RWTThreadIOUFunction< Return > Class Template Reference
[Threading]

Handle class for functor-based threaded runnable objects. More...

#include <rw/thread/RWTThreadIOUFunction.h>

Inheritance diagram for RWTThreadIOUFunction< Return >:

List of all members.

Public Member Functions
	RWTThreadIOUFunction ()
	RWTThreadIOUFunction (const RWTThreadIOUFunction< Return > &second)
	~RWTThreadIOUFunction ()
RWTThreadIOUFunction< Return > &	operator= (const RWTThreadIOUFunction< Return > &second)
RWTIOUResult< Return >	operator() () const
RWTFunctorR0< Return >	getFunctor () const
RWTIOUResult< Return >	result () const
void	setFunctor (const RWTFunctorR0< Return > &functor)
void	setIOUEscrow (const RWTIOUEscrow< Return > &escrow)
Static Public Member Functions
static RWTThreadIOUFunction < Return >	make ()
static RWTThreadIOUFunction < Return >	make (const RWTFunctorR0< Return > &functor)
static RWTThreadIOUFunction < Return >	make (const RWTIOUEscrow< Return > &escrow, const RWTFunctorR0< Return > &functor)
static RWTThreadIOUFunction < Return >	make (const RWTFunctorR0< Return > &functor, const RWThreadAttribute &attr)
static RWTThreadIOUFunction < Return >	make (const RWTIOUEscrow< Return > &escrow, const RWTFunctorR0< Return > &functor, const RWThreadAttribute &attr)

---

Detailed Description

template<class Return>
class RWTThreadIOUFunction< Return >

The RWTThreadIOUFunction class is a handle class for functor-based threaded runnable objects.

A runnable object provides the basic mechanisms used to create, control, and monitor the threads of execution within your application. Runnables are used to define the task or activity to be performed by a thread.

Each runnable object is reference-counted. A threaded runnable body instance keeps a count of the number of handles that currently reference it. A runnable object is deleted when the last handle that references the body is deleted.

A functor-based runnable accepts a functor object for execution. A functor is an object used to encapsulate a function call. Each functor keeps a pointer to the function and copies of the argument values that are to be passed to the function. Invoking a functor produces a call to the function, and in this case, a return value.

A functor-based runnable simply redefines the basic run() member to invoke a functor instance stored within the runnable. With this capability, you do not have to resort to sub-classing or other intrusive techniques to customize the execution behavior of a runnable. The functor-based runnables allow you to dynamically specify the functions you want to execute when a runnable is started.

RWTThreadIOUFunction is used to access a threaded runnable, which creates a new thread to execute the specified functor. The result of the functor is returned in the form of an IOU. An IOU may be obtained as soon as the runnable is created. To get the actual result from the IOU you must redeem it. If the result has not yet been calculated, the calling thread blocks until it has.

Although functors are central to the inner workings of Threading package classes, you may not need to deal with functors directly. Instead, the rwtMakeThreadIOUFunction() global template functions and macros can build the appropriate functor instance and use it to initialize an RWTThreadIOUFunction object directly from a function pointer.

Examples

 #include <iostream.h>
 #include <math.h>
 #include <rw/thread/RWTThreadIOUFunction.h>
 #include <rw/itc/RWTIOUResult.h>
 #include <rw/thread/rwtMakeThreadIOUFunction.h>
 
 int greatestPrime(int limit)
 {
    // The sieve of Eratosthenes:
    int i, m;
    char* sieve = new char[limit + 1];
    if (sieve == 0) return -1;  // not enough memory
 
    for (i=0; i<=limit; ++i) sieve[i] = 1;
    for (i=2; i<=sqrt(limit); ++i)
      if (sieve[i] != 0)
        for (m=i+i; m<=limit; m+=i) sieve[m] = 0;
 
    // Return the greatest prime less than or equal to limit:
    for (i=limit; i>=2; --i)
      if (sieve[i] != 0) return i;
 }
 
 int main()
 {
   RWTThreadIOUFunction<int> lastprime
     = rwtMakeThreadIOUFunction(greatestPrime, 6000000);
 
   lastprime.start();  // spawn thread to calculate big prime
   RWTIOUResult<int> answer = lastprime.result();  // get an IOU
 
   // While the thread is busy calculating, print this
   // suspenseful message to keep the user entertained:
   cout << "The greatest prime less than six million is... "
        << flush;
 
   // Block until the answer has been calculated and
   // then print it:
   cout << answer.redeem() << endl;
   return 0;
 }

Program output:

 The greatest prime less than six million is... 5999993

See also:

RWTFunctorR0, RWThread, RWRunnable, RWRunnableHandle, RWThreadAttribute, rwtMakeThreadIOUFunction()

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Constructor & Destructor Documentation

template<class Return >

RWTThreadIOUFunction< Return >::RWTThreadIOUFunction

(

)

[inline]

Constructs an empty RWTThreadIOUFunction handle instance.

template<class Return >

RWTThreadIOUFunction< Return >::RWTThreadIOUFunction

(

const RWTThreadIOUFunction< Return > &

second

)

[inline]

Binds a new handle to the runnable instance, if any, pointed to by the handle second.

template<class Return >

RWTThreadIOUFunction< Return >::~RWTThreadIOUFunction

(

)

[inline]

Destructor.

---

Member Function Documentation

template<class Return>

RWTFunctorR0<Return> RWTThreadIOUFunction< Return >::getFunctor

(

)

const

Gets the current functor instance, if any, associated with the runnable. Possible exceptions include RWTHRInvalidPointer and RWTHRInternalError.

template<class Return>

static RWTThreadIOUFunction<Return> RWTThreadIOUFunction< Return >::make	(	const RWTIOUEscrow< Return > &	escrow,
		const RWTFunctorR0< Return > &	functor,
		const RWThreadAttribute &	attr
	)			[static]

Constructs and returns an RWTThreadIOUFunction that executes the specified functor when started. A new thread is created using the attributes given by attr, and the functor result is stored in escrow.

template<class Return>

static RWTThreadIOUFunction<Return> RWTThreadIOUFunction< Return >::make	(	const RWTFunctorR0< Return > &	functor,
		const RWThreadAttribute &	attr
	)			[static]

Constructs and returns an RWTThreadIOUFunction that executes the specified functor when started. A new thread is created using the attributes given by attr.

template<class Return>

static RWTThreadIOUFunction<Return> RWTThreadIOUFunction< Return >::make	(	const RWTIOUEscrow< Return > &	escrow,
		const RWTFunctorR0< Return > &	functor
	)			[static]

Constructs and returns an RWTThreadIOUFunction that executes the specified functor when started, and places the functor result in escrow.

template<class Return>

static RWTThreadIOUFunction<Return> RWTThreadIOUFunction< Return >::make

(

const RWTFunctorR0< Return > &

functor

)

[static]

Constructs and returns an RWTThreadIOUFunction that executes the specified functor when started.

template<class Return>

static RWTThreadIOUFunction<Return> RWTThreadIOUFunction< Return >::make

(

)

[static]

Constructs and returns an RWTThreadIOUFunction object with an undefined functor. The setFunctor() member must be used to define a functor prior to starting.

template<class Return>

RWTIOUResult<Return> RWTThreadIOUFunction< Return >::operator()

(

)

const

Returns the IOU that will receive the result of the function.

template<class Return >

RWTThreadIOUFunction< Return > & RWTThreadIOUFunction< Return >::operator=

(

const RWTThreadIOUFunction< Return > &

second

)

[inline]

Binds this to the runnable instance, if any, pointed to by the handle second.

template<class Return>

RWTIOUResult<Return> RWTThreadIOUFunction< Return >::result

(

)

const

Returns the IOU that will receive the result of the function.

template<class Return>

void RWTThreadIOUFunction< Return >::setFunctor

(

const RWTFunctorR0< Return > &

functor

)

Sets the functor to be executed by this runnable. Possible exceptions include RWTHRInvalidPointer and RWTHRInternalError.

template<class Return>

void RWTThreadIOUFunction< Return >::setIOUEscrow

(

const RWTIOUEscrow< Return > &

escrow

)

Specifies an IOU escrow that is to receive the result of the function. The new IOU is not used until the next time start() is called. Each time an RWTThreadIOUFunction object is restarted, it checks its current IOU escrow handle to see if it is valid, and if so, checks to see whether the escrow has already been used to capture a result or exception, or has been aborted. If the escrow object is found to be in any of these "redeemable" states, a new escrow instance is automatically created to capture the next result. Possible exceptions include RWTHRInvalidPointer and RWTHRInternalError.