >	threadId = {}
const String	threadName
int	threadPriority = 5
size_t	threadStackSize

Detailed Description

Encapsulates a thread.

Subclasses derive from Thread and implement the run() method, in which they do their business. The thread can then be started with the startThread() method and controlled with various other methods.

This class also contains some thread-related static methods, such as sleep(), yield(), getCurrentThreadId() etc.

See also

CriticalSection, WaitableEvent, Process, ThreadWithProgressWindow, MessageManagerLock

@tags{Core}

Member Typedef Documentation

ThreadID

using juce::Thread::ThreadID = void*

A value type used for thread IDs.

See also

getCurrentThreadId(), getThreadId()

Member Enumeration Documentation

anonymous enum

anonymous enum

Special realtime audio thread priority.

This priority will create a high-priority thread which is best suited for realtime audio processing.

Currently, this priority is identical to priority 9, except when building for Android with OpenSL/Oboe support.

In this case, JUCE will ask OpenSL/Oboe to construct a super high priority thread specifically for realtime audio processing.

Note that this priority can only be set before the thread has started. Switching to this priority, or from this priority to a different priority, is not supported under Android and will assert.

For best performance this thread should yield at regular intervals and not call any blocking APIs.

See also

startThread, setPriority, sleep, WaitableEvent

Enumerator
realtimeAudioPriority

Constructor & Destructor Documentation

Thread()

juce::Thread::Thread ( const String &  threadName, size_t  threadStackSize = 0  )

explicit

Creates a thread.

When first created, the thread is not running. Use the startThread() method to start it.

Parameters

threadName	The name of the thread which typically appears in debug logs and profiles.
threadStackSize	The size of the stack of the thread. If this value is zero then the default stack size of the OS will be used.

~Thread()

virtual juce::Thread::~Thread ( )

virtual

Destructor.

You must never attempt to delete a Thread object while it's still running - always call stopThread() and make sure your thread has stopped before deleting the object. Failing to do so will throw an assertion, and put you firmly into undefined behaviour territory.

Member Function Documentation

addListener()

void juce::Thread::addListener

(

Listener *

)

Add a listener to this thread which will receive a callback when signalThreadShouldExit was called on this thread.

See also

signalThreadShouldExit, removeListener

closeThreadHandle()

void juce::Thread::closeThreadHandle ( )

private

References threadHandle, and threadId.

currentThreadShouldExit()

static bool juce::Thread::currentThreadShouldExit ( )

static

Checks whether the current thread has been told to stop running.

On the message thread, this will always return false, otherwise it will return threadShouldExit() called on the current thread.

See also

threadShouldExit

getAdjustedPriority()

static int juce::Thread::getAdjustedPriority ( int  )

staticprivate

getCurrentThread()

static Thread* juce::Thread::getCurrentThread ( )

static

Finds the thread object that is currently running.

Note that the main UI thread (or other non-JUCE threads) don't have a Thread object associated with them, so this will return nullptr.

getCurrentThreadId()

Thread::ThreadID juce::Thread::getCurrentThreadId ( )

static

Returns an id that identifies the caller thread.

To find the ID of a particular thread object, use getThreadId().

Returns

a unique identifier that identifies the calling thread.

See also

getThreadId

Referenced by juce::ThreadLocalValue< Type >::get(), and juce::ThreadLocalValue< Type >::releaseCurrentThreadStorage().

getThreadId()

ThreadID juce::Thread::getThreadId ( ) const

noexcept

Returns the ID of this thread.

That means the ID of this thread object - not of the thread that's calling the method. This can change when the thread is started and stopped, and will be invalid if the thread's not actually running.

See also

getCurrentThreadId

getThreadName()

const String& juce::Thread::getThreadName ( ) const

inlinenoexcept

Returns the name of the thread.

This is the name that gets set in the constructor.

initialiseJUCE()

static void juce::Thread::initialiseJUCE ( void *  jniEnv, void *  jContext  )

static

Initialises the JUCE subsystem for projects not created by the Projucer.

On Android, JUCE needs to be initialised once before it is used. The Projucer will automatically generate the necessary java code to do this. However, if you are using JUCE without the Projucer or are creating a library made with JUCE intended for use in non-JUCE apks, then you must call this method manually once on apk startup.

You can call this method from C++ or directly from java by calling the following java method:

com.rmsl.juce.Java.initialiseJUCE (myContext);

Note that the above java method is only available in Android Studio projects created by the Projucer. If you need to call this from another type of project then you need to add the following java file to your project:

package com.rmsl.juce;
 
public class Java
{
    static { System.loadLibrary ("juce_jni"); }
    public native static void initialiseJUCE (Context context);
}

Parameters

jniEnv	this is a pointer to JNI's JNIEnv variable. Any callback from Java into C++ will have this passed in as it's first parameter.
jContext	this is a jobject referring to your app/service/receiver/ provider's Context. JUCE needs this for many of it's internal functions.

isThreadRunning()

bool juce::Thread::isThreadRunning

(

)

const

Returns true if the thread is currently active.

killThread()

void juce::Thread::killThread ( )

private

References juce::Atomic< Type >::get(), jassertfalse, and threadHandle.

launch()

static void juce::Thread::launch ( std::function< void()>  functionToRun )

static

Invokes a lambda or function on its own thread.

This will spin up a Thread object which calls the function and then exits. Bear in mind that starting and stopping a thread can be a fairly heavyweight operation, so you might prefer to use a ThreadPool if you're kicking off a lot of short background tasks.

Also note that using an anonymous thread makes it very difficult to interrupt the function when you need to stop it, e.g. when your app quits. So it's up to you to deal with situations where the function may fail to stop in time.

launchThread()

void juce::Thread::launchThread ( )

private

References juce::Atomic< Type >::get(), juce::gl::handle, isAndroidRealtimeThread, jassertfalse, juce::threadEntryProc(), threadHandle, threadId, and threadStackSize.

notify()

void juce::Thread::notify

(

)

const

Wakes up the thread.

If the thread has called the wait() method, this will wake it up.

See also

wait

removeListener()

void juce::Thread::removeListener

(

Listener *

)

Removes a listener added with addListener.

run()

virtual void juce::Thread::run ( )

pure virtual

Must be implemented to perform the thread's actual code.

Remember that the thread must regularly check the threadShouldExit() method whilst running, and if this returns true it should return from the run() method as soon as possible to avoid being forcibly killed.

See also

threadShouldExit, startThread

Implemented in juce::MidiOutput, juce::ThreadedAnalyticsDestination::EventDispatcher, juce::NetworkServiceDiscovery::AvailableServiceList, juce::InterprocessConnectionServer, and juce::NetworkServiceDiscovery::Advertiser.

setAffinityMask()

void juce::Thread::setAffinityMask

(

uint32

affinityMask

)

Sets the affinity mask for the thread.

This will only have an effect next time the thread is started - i.e. if the thread is already running when called, it'll have no effect.

See also

setCurrentThreadAffinityMask

setCurrentThreadAffinityMask()

void juce::Thread::setCurrentThreadAffinityMask ( uint32  affinityMask )

static

Changes the affinity mask for the caller thread.

This will change the affinity mask for the thread that calls this static method.

See also

setAffinityMask

References affinityMask, juce::ignoreUnused(), and jassertfalse.

setCurrentThreadName()

void juce::Thread::setCurrentThreadName ( const String &  newThreadName )

static

Changes the name of the caller thread.

Different OSes may place different length or content limits on this name.

References JUCE_AUTORELEASEPOOL, juce::juceStringToNS(), and juce::gl::name.

Referenced by juce::MessageThread::start().

setCurrentThreadPriority()

static bool juce::Thread::setCurrentThreadPriority ( int  priority )

static

Changes the priority of the caller thread.

Similar to setPriority(), but this static method acts on the caller thread. May return false if for some reason the priority can't be changed.

See also

setPriority

Referenced by juce::MessageThread::start().

setPriority()

bool juce::Thread::setPriority

(

int

priority

)

Changes the thread's priority.

May return false if for some reason the priority can't be changed.

Parameters

priority

the new priority, in the range 0 (lowest) to 10 (highest). A priority of 5 is normal.

See also

realtimeAudioPriority

setThreadPriority()

bool juce::Thread::setThreadPriority ( void *  handle, int  priority  )

staticprivate

References juce::gl::handle, juce::jmap(), and juce::gl::param.

signalThreadShouldExit()

void juce::Thread::signalThreadShouldExit

(

)

Sets a flag to tell the thread it should stop.

Calling this means that the threadShouldExit() method will then return true. The thread should be regularly checking this to see whether it should exit.

If your thread makes use of wait(), you might want to call notify() after calling this method, to interrupt any waits that might be in progress, and allow it to reach a point where it can exit.

See also

threadShouldExit, waitForThreadToExit

sleep()

void juce::Thread::sleep ( int  milliseconds )

static

Suspends the execution of the current thread until the specified timeout period has elapsed (note that this may not be exact).

The timeout period must not be negative and whilst sleeping the thread cannot be woken up so it should only be used for short periods of time and when other methods such as using a WaitableEvent or CriticalSection are not possible.

References juce::UnitTestCategories::time.

Referenced by juce::OpenGLContext::NativeContext::initialiseOnRenderThread(), juce::MessageThread::start(), and juce::OpenGLContext::NativeContext::swapBuffers().

startThread() [1/2]

void juce::Thread::startThread

(

)

Starts the thread running.

This will cause the thread's run() method to be called by a new thread. If this thread is already running, startThread() won't do anything.

See also

stopThread

startThread() [2/2]

void juce::Thread::startThread

(

int

priority

)

Starts the thread with a given priority.

Launches the thread with a given priority, where 0 = lowest, 10 = highest. If the thread is already running, its priority will be changed.

See also

startThread, setPriority, realtimeAudioPriority

stopThread()

bool juce::Thread::stopThread

(

int

timeOutMilliseconds

)

Attempts to stop the thread running.

This method will cause the threadShouldExit() method to return true and call notify() in case the thread is currently waiting.

Hopefully the thread will then respond to this by exiting cleanly, and the stopThread method will wait for a given time-period for this to happen.

If the thread is stuck and fails to respond after the timeout, it gets forcibly killed, which is a very bad thing to happen, as it could still be holding locks, etc. which are needed by other parts of your program.

Parameters

timeOutMilliseconds

The number of milliseconds to wait for the thread to finish before killing it by force. A negative value in here will wait forever.

Returns

true if the thread was cleanly stopped before the timeout, or false if it had to be killed by force.

See also

signalThreadShouldExit, threadShouldExit, waitForThreadToExit, isThreadRunning

threadEntryPoint()

void juce::Thread::threadEntryPoint ( )

private

threadShouldExit()

bool juce::Thread::threadShouldExit

(

)

const

Checks whether the thread has been told to stop running.

Threads need to check this regularly, and if it returns true, they should return from their run() method at the first possible opportunity.

See also

signalThreadShouldExit, currentThreadShouldExit

wait()

bool juce::Thread::wait

(

int

timeOutMilliseconds

)

const

Suspends the execution of this thread until either the specified timeout period has elapsed, or another thread calls the notify() method to wake it up.

A negative timeout value means that the method will wait indefinitely.

Returns

true if the event has been signalled, false if the timeout expires.

waitForThreadToExit()

bool juce::Thread::waitForThreadToExit

(

int

timeOutMilliseconds

)

const

Waits for the thread to stop.

This will wait until isThreadRunning() is false or until a timeout expires.

Parameters

timeOutMilliseconds

the time to wait, in milliseconds. If this value is less than zero, it will wait forever.

Returns

true if the thread exits, or false if the timeout expires first.

yield()

void juce::Thread::yield ( )

static

Yields the current thread's CPU time-slot and allows a new thread to run.

If there are no other threads of equal or higher priority currently running then this will return immediately and the current thread will continue to run.

Member Data Documentation

affinityMask

uint32 juce::Thread::affinityMask = 0

private

Referenced by setCurrentThreadAffinityMask().

defaultEvent

WaitableEvent juce::Thread::defaultEvent

private

deleteOnThreadEnd

bool juce::Thread::deleteOnThreadEnd = false

private

isAndroidRealtimeThread

bool juce::Thread::isAndroidRealtimeThread = false

private

Referenced by launchThread().

listeners

ListenerList<Listener, Array<Listener*, CriticalSection> > juce::Thread::listeners

private

shouldExit

Atomic<int32> juce::Thread::shouldExit { 0 }

private

startStopLock

CriticalSection juce::Thread::startStopLock

private

startSuspensionEvent

WaitableEvent juce::Thread::startSuspensionEvent

private

threadHandle

Atomic<void*> juce::Thread::threadHandle { nullptr }

private

Referenced by closeThreadHandle(), killThread(), and launchThread().

threadId

Atomic<ThreadID> juce::Thread::threadId = {}

private

Referenced by closeThreadHandle(), and launchThread().

threadName

const String juce::Thread::threadName

private

threadPriority

int juce::Thread::threadPriority = 5

private

threadStackSize

size_t juce::Thread::threadStackSize

private

Referenced by launchThread().

---

The documentation for this class was generated from the following files:

• juce_Thread.h
• juce_posix_SharedCode.h