org.rvpf.processor.engine.executor

Class PipeExecutor

Object

PipeExecutor

All Implemented Interfaces:

Serializable, EngineExecutor

public final class PipeExecutor
extends Object
implements EngineExecutor

Pipe executor.

This executor uses an external program to produce results from inputs. It communicates with this program thru 'pipes' on the program's standard input ('stdin'), output ('stdout') and error ('stderr') streams.

Lines sent to the program's 'stdin'

1. Five integers:
   1. A request ID (long).
   2. The request format version (currently 1).
   3. The number of transform params.
   4. The number of point params.
   5. The number of input values.
2. The requested value description:
   1. The name of the point.
   2. The timestamp.
   3. The state inside '[]'.
   4. The stored value between '"'.
3. A line for each transform param.
4. A line for each point param.
5. A line for each input value containing:
   1. The name of the point.
   2. The timestamp.
   3. The state inside '[]'.
   4. The stored value between '"'.

Lines received from the program's 'stdout'

1. Two integers:
   1. The request ID (long).
   2. A response summary:
      • < 0: No result.
      • = 0: A null result.
      • > 0: The number of result lines.
2. A line for each result value containing:
   1. The name of the point.
   2. The timestamp.
   3. The state inside '[]'.
   4. The value between '"'.

Loop

The program is expected to loop on the requests until it receives a line containing a single field holding only the digit '0'.

Notes

• On each line, the items are separated by spaces.
• A point may be identified by its UUID.
• The timestamp has the ISO 8601 format.
• A missing input is indicated by omitting timestamp, state and value.
• A null state or value is indicated by a missing field.
• The request ID is used for synchronization verification and must be returned verbatim.
• Leading spaces are stripped from the lines received from the process; resulting empty lines are ignored.
• The state is encoded by replacing ']' by '[]' and '[' by ']['.
• The value is encoded by replacing '"' by '""'.

See Also:

Serialized Form

Field Summary

Fields

Modifier and Type	Field and Description
static String	ARG_PARAM An argument for the process.
static String	CHARSET_PARAM The character set for the program execution.
static String	COMMAND_PARAM The operating system command used to activate the process.
static String	DEFAULT_CHARSET Default character set.
static String	DIRECTORY_PARAM Specifies the working directory for the program execution.
static String	KEEP_PROCESS_PARAM The number of milliseconds to keep the process active between invocations.
static String	KILL_DELAY_PARAM The delay before killing a process after closing its input.
static String	PROGRAM_PARAM The path to the program file.
static String	SET_PARAM Sets an environment variable.
static String	TIME_LIMIT_PARAM The time limit to produce a result.

Constructor Summary

Constructors

Constructor and Description
PipeExecutor()

Method Summary

Modifier and Type	Method and Description
void	close() Closes this.
void	disposeContext(Serializable context) Disposes of a context.
List<PointValue>	execute(ResultValue resultValue, String[] params, Serializable context) Executes the processing of a request for a result value.
Serializable	newContext(Params params, Logger logger) Returns a new context.
boolean	setUp(String name, Params params, Config config, Logger logger) Sets up this engine executor.
void	tearDown() Tears down what has been set up.

Methods inherited from class Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

ARG_PARAM

public static final String ARG_PARAM

An argument for the process.

See Also:

Constant Field Values

CHARSET_PARAM

public static final String CHARSET_PARAM

The character set for the program execution.

See Also:

Constant Field Values

COMMAND_PARAM

public static final String COMMAND_PARAM

The operating system command used to activate the process.

See Also:

Constant Field Values

DEFAULT_CHARSET

public static final String DEFAULT_CHARSET

Default character set.

DIRECTORY_PARAM

public static final String DIRECTORY_PARAM

Specifies the working directory for the program execution. Defaults to the current working directory.

See Also:

Constant Field Values

KEEP_PROCESS_PARAM

public static final String KEEP_PROCESS_PARAM

The number of milliseconds to keep the process active between invocations. A negative value means no limit. The default is zero: the process is not kept active.

See Also:

Constant Field Values

KILL_DELAY_PARAM

public static final String KILL_DELAY_PARAM

The delay before killing a process after closing its input.

See Also:

Constant Field Values

PROGRAM_PARAM

public static final String PROGRAM_PARAM

The path to the program file.

See Also:

Constant Field Values

SET_PARAM

public static final String SET_PARAM

Sets an environment variable.

See Also:

Constant Field Values

TIME_LIMIT_PARAM

public static final String TIME_LIMIT_PARAM

The time limit to produce a result.

See Also:

Constant Field Values

Constructor Detail

PipeExecutor

public PipeExecutor()

Method Detail

close

public void close()

Closes this.

Specified by:

close in interface EngineExecutor

disposeContext

public void disposeContext(Serializable context)

Disposes of a context.

Specified by:

disposeContext in interface EngineExecutor

Parameters:

context - The context.

execute

public List<PointValue> execute(ResultValue resultValue,
                                String[] params,
                                Serializable context)
                         throws ServiceNotReadyException

Executes the processing of a request for a result value.

Specified by:

execute in interface EngineExecutor

Parameters:

resultValue - The requested result.

params - Result parameters.

context - The context.

Returns:

A List of point values (null on failure).

Throws:

ServiceNotReadyException

newContext

public Serializable newContext(Params params,
                               Logger logger)

Returns a new context.

Specified by:

newContext in interface EngineExecutor

Parameters:

params - The caller's parameters.

logger - The caller's logger.

Returns:

The new context (null on failure).

setUp

public boolean setUp(String name,
                     Params params,
                     Config config,
                     Logger logger)

Sets up this engine executor.

Specified by:

setUp in interface EngineExecutor

Parameters:

name - The caller's name.

params - The caller's parameters.

config - The configuration.

logger - The caller's logger.

Returns:

True on success.

tearDown

public void tearDown()

Tears down what has been set up.

Specified by:

tearDown in interface EngineExecutor