overwrite_buffer Class

An overwrite_buffer messaging block is a multi-target, multi-source, ordered propagator_block capable of storing a single message at a time. New messages overwrite previously held ones.

Syntax

template<class T>
class overwrite_buffer : public propagator_block<multi_link_registry<ITarget<T>>, multi_link_registry<ISource<T>>>;

Parameters

T
The payload type of the messages stored and propagated by the buffer.

Members

Public Constructors

Public Methods

Protected Methods

Remarks

An overwrite_buffer messaging block propagates out copies of its stored message to each of its targets.

For more information, see Asynchronous Message Blocks.

Inheritance Hierarchy

ISource

ITarget

source_block

propagator_block

overwrite_buffer

Requirements

Header: agents.h

Namespace: concurrency

accept_message

Accepts a message that was offered by this overwrite_buffer messaging block, returning a copy of the message to the caller.

virtual message<T>* accept_message(runtime_object_identity _MsgId);

Parameters

_MsgId
The runtime_object_identity of the offered message object.

Return Value

A pointer to the message object that the caller now has ownership of.

Remarks

The overwrite_buffer messaging block returns copies of the message to its targets, rather than transferring ownership of the currently held message.

consume_message

Consumes a message previously offered by the overwrite_buffer messaging block and reserved by the target, returning a copy of the message to the caller.

virtual message<T>* consume_message(runtime_object_identity _MsgId);

Parameters

_MsgId
The runtime_object_identity of the message object being consumed.

Return Value

A pointer to the message object that the caller now has ownership of.

Remarks

Similar to accept, but is always preceded by a call to reserve.

has_value

Checks whether this overwrite_buffer messaging block has a value yet.

bool has_value() const;

Return Value

true if the block has received a value, false otherwise.

link_target_notification

A callback that notifies that a new target has been linked to this overwrite_buffer messaging block.

virtual void link_target_notification(_Inout_ ITarget<T>* _PTarget);

Parameters

_PTarget
A pointer to the newly linked target.

~overwrite_buffer

Destroys the overwrite_buffer messaging block.

~overwrite_buffer();

overwrite_buffer

Constructs an overwrite_buffer messaging block.

overwrite_buffer();

overwrite_buffer(
    filter_method const& _Filter);

overwrite_buffer(
    Scheduler& _PScheduler);

overwrite_buffer(
    Scheduler& _PScheduler,
    filter_method const& _Filter);

overwrite_buffer(
    ScheduleGroup& _PScheduleGroup);

overwrite_buffer(
    ScheduleGroup& _PScheduleGroup,
    filter_method const& _Filter);

Parameters

_Filter
A filter function which determines whether offered messages should be accepted.

_PScheduler
The Scheduler object within which the propagation task for the overwrite_buffer messaging block is scheduled.

_PScheduleGroup
The ScheduleGroup object within which the propagation task for the overwrite_buffer messaging block is scheduled. The Scheduler object used is implied by the schedule group.

Remarks

The runtime uses the default scheduler if you do not specify the _PScheduler or _PScheduleGroup parameters.

The type filter_method is a functor with signature bool (T const &) which is invoked by this overwrite_buffer messaging block to determine whether or not it should accept an offered message.

propagate_message

Asynchronously passes a message from an ISource block to this overwrite_buffer messaging block. It is invoked by the propagate method, when called by a source block.

virtual message_status propagate_message(
    _Inout_ message<T>* _PMessage,
    _Inout_ ISource<T>* _PSource);

Parameters

_PMessage
A pointer to the message object.

_PSource
A pointer to the source block offering the message.

Return Value

A message_status indication of what the target decided to do with the message.

propagate_to_any_targets

Places the message _PMessage in this overwrite_buffer messaging block and offers it to all of the linked targets.

virtual void propagate_to_any_targets(_Inout_ message<T>* _PMessage);

Parameters

_PMessage
A pointer to a message object that this overwrite_buffer has taken ownership of.

Remarks

This method overwrites the current message in the overwrite_buffer with the newly accepted message _PMessage.

send_message

Synchronously passes a message from an ISource block to this overwrite_buffer messaging block. It is invoked by the send method, when called by a source block.

virtual message_status send_message(
    _Inout_ message<T>* _PMessage,
    _Inout_ ISource<T>* _PSource);

Parameters

_PMessage
A pointer to the message object.

_PSource
A pointer to the source block offering the message.

Return Value

A message_status indication of what the target decided to do with the message.

supports_anonymous_source

Overrides the supports_anonymous_source method to indicate that this block can accept messages offered to it by a source that is not linked.

virtual bool supports_anonymous_source();

Return Value

true because the block does not postpone offered messages.

release_message

Releases a previous message reservation.

virtual void release_message(runtime_object_identity _MsgId);

Parameters

_MsgId
The runtime_object_identity of the message object being released.

reserve_message

Reserves a message previously offered by this overwrite_buffer messaging block.

virtual bool reserve_message(runtime_object_identity _MsgId);

Parameters

_MsgId
The runtime_object_identity of the message object being reserved.

Return Value

true if the message was successfully reserved, false otherwise.

Remarks

After reserve is called, if it returns true, either consume or release must be called to either take or release ownership of the message.

resume_propagation

Resumes propagation after a reservation has been released.

virtual void resume_propagation();

value

Gets a reference to the current payload of the message being stored in the overwrite_buffer messaging block.

T value();

Return Value

The payload of the currently stored message.

Remarks

The value stored in the overwrite_buffer could change immediately after this method returns. This method will wait until a message arrives if no message is currently stored in the overwrite_buffer.

See also

concurrency Namespace
unbounded_buffer Class
single_assignment Class