PThread Class Reference

#include <thread.h>

Inheritance diagram for PThread:

List of all members.

Construction
enum	Priority {   LowestPriority, LowPriority, NormalPriority, HighPriority,   HighestPriority, NumPriorities }
	Codes for thread priorities. More...
enum	AutoDeleteFlag { AutoDeleteThread, NoAutoDeleteThread }
	Codes for thread autodelete flag. More...
	PThread (PINDEX, AutoDeleteFlag deletion=AutoDeleteThread, Priority priorityLevel=NormalPriority, const PString &threadName=PString::Empty())
	~PThread ()
Control functions
virtual void	Restart ()
virtual void	Terminate ()
virtual PBoolean	IsTerminated () const
void	WaitForTermination () const
PBoolean	WaitForTermination (const PTimeInterval &maxWait) const
virtual void	Suspend (PBoolean susp=PTrue)
virtual void	Resume ()
virtual PBoolean	IsSuspended () const
virtual void	SetPriority (Priority priorityLevel)
virtual Priority	GetPriority () const
virtual void	SetAutoDelete (AutoDeleteFlag deletion=AutoDeleteThread)
void	SetNoAutoDelete ()
virtual PString	GetThreadName () const
virtual void	SetThreadName (const PString &name)
static void	Sleep (const PTimeInterval &delay)
	Suspend the current thread for the specified amount of time.
Miscellaneous
virtual PThreadIdentifier	GetThreadId () const
virtual void	Main ()=0
static PThreadIdentifier	GetCurrentThreadId ()
static PThread *	Current ()
static void	Yield ()
static PThread *	Create (const PNotifier &notifier, INT parameter=0, AutoDeleteFlag deletion=AutoDeleteThread, Priority priorityLevel=NormalPriority, const PString &threadName=PString::Empty(), PINDEX stackSize=65536)
static PThread *	Create (const PNotifier &notifier, const PString &threadName)
Public Member Functions
bool	IsAutoDelete () const
int	PXBlockOnChildTerminate (int pid, const PTimeInterval &timeout)
int	PXBlockOnIO (int handle, int type, const PTimeInterval &timeout)
void	PXAbortBlock () const
Overrides from #PObject
void	PrintOn (ostream &strm) const
Friends
class	PProcess
class	PExternalThread
class	PHouseKeepingThread

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Detailed Description

This class defines a thread of execution in the system. A thread is an independent flow of processor instructions. This differs from a process which also embodies a program address space and resource allocation. So threads can share memory and resources as they run in the context of a given process. A process always contains at least one thread. This is reflected in this library by the PProcess class being descended from the PThread class.

The implementation of a thread is platform dependent, but it is assumed that the platform has some support for native threads. Previous versions of PTLib/PWLib have some support for co-operative threads, but this has been removed.

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Member Enumeration Documentation

enum PThread::AutoDeleteFlag

Codes for thread autodelete flag.

Enumerator:

AutoDeleteThread	Automatically delete thread object on termination.
NoAutoDeleteThread	Don't delete thread as it may not be on heap.

enum PThread::Priority

Codes for thread priorities.

Enumerator:

LowestPriority	Will only run if all other threads are blocked.
LowPriority	Runs approximately half as often as normal.
NormalPriority	Normal priority for a thread.
HighPriority	Runs approximately twice as often as normal.
HighestPriority	Is only thread that will run, unless blocked.
NumPriorities

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Constructor & Destructor Documentation

PThread::PThread	(	PINDEX	,
		AutoDeleteFlag	deletion = AutoDeleteThread,
		Priority	priorityLevel = NormalPriority,
		const PString &	threadName = PString::Empty()
	)

Create a new thread instance. Unless the startSuspended parameter is PTrue, the threads Main() function is called to execute the code for the thread.

Note that the exact timing of the execution of code in threads can never be predicted. Thus you you can get a race condition on intialising a descendent class. To avoid this problem a thread is always started suspended. You must call the Resume() function after your descendent class construction is complete.

If synchronisation is required between threads then the use of semaphores is essential.

If the deletion is set to AutoDeleteThread then the PThread is assumed to be allocated with the new operator and may be freed using the delete operator as soon as the thread is terminated or executes to completion (usually the latter).

The stack size argument retained only for source code compatibility for previous implementations. It is not used in the current code and may be removed in subsequent versions.

Parameters:

deletion	Automatically delete PThread instance on termination of thread.
priorityLevel	Initial priority of thread.
threadName	The name of the thread (for Debug/Trace)

PThread::~PThread

(

)

Destroy the thread, this simply calls the Terminate() function with all its restrictions and penalties. See that function for more information.

Note that the correct way for a thread to terminate is to return from the Main() function.

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Member Function Documentation

static PThread* PThread::Create	(	const PNotifier &	notifier,
		const PString &	threadName
	)			[inline, static]

Parameters:

notifier	Function to execute in thread.
threadName	The name of the thread (for Debug/Trace)

static PThread* PThread::Create	(	const PNotifier &	notifier,
		INT	parameter = 0,
		AutoDeleteFlag	deletion = AutoDeleteThread,
		Priority	priorityLevel = NormalPriority,
		const PString &	threadName = PString::Empty(),
		PINDEX	stackSize = 65536
	)			[static]

Create a simple thread executing the specified notifier. This creates a simple PThread class that automatically executes the function defined by the PNotifier in the context of a new thread.

Parameters:

notifier	Function to execute in thread.
parameter	Parameter value to pass to notifier.
deletion	Automatically delete PThread instance on termination of thread.
priorityLevel	Initial priority of thread.
threadName	The name of the thread (for Debug/Trace)
stackSize	Stack size on some platforms

static PThread* PThread::Current

(

)

[static]

Get the currently running thread object instance. It is possible, even likely, that the smae code may be executed in the context of differenct threads. Under some circumstances it may be necessary to know what the current codes thread is and this static function provides that information.

Returns:

pointer to current thread.

Reimplemented in PProcess, PServiceProcess, and PHTTPServiceProcess.

static PThreadIdentifier PThread::GetCurrentThreadId

(

)

[static]

virtual Priority PThread::GetPriority

(

)

const [virtual]

Get the current priority of the thread in the current process.

Returns:

current thread priority.

virtual PThreadIdentifier PThread::GetThreadId

(

)

const [virtual]

Get operating system specific thread identifier for this thread. Note that the return value from these functions is only valid if called by the owning thread. Calling this function for another thread that may be terminating is a very bad idea.

virtual PString PThread::GetThreadName

(

)

const [virtual]

Get the name of the thread. Thread names are a optional debugging aid.

Returns:

current thread name.

Reimplemented in PProcess.

bool PThread::IsAutoDelete

(

)

const [inline]

virtual PBoolean PThread::IsSuspended

(

)

const [virtual]

Determine if the thread is currently suspended. This checks the suspension count and if greater than zero returns PTrue for a suspended thread.

Returns:

PTrue if thread is suspended.

virtual PBoolean PThread::IsTerminated

(

)

const [virtual]

Determine if the thread has been terminated or ran to completion.

Returns:

PTrue if the thread has been terminated.

virtual void PThread::Main

(

)

[pure virtual]

User override function for the main execution routine of the thread. A descendent class must provide the code that will be executed in the thread within this function.

Note that the correct way for a thread to terminate is to return from this function.

Implemented in PLibraryProcess, PThreadMain, PThread1Arg< Arg1Type >, PThread2Arg< Arg1Type, Arg2Type >, PThread3Arg< Arg1Type, Arg2Type, Arg3Type >, PThreadObj< ObjType >, PThreadObj1Arg< ObjType, Arg1Type >, PThreadObj2Arg< ObjType, Arg1Type, Arg2Type >, and PHTTPServiceThread.

void PThread::PrintOn

(

ostream &

strm

)

const [virtual]

Standard stream print function. The PObject class has a << operator defined that calls this function polymorphically.

Parameters:

strm	Stream to output text representation

Reimplemented from PObject.

void PThread::PXAbortBlock

(

)

const

int PThread::PXBlockOnChildTerminate	(	int	pid,
		const PTimeInterval &	timeout
	)

int PThread::PXBlockOnIO	(	int	handle,
		int	type,
		const PTimeInterval &	timeout
	)

virtual void PThread::Restart

(

)

[virtual]

Restart a terminated thread using the same stack priority etc that was current when the thread terminated.

If the thread is still running then this function is ignored.

virtual void PThread::Resume

(

)

[virtual]

Resume thread execution, this is identical to Suspend(PFalse).

The Resume() method may be called from within the constructor of a PThread descendant. However, the Resume() should be in the constructor of the most descendant class. So, if you have a class B (which is descended of PThread), and a class C (which is descended of B), placing the call to Resume() in the constructor of B is unwise.

If you do place a call to Resume() in the constructor, it should be at the end of the constructor, after all the other initialisation in the constructor.

The reason the call to Resume() should be at the end of the construction process is simple - you want the thread to start when all the variables in the class have been correctly initialised.

virtual void PThread::SetAutoDelete

(

AutoDeleteFlag

deletion = AutoDeleteThread

)

[virtual]

Set the flag indicating thread object is to be automatically deleted when the thread ends.

Parameters:

deletion

New auto delete setting.

void PThread::SetNoAutoDelete

(

)

[inline]

Reet the flag indicating thread object is to be automatically deleted when the thread ends.

virtual void PThread::SetPriority

(

Priority

priorityLevel

)

[virtual]

Set the priority of the thread relative to other threads in the current process.

Parameters:

priorityLevel

New priority for thread.

virtual void PThread::SetThreadName

(

const PString &

name

)

[virtual]

Change the name of the thread. Thread names are a optional debugging aid.

Returns:

current thread name.

Parameters:

name	New name for the thread.

Reimplemented in PProcess.

static void PThread::Sleep

(

const PTimeInterval &

delay

)

[static]

Suspend the current thread for the specified amount of time.

Parameters:

delay

Time interval to sleep for.

virtual void PThread::Suspend

(

PBoolean

susp = PTrue

)

[virtual]

Suspend or resume the thread.

If susp is PTrue this increments an internal count of suspensions that must be matched by an equal number of calls to Resume()# or Suspend(PFalse) before the thread actually executes again.

If susp is PFalse then this decrements the internal count of suspensions. If the count is <= 0 then the thread will run. Note that the thread will not be suspended until an equal number of Suspend(PTrue) calls are made.

Parameters:

susp	Flag to suspend or resume a thread.

virtual void PThread::Terminate

(

)

[virtual]

Terminate the thread. It is highly recommended that this is not used except in abnormal abort situations as not all clean up of resources allocated to the thread will be executed. This is especially true in C++ as the destructors of objects that are automatic variables are not called causing at the very least the possiblity of memory leaks.

Note that the correct way for a thread to terminate is to return from the Main() function or self terminate by calling Terminate() within the context of the thread which can then assure that all resources are cleaned up.

Reimplemented in PProcess, and PServiceProcess.

PBoolean PThread::WaitForTermination

(

const PTimeInterval &

maxWait

)

const

Block and wait for the thread to terminate.

Returns:

PFalse if the thread has not terminated and the timeout has expired, PTrue otherwise.

Parameters:

maxWait

Maximum time to wait for termination.

void PThread::WaitForTermination

(

)

const

Block and wait for the thread to terminate.

static void PThread::Yield

(

)

[static]

Yield to another thread without blocking. This duplicates the implicit thread yield that may occur on some I/O operations or system calls.

This may not be implemented on all platforms.

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Friends And Related Function Documentation

friend class PExternalThread [friend]

friend class PHouseKeepingThread [friend]

Reimplemented in PProcess.

friend class PProcess [friend]

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

• thread.h

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