RWTIOUEscrow< Redeemable > Class Template Reference
[Interthread Communication]

A writable IOU handle. More...

#include <rw/itc/RWTIOUEscrow.h>

Inheritance diagram for RWTIOUEscrow< Redeemable >:

List of all members.

Public Types
typedef Redeemable	RedeemableType
Public Member Functions
	~RWTIOUEscrow (void)
	RWTIOUEscrow (void)
	RWTIOUEscrow (const RWTEscrowHandle< Redeemable > &escrowHandle)
	RWTIOUEscrow (const RWTIOUEscrow< Redeemable > &second)
RWTIOUEscrow< Redeemable > &	operator= (const RWTIOUEscrow< Redeemable > &second)
bool	aborted (void) const
void	close (const Redeemable &value)
bool	closeable (void) const
bool	closed (void)
bool	inError (void)
RWTIOUEscrow< Redeemable >	newInstance (void) const
void	operator() (const Redeemable &value)
void	operator= (const Redeemable &value)
bool	redeemed (void) const
void	setException (const RWTHRxmsg &xmsg)
void	setException (const RWCString &msg)
Protected Member Functions
RWTEscrowImp< Redeemable > &	body (void) const

---

Detailed Description

template<class Redeemable>
class RWTIOUEscrow< Redeemable >

An RWTIOUEscrow<Redeemable> is a writable IOU handle. An IOU, also known as a future, is a promise for a value that is forthcoming -- a placeholder for that value. Usually the writer of an IOU and the reader (or readers) of an IOU are in different threads of control. In this sense IOUs are a mechanism for interthread communication.

An IOU is a write once/read many structure. It may only be written to once, but may be read any number of times.

The template parameter Redeemable is the value type of IOU result. This type must provide a public copy constructor, and must allow dynamic allocation using operator new.

The RWTIOUEscrow<Redeemable> is the handle through which a value is eventually written to an underlying escrow object. One or more readers may redeem that value once it is available by using any RWTIOUResult<Redeemable> handle that is bound to the same escrow instance.

An RWTIOUEscrow<Redeemable> is a reference counted handle to an RWTEscrowImp<Redeemable> . It can be copied and passed by value. When the last handle to a given RWTEscrowImp<Redeemable> is destroyed, the internal RWTEscrowImp<Redeemable> is destroyed.

An RWTIOUEscrow<Redeemable> can be initialized by or assigned to an RWTIOUResult<Redeemable> , and vice versa. Both are interfaces to the same underlying RWTIOUEscrowImp<Redeemable>. RWTIOUEscrow<Redeemable> is a write interface, and RWTIOUResult<Redeemable> is a read interface.

An exception may be set on an IOU by the holder of an RWTIOUEscrow<Redeemable> . This will cause the exception to be thrown when an attempt is made to redeem it.

Similarly, an IOU may be aborted by the holder of an RWTIOUResult<Redeemable> . This will cause an exception to be thrown if an attempt is made to redeem the IOU or to set its value.

An RWTIOUEscrow<Redeemable> is closable if a value has not been set, it has not been aborted, and no exception has been set.

Examples

 #include <rw/itc/RWTIOUEscrow.h>             // for RWTIOUEscrow
 #include <rw/itc/RWTIOUResult.h>             // for RWTIOUResult
 #include <rw/thread/RWRunnableSelf.h>        // for ::rwSleep()
 #include <rw/thread/RWThreadFunction.h>      // for RWThreadFunction
 #include <rw/thread/rwtMakeThreadFunction.h  // for
                                              // rwtMakeThreadFunction
 #include <rw/thread/rwtMakeThreadIOU.h>      // for rwtMakeThreadIOU
 #include <rw/itc/rwtMakeIOUCallback.h>       // for rwtMakeIOUCallback
 
 
 // This function is started in a thread and is passed an
 // RWTIOUEscrow<int>.
 // It is expected to close the escrow.
 void sixteen(RWTIOUEscrow<int> iouInt)
 {
    ::rwSleep(500); // simulate useful activity
    iouInt = 16;    // close escrow
 }
 
 void callback(RWTIOUResult<int> intIOUResult) {
    try {
       int val = intIOUResult;  // redeem value
       cout << "callback received value of " << val << endl;
    }
    catch (...) { cout << "something bad happened" << endl; }
 }
 
 int main()
 {
    try {
       RWThreadFunction thread;
 
       // Create an RWTIOUResult<int> using the
       // rwtMakeThreadIOU() helper function. This specifies
       // that the IOU should be thread safe and the
       // Redeemable type is int.
       RWTIOUResult<int> intResult = rwtMakeThreadIOU((int*)0);
 
       // create thread, pass in RWTIOUResult<int> as additional
       // arg. intResult will be converted into an
       // RWTIOUEscrow<int> in sixteen()
       thread = rwtMakeThreadFunction(sixteen, intResult);
 
       // register callback
       intResult.addCallback(rwtMakeIOUCallback(callback));
 
       thread.start();
 
       // block, wait for result
       int val = intResult;
       cout << "redeemed " << val << endl;
    }
    catch (...) {
       cout << "something bad happened" << endl;
    }
    return 0;
 }

---

Member Typedef Documentation

template<class Redeemable>

typedef Redeemable RWTIOUEscrow< Redeemable >::RedeemableType

A synonym for the value type of the IOU, or future, result.

Reimplemented from RWTEscrowHandle< Redeemable >.

---

Constructor & Destructor Documentation

template<class Redeemable >

RWTIOUEscrow< Redeemable >::~RWTIOUEscrow

(

void

)

[inline]

Destroys the handle and decrements the reference count of the current escrow instance, if any, deleting the escrow if its reference count reaches zero.

template<class Redeemable >

RWTIOUEscrow< Redeemable >::RWTIOUEscrow

(

void

)

[inline]

Creates an empty, invalid handle. Use of an instance created by the default constructor results in an RWTHRInvalidPointer exception being thrown. You can determine if an RWTIOUEscrow<Redeemable> handle is valid by calling the isValid() member function, which is inherited from the RWHandleBase base class.

template<class Redeemable>

RWTIOUEscrow< Redeemable >::RWTIOUEscrow

(

const RWTEscrowHandle< Redeemable > &

escrowHandle

)

[inline]

Constructs a new handle instance and attaches it to the escrow instance, if any, pointed to by escrowHandle, and increments the escrow's reference count. This constructor allows an RWTIOUEscrow<Redeemable> to be constructed from an RWTIOUResult<Redeemable> .

template<class Redeemable>

RWTIOUEscrow< Redeemable >::RWTIOUEscrow

(

const RWTIOUEscrow< Redeemable > &

second

)

[inline]

Copy constructor. Constructs a new handle instance and attaches it to the escrow instance, if any, pointed to by second, and increments the escrow's reference count.

---

Member Function Documentation

template<class Redeemable >

bool RWTIOUEscrow< Redeemable >::aborted

(

void

)

const [inline]

Returns true if the IOU has been aborted, otherwise returns false. Possible exceptions include RWTHRInvalidPointer.

template<class Redeemable >

RWTEscrowImp< Redeemable > & RWTIOUEscrow< Redeemable >::body

(

void

)

const [inline, protected]

Gets a reference for the body instance, if any.

Exceptions:

RWTHRInvalidPointer

Thrown if this handle is not attached to a body.

Reimplemented from RWHandleBase.

template<class Redeemable>

void RWTIOUEscrow< Redeemable >::close

(

const Redeemable &

value

)

[inline]

Stores a value into the underlying escrow. If the IOU has already been closed, the function throws an RWTHREscrowAlreadyClosed exception. If the escrow operation has been aborted, the function throws an RWTHROperationAborted exception. If an exception has been set, that exception is thrown.

template<class Redeemable >

bool RWTIOUEscrow< Redeemable >::closeable

(

void

)

const [inline]

Returns true if the IOU has not been closed, and is not in an error condition or aborted; otherwise returns false. Possible exceptions include RWTHRInvalidPointer.

template<class Redeemable >

bool RWTIOUEscrow< Redeemable >::closed

(

void

)

[inline]

Returns true if the IOU has been closed, otherwise returns false. Possible exceptions include RWTHRInvalidPointer.

template<class Redeemable >

bool RWTIOUEscrow< Redeemable >::inError

(

void

)

[inline]

Returns true if the IOU has been closed with an error, otherwise returns false. Possible exceptions include RWTHRInvalidPointer.

template<class Redeemable >

RWTIOUEscrow< Redeemable > RWTIOUEscrow< Redeemable >::newInstance

(

void

)

const [inline]

Creates a new instance of the same class as the current concrete RWTEscrowImp<Redeemable> body. Returns a new RWTIOUEscrow<Redeemable> handle that points to the new body.

template<class Redeemable>

void RWTIOUEscrow< Redeemable >::operator()

(

const Redeemable &

value

)

[inline]

Equivalent to close().

template<class Redeemable>

void RWTIOUEscrow< Redeemable >::operator=

(

const Redeemable &

value

)

[inline]

Equivalent to close().

template<class Redeemable>

RWTIOUEscrow< Redeemable > & RWTIOUEscrow< Redeemable >::operator=

(

const RWTIOUEscrow< Redeemable > &

second

)

[inline]

Detaches this handle from its current escrow instance, if any, decrementing the escrow's reference count and deleting the escrow if the count reaches zero. It then attaches to the escrow instance, if any, pointed to by second, and increments the new escrow's reference count.

template<class Redeemable >

bool RWTIOUEscrow< Redeemable >::redeemed

(

void

)

const [inline]

Returns true if the IOU has been successfully redeemed at least once, otherwise returns false. Possible exceptions include RWTHRInvalidPointer.

template<class Redeemable >

void RWTIOUEscrow< Redeemable >::setException

(

const RWCString &

msg

)

[inline]

Used to indicate that IOU result could not be produced because an exception occurred. The string message is packaged in an RWTHRxmsg and stored inside the IOU escrow object. The stored exception is thrown in response to any attempt to redeem the IOU. If the IOU has already either been closed normally, closed with an error, or aborted, the error is ignored.

template<class Redeemable >

void RWTIOUEscrow< Redeemable >::setException

(

const RWTHRxmsg &

xmsg

)

[inline]

Used to indicate that IOU result could not be produced because an exception occurred. Causes a copy of the specified exception to be stored inside the IOU escrow object. The stored exception is rethrown in response to any attempt to redeem the IOU. If the IOU has already either been closed normally, closed with an error, or aborted, the error is ignored.