Tasking Event-B Overview - Revision history

imported>Andy: /* Implementing Events */

2013-09-02T08:43:33Z

Implementing Events

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	*** A local-only event - the event only contains local updates, which are expanded to update actions in the implementation. In this case guards not permitted in the event.		*** A local-only event - the event only contains local updates, which are expanded to update actions in the implementation. In this case guards not permitted in the event.
	*** A synchronizing event - local updates are expanded to become update actions in the implementation, remote updates are performed by subroutine call. Guards in the remote event may block; in Ada this is implemented as an entry barrier, and in C can be implemented using a pthread condition variable.		*** A synchronizing event - local updates are expanded to become update actions in the implementation, remote updates are performed by subroutine call. Guards in the remote event may block; in Ada this is implemented as an entry barrier, and in C can be implemented using a pthread condition variable.
	** Sensing annotation - This annotation is added to an event in the EMF tree. It identifies an event as one that maps to a read, from the environment. If the environment is simulated, i.e. without address variables, then the sensing event has an update action that models assignment of a return value from a subroutine call. If the event has addressed variables associated with its event parameters, then they map to direct reads from memory mapped variables in the generated code.
	** Actuating - This annotation is added to an event in the EMF tree. It identifies an event as one that maps to a write, to some variable in the environment. If the environment is simulated, without address variables, then the actuating event has no update action. If a sensing event has addressed variables associated with its parameters then they map to direct writes, to memory mapped variables in the generated code.

	Sensing (and actuating) events make use of synchronization. The sensing/actuating synchronizations only occur between AutoTasks and Environ machines. The data exchange, in sensing and actuating events, is modelled by the event parameters, and the result from the decomposition step. Shared machine events are mapped to subroutine declarations, and their parameters are always implemented as formal parameters. Formal parameters are place-holders in a subroutine; they are replaced by the actual parameters at run-time. To assist the code generator, we automatically identify the parameter direction during translation. We identify them as either ''in'' or ''out'' parameters.

	~~===== Addressed Variables =====~~
	When sensing monitored variables, or actuating controlled variables, in the environment we can use explicit memory addresses. We can link a task's event parameters, and an Environ machines machine variables with specific addresses, we then implement these in such a way that we can read/write from these in the generated code. <span style="color: RED">Addressed variables are on the TODO list</span>, see [[ Outstanding Tooling Issues]]

	=== Theories, for Generating Code ===		=== Theories, for Generating Code ===

imported>Andy: /* Synchronization */

2013-09-02T08:31:05Z

Synchronization

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	Synchronization between local events (in AutoTasks) and remote events (in shared/Environ Machines) is determined using the composed machine. To use an event simply enter its name in the TaskBody editor. The translator will in-line any local actions, and add a call to perform remote updates, and obtain remote data.		Synchronization between local events (in AutoTasks) and remote events (in shared/Environ Machines) is determined using the composed machine. To use an event simply enter its name in the TaskBody editor. The translator will in-line any local actions, and add a call to perform remote updates, and obtain remote data.

	Synchronization corresponds to:		Synchronization can corresponds to:
	* a subroutine call from task to ~~shared machine~~, or,		* a subroutine call from a task to protected object, or,
	* ~~sensing or actuating~~ of ~~environment variables~~.		* a subroutine call from task to environment simulation (only for events used with a state-machine, when using the read/evaluate/write style of translation).
			* a rendezvous between a task and environ simulation (for events specified in a task body (i.e. at an time other than state-machine style above)).

	In the case of a subroutine call the subroutine is an atomic (with respect to an external viewer) update to state. The updates in the protected resource are implemented by a procedure call to a protected object, and tasks do not share state~~. The synchronization construct also provides the means to specify parameter passing, both in and out of the task.~~		In the case of a subroutine call the subroutine is an atomic (with respect to an external viewer) update to state. The updates in the protected resource are implemented by a procedure call to a protected object, and tasks do not share state.

	~~In the case of a sensing or actuating event, the updates of the action correspond to reads of monitored variables, and writes to controlled variables of the environment~~.

	=== Implementing Events ===		=== Implementing Events ===

imported>Andy: /* Event Translation */

2013-09-02T08:15:23Z

Event Translation

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	When an event, used in the task body, is translated to an implementation its translation depends on where it is used in the task body. The mappings are relatively simple for branch, loop, and sequence; but, in addition to the parent construct, the Event translation depends on whether it is part of a synchronization. Obviously the simplest translation is when no synchronization is involved. The translator checks the composed machine to see if the event is paired in a combined event. We say that events is a Tasking machine are local, and that events in a Shared or Environ machine, are remote. If there is no synchronization, then the actions of the local event are expanded in-line in the subroutine body.		When an event, used in the task body, is translated to an implementation its translation depends on where it is used in the task body. The mappings are relatively simple for branch, loop, and sequence; but, in addition to the parent construct, the Event translation depends on whether it is part of a synchronization. Obviously the simplest translation is when no synchronization is involved. The translator checks the composed machine to see if the event is paired in a combined event. We say that events is a Tasking machine are local, and that events in a Shared or Environ machine, are remote. If there is no synchronization, then the actions of the local event are expanded in-line in the subroutine body.

	<span style="color: RED">'''~~Caution~~''': As a result of the decomposition process, the tool can produce a remote event, without a corresponding local event. A local event, with no guards and skip action, must be added manually to the tasking machine, and composed machine ~~in order to facilitate~~ code ~~generation. This relates to~~ an implementation with a subroutine call~~, where there are~~ no parameters ~~passed, and no local updates i.e.~~ remote updates ~~only~~. The addition of the 'dummy' event will be automated ~~in a pre-processing step~~ in the ~~near~~ future. It is not necessary to have a dummy remote event if a remote event does not exist.</span>		<span style="color: RED">'''Note''': As a result of the decomposition process, the decomposition tool can produce a remote event, without a corresponding local event. This happens when modelling a task that updates a (remote) shared machine, but does not pass any parameters and has no local update. A local event, with no guards and skip action, must be added manually to the tasking machine, and also added to the composed machine. The code generator will then create an implementation with a subroutine call (with no parameters) causing only remote updates. The addition of the 'dummy' event will be automated in the future. It is not necessary to have a dummy remote event if a remote event does not exist.</span>

	See [[ Outstanding Tooling Issues]]		See [[ Outstanding Tooling Issues]]

imported>Andy: /* Control Constructs (used in the Task body) */

2013-08-29T14:57:46Z

Control Constructs (used in the Task body)

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	=== Control of Program Flow ===		=== Control of Program Flow ===
	At the implementation stage we need to think about controlling the flow of execution; and where interaction with the environment is concerned, how events should be implemented. The following section describes the constructs that we have introduced to facilitate this.		At the implementation stage we need to think about controlling the flow of execution; and where interaction with the environment is concerned, how events should be implemented. The following section describes the constructs that we have introduced to facilitate this.
	==== Control Constructs (used in the Task body) ====		==== Control Constructs used in the Task body ====
	Each Tasking Machine has a ''task body'' which contains the flow control (algorithmic constructs).		Each Tasking Machine has a ''task body'' which contains the flow control (algorithmic constructs).

imported>Andy: /* Tasking Event-B */

2013-08-29T14:57:32Z

Tasking Event-B

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	\|[http://wiki.event-b.org/index.php/Tasking_Event-B_Overview#Tasking_Machines AutoTask], [http://wiki.event-b.org/index.php/Tasking_Event-B_Overview#Shared_Machines Shared], [http://wiki.event-b.org/index.php/Tasking_Event-B_Overview#The_Environ_Machine Environ]		\|[http://wiki.event-b.org/index.php/Tasking_Event-B_Overview#Tasking_Machines AutoTask], [http://wiki.event-b.org/index.php/Tasking_Event-B_Overview#Shared_Machines Shared], [http://wiki.event-b.org/index.php/Tasking_Event-B_Overview#The_Environ_Machine Environ]
	\|-		\|-
	\|[http://wiki.event-b.org/index.php/Tasking_Event-B_Overview#~~Control_Constructs_(used_in_the_Task_body)~~ Task body]		\|[http://wiki.event-b.org/index.php/Tasking_Event-B_Overview#Control_Constructs_used_in_the_Task_body Task body]
	\|Sequence, Loop, Branch, Event, Output		\|Sequence, Loop, Branch, Event, Output
	\|-		\|-

imported>Andy: /* Tasking Event-B */

2013-08-29T14:56:35Z

Tasking Event-B

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	\|[http://wiki.event-b.org/index.php/Tasking_Event-B_Overview#Tasking_Machines AutoTask], [http://wiki.event-b.org/index.php/Tasking_Event-B_Overview#Shared_Machines Shared], [http://wiki.event-b.org/index.php/Tasking_Event-B_Overview#The_Environ_Machine Environ]		\|[http://wiki.event-b.org/index.php/Tasking_Event-B_Overview#Tasking_Machines AutoTask], [http://wiki.event-b.org/index.php/Tasking_Event-B_Overview#Shared_Machines Shared], [http://wiki.event-b.org/index.php/Tasking_Event-B_Overview#The_Environ_Machine Environ]
	\|-		\|-
	\|[http://wiki.event-b.org/index.php/Tasking_Event-B_Overview#Control_Constructs_(~~used_in_the Task_body~~) Task body]		\|[http://wiki.event-b.org/index.php/Tasking_Event-B_Overview#Control_Constructs_(used_in_the_Task_body) Task body]
	\|Sequence, Loop, Branch, Event, Output		\|Sequence, Loop, Branch, Event, Output
	\|-		\|-

imported>Andy: /* Tasking Event-B */

2013-08-29T14:55:33Z

Tasking Event-B

← Older revision		Revision as of 14:55, 29 August 2013
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	\|[http://wiki.event-b.org/index.php/Tasking_Event-B_Overview#Tasking_Machines AutoTask], [http://wiki.event-b.org/index.php/Tasking_Event-B_Overview#Shared_Machines Shared], [http://wiki.event-b.org/index.php/Tasking_Event-B_Overview#The_Environ_Machine Environ]		\|[http://wiki.event-b.org/index.php/Tasking_Event-B_Overview#Tasking_Machines AutoTask], [http://wiki.event-b.org/index.php/Tasking_Event-B_Overview#Shared_Machines Shared], [http://wiki.event-b.org/index.php/Tasking_Event-B_Overview#The_Environ_Machine Environ]
	\|-		\|-
	\|[http://wiki.event-b.org/index.php/Tasking_Event-B_Overview#~~Control_Constructs~~ Task body]		\|[http://wiki.event-b.org/index.php/Tasking_Event-B_Overview#Control_Constructs_(used_in_the Task_body) Task body]
	\|Sequence, Loop, Branch, Event, Output		\|Sequence, Loop, Branch, Event, Output
	\|-		\|-

imported>Andy: /* Control Constructs */

2013-08-29T14:53:22Z

Control Constructs

← Older revision		Revision as of 14:53, 29 August 2013
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	=== Control of Program Flow ===		=== Control of Program Flow ===
	At the implementation stage we need to think about controlling the flow of execution; and where interaction with the environment is concerned, how events should be implemented. The following section describes the constructs that we have introduced to facilitate this.		At the implementation stage we need to think about controlling the flow of execution; and where interaction with the environment is concerned, how events should be implemented. The following section describes the constructs that we have introduced to facilitate this.
	==== Control Constructs ====		==== Control Constructs (used in the Task body) ====
	Each Tasking Machine has a ''task body'' which contains the flow control (algorithmic constructs).		Each Tasking Machine has a ''task body'' which contains the flow control (algorithmic constructs).

imported>Andy: /* Tasking Machines */

2013-08-29T14:52:22Z

Tasking Machines

← Older revision		Revision as of 14:52, 29 August 2013
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	* Tasking Machines may be one of the following types:		* Tasking Machines may be one of the following types:
	** AutoTasks - Anonymous Tasks running from start-up.		** AutoTasks - Anonymous Tasks running from start-up.
	** Declared tasks - (Not currently used) A task template relating to an Ada ''tasktype'' declaration.

	''Auto Tasks'' are tasks that will be declared and defined in the ''Main'' procedure of the implementation. The effect of this is that the ''Auto Tasks'' are created when the program first loads, and then activated (made ready to run) before the ''Main'' procedure body runs.		''Auto Tasks'' are tasks that will be declared and defined in the ''Main'' procedure of the implementation. The effect of this is that the ''Auto Tasks'' are created when the program first loads, and then activated (made ready to run) before the ''Main'' procedure body runs.

imported>Andy: /* Tasking Machines */

2013-08-29T14:52:00Z

Tasking Machines

← Older revision		Revision as of 14:52, 29 August 2013
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	==== Tasking Machines ====		==== Tasking Machines ====
	The following constructs relate to Tasking and Environ Machines, and provide implementation details. Timing of periodic tasks is not modelled formally. Tasking and Environ Machines model Ada tasks, so they can be ~~implemented~~ easily in Ada; in C using the pthread library, or in Java using threads.		The following constructs relate to Tasking and Environ Machines, and provide implementation details. Timing of periodic tasks is not modelled formally. Tasking and Environ Machines model Ada tasks, so they can be map easily to Ada; and can implemented in C using the pthread library, or in Java using threads.

	* Tasking Machines may be one of the following types:		* Tasking Machines may be one of the following types: