class PThread

This class defines a thread of execution in the system.

Inheritance:


Public Methods

[more] Overrides from PObject
[more] Control functions
[more] Miscellaneous

Public Members

[more] Construction


Inherited from PObject:

Public Methods

Run Time Type functions

I/O functions

Public Members

Comparison functions


Documentation

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 PWLib has some support for co-operative threads, but this has been removed

o Construction

oenum Priority
Codes for thread priorities

o LowestPriority
Will only run if all other threads are blocked

o LowPriority
Runs approximately half as often as normal

o NormalPriority
Normal priority for a thread

o HighPriority
Runs approximately twice as often as normal

o HighestPriority
Is only thread that will run, unless blocked

oenum AutoDeleteFlag
Codes for thread autodelete flag

o AutoDeleteThread
Automatically delete thread object on termination

o NoAutoDeleteThread
Don't delete thread as it may not be on heap

o PThread( PINDEX, AutoDeleteFlag deletion = AutoDeleteThread, Priority priorityLevel = NormalPriority, const PString & threadName = PString::Empty() )
Create a new thread instance. Unless the startSuspended parameter is TRUE, 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:
PINDEX - Not used - previously stack size
deletion - Automatically delete PThread instance on termination of thread.
priorityLevel - Initial priority of thread.
threadName - The name of the thread (for Debug/Trace)

o ~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.

o Overrides from PObject

ovoid PrintOn( ostream & strm ) const
Standard stream print function. The PObject class has a << operator defined that calls this function polymorphically.
Parameters:
- strm Stream to output text representation

o Control functions

ovirtual void Restart()
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.

ovirtual void Terminate()
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.

ovirtual BOOL IsTerminated() const
Determine if the thread has been terminated or ran to completion.

Returns:
TRUE if the thread has been terminated.

ovoid WaitForTermination() const
Block and wait for the thread to terminate.

Returns:
FALSE if the thread has not terminated and the timeout has expired.

ovirtual void Suspend( BOOL susp = TRUE )
Suspend or resume the thread.

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

If susp is FALSE 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(TRUE) calls are made.

Parameters:
susp - Flag to suspend or resume a thread.

ovirtual void Resume()
Resume thread execution, this is identical to Suspend(FALSE)

ovirtual BOOL IsSuspended() const
Determine if the thread is currently suspended. This checks the suspension count and if greater than zero returns TRUE for a suspended thread.

Returns:
TRUE if thread is suspended.

ostatic void Sleep( const PTimeInterval & delay )
Suspend the current thread for the specified amount of time.
Parameters:
- delay Time interval to sleep for.

ovirtual void SetPriority( Priority priorityLevel )
Set the priority of the thread relative to other threads in the current process.
Parameters:
priorityLevel - New priority for thread.

ovirtual Priority GetPriority() const
Get the current priority of the thread in the current process.

Returns:
current thread priority.

ovirtual void SetAutoDelete( AutoDeleteFlag deletion = AutoDeleteThread )
Set the flag indicating thread object is to be automatically deleted when the thread ends.
Parameters:
deletion - New auto delete setting.

ovoid SetNoAutoDelete()
Reet the flag indicating thread object is to be automatically deleted when the thread ends

ovirtual PString GetThreadName() const
Get the name of the thread. Thread names are a optional debugging aid.

Returns:
current thread name.

ovirtual void SetThreadName( const PString & name )
Change the name of the thread. Thread names are a optional debugging aid.

Parameters:
name - New name for the thread.
Returns:
current thread name.

o Miscellaneous

ovirtual PThreadIdentifier GetThreadId() const
Get operating system specific thread identifier for this thread

ostatic PThreadIdentifier GetCurrentThreadId()
Get operating system specific thread identifier for current thread

ovirtual void Main() = 0
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.

ostatic PThread* Current()
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.

ostatic void Yield()
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.

ostatic PThread* Create( const PNotifier & notifier, INT parameter = 0, AutoDeleteFlag deletion = AutoDeleteThread, Priority priorityLevel = NormalPriority, const PString & threadName = PString::Empty(), PINDEX stackSize = 10000 )
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


Direct child classes:
PProcess
Friends:
class PProcess
class PTrace::Block

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