New signal

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4D v20.6

New signal


New signal {( description )} -> Function result

Parameter	Type	Description
description	Text	Description for the signal
Function result	Object	Native object encapsulating the signal

Description

The New signal command creates a signal object.

A signal is a shared object which can be passed as parameter from a worker or process to another worker or process, so that:

the called worker/process can update the signal object after specific processing has completed
the calling worker/process can stop its execution and wait until the signal is updated, without consuming any cpu resources.

Optionally, in the description parameter you can pass a custom text describing the signal. This text can also be defined after signal creation.

Since the signal object is a shared object (see Shared objects and shared collections), it can also be used to maintain user properties, including the signal.description property, by calling the Use...End use structure.

Returned value

The returned signal object contains the following properties and methods:

Property	Type	Description
signal.signaled	Boolean	(read-only property) false at signal creation. Becomes true when the signal.trigger( ) method is called.
signal.description	Text	Custom description of the signal, if any.

Method	Description
signal.wait( )	Wait for the signal (calling process/worker)
signal.trigger( )	Trigger the signal (called process/worker)

Example

Here is a typical example of a worker that sets a signal:

 C_OBJECT($signal)

 $signal:=New signal("This is my first signal")

 

 CALL WORKER("myworker";"doSomething";$signal)

 $signaled:=$signal.wait(1) //wait for 1 second max

 

 If($signaled)

    ALERT("myworker finished the work. Result: "+$signal.myresult)

 Else

    ALERT("myworker has not finished in less than 1s")

 End if

The "doSomething" method could be like:

 C_OBJECT($1)

  //any processing

  //...

 Use($1)

    $1.myresult:=$processingResult  //return the result

 End use

 $1.trigger() // The work is finished