DaemonLost class - Revision history

JAL: minor cleanup

2014-11-18T22:16:19Z

minor cleanup

← Older revision		Revision as of 22:16, 18 November 2014
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	The <var>DaemonLost</var> exception class indicates that a daemon thread associated with a daemon object was lost, most probably because of a user restart.		The <var>DaemonLost</var> exception class indicates that a daemon thread associated with a daemon object was lost, most probably because of a user restart.

	The <var>[[Run (Daemon function)\|Run]]</var> function of the <var>[[Daemon_class\|Daemon]]</var> system class is an example of a system method that automatically throws a <var>DaemonLost</var> exception. For more information about catching a thrown exception, see [[Exceptions#Try and Catch\|"Try and Catch"]].		The <var>[[Run (Daemon function)\|Run]]</var> function of the <var>[[Daemon_class\|Daemon]]</var> system class is an example of a system method that automatically throws a <var>DaemonLost</var> exception. For more information about catching a thrown exception, see [[Exceptions#Try and Catch\|Try and Catch]].

	The following example shows a <var>Try</var> and <var>Catch</var> of a <var>DaemonLost</var> exception. The daemon request is contrived to produce a user restart to demonstrate <var>DaemonLost</var> exception output.		The following example shows a <var>Try</var> and <var>Catch</var> of a <var>DaemonLost</var> exception. The daemon request is contrived to produce a user restart to demonstrate <var>DaemonLost</var> exception output.
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	The methods in the class are described in the subsections that follow. In addition:		The methods in the class are described in the subsections that follow. In addition:
	<ul>		<ul>
	<li>[[Notation conventions for methods~~\|"Notation conventions for methods"~~]] has information		<li>[[Notation conventions for methods]] has information about the conventions followed. </li>
	about the conventions followed.		<li>[[DaemonLost methods syntax]] is a single page that contains the syntax diagrams of all the methods in the class. </li>
	<li>[[DaemonLost methods syntax~~\|"DaemonLost methods syntax"~~]] is a single page that contains the syntax diagrams of all the methods in the class.
	</ul>		</ul>

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	====Syntax terms====		====Syntax terms====
	<table ~~class="syntaxTable"~~>		<table>
	<tr><th>%sl</th>		<tr><th>%sl</th>
	<td>This <var>Stringlist</var> contains a copy of the daemon thread's last output. The <var>Stringlist</var> may be empty, that is, have no items.		<td>This <var>Stringlist</var> contains a copy of the daemon thread's last output. The <var>Stringlist</var> may be empty, that is, have no items.
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	===Syntax===		===Syntax===
	{{Template:DaemonLost:New syntax}}		{{Template:DaemonLost:New syntax}}

	====Syntax terms====		====Syntax terms====
	<table ~~class="syntaxTable"~~>		<table>

	<tr><th>%daemonLost</th>		<tr><th>%daemonLost</th>
	<td>A reference to an instance of a <var>DaemonLost</var> object.		<td>A reference to an instance of a <var>DaemonLost</var> object.

JAL at 21:42, 21 November 2012

2012-11-21T21:42:29Z

New page

__NOTOC__
The <var>DaemonLost</var> exception class indicates that a daemon thread associated with a daemon object was lost, most probably because of a user restart.

The <var>[[Run (Daemon function)|Run]]</var> function of the <var>[[Daemon_class|Daemon]]</var> system class is an example of a system method that automatically throws a <var>DaemonLost</var> exception. For more information about catching a thrown exception, see [[Exceptions#Try and Catch|"Try and Catch"]].

The following example shows a <var>Try</var> and <var>Catch</var> of a <var>DaemonLost</var> exception. The daemon request is contrived to produce a user restart to demonstrate <var>DaemonLost</var> exception output.
<p class="code">begin
%dmn is object daemon
%sl is object [[Stringlist class|stringlist]]
%daemonLost is object daemonLost

%dmn = new
%sl = new
[[Text_and_Html_statements#toOption|text to]] %sl
begin
print 'Rosebud'
end
begin
end text

try %dmn:run(%sl)
catch daemonLost to %daemonLost
[[PrintText statement|printText]] Daemon died! Its last words were:
%daemonLost:daemonOutput:print
end try
end
</p>

The result of the preceding request shows the daemon output that was stored in the exception:
<p class="output">Daemon died! Its last words were:
ROSEBUD
</p>
<b>Note:</b> It is necessary to declare the exception object in the main thread of the program, but instantiating it is taken care of by the <var>[[Daemon_class|Daemon]]</var> class <var>[[Run (Daemon function)|Run]]</var> method.

A request cancellation does not cause the daemon thread to go away, so it does not produce a <var>DaemonLost</var> exception. Consequently, using the error count on the last command may be an adequate way
for your application to check for a request cancellation:
<p class="code">begin
%dmn is object daemon
%prog is object stringlist

%dmn = new
%prog = new
text to %prog
begin
assert 1 eq 2
end
end text

try %dmn:run(%prog)
if %dmn:lastCommandErrorCount then
print 'Error in daemon!'
end if
catch daemonLost
printText Caught a DaemonLost.
end try
end
</p>

To produce a <var>DaemonLost</var> exception for a user-created method, you would issue a <var class="product">User Language</var> <var>[[Exceptions#Throwing exceptions|Throw]]</var> statement from within the method, and you must catch it in the code that called the method. Because this exception is tailored to <var>daemon</var> execution by the system <var>Run</var> method, you are not likely to throw it from a user method, unless you want the method to <var>Catch</var> and then <var>Throw</var> the exception to the code that called the method. For example, your method might contain code like this:
<p class="code">%dLost is object daemonLost
try %dmn:run(%whatever)
catch daemonLost to %dlost
throw %dlost
end try
</p>

And the code that calls the method might contain:
<p class="code">%daemLost is object daemonLost
try %obj:mymethod
catch daemonLost to %daemLost
printText Daemon lost!
%daemLost:daemonOutput:print
end try
</p>

==The DaemonLost methods==
{{Template:List of DaemonLost methods}}

The methods in the class are described in the subsections that follow. In addition:
<ul>
<li>[[Notation conventions for methods|"Notation conventions for methods"]] has information
about the conventions followed.
<li>[[DaemonLost methods syntax|"DaemonLost methods syntax"]] is a single page that contains the syntax diagrams of all the methods in the class.
</ul>

==DaemonOutput property==
{{Template:DaemonLost:DaemonOutput subtitle}}

This <var>[[Classes and Objects#readWrite|ReadOnly]]</var> property returns a <var>[[Stringlist|Stringlist]]</var> that contains a copy of the output of the last stream the daemon thread was running before it was lost (probably restarted). The contents of this stringlist might be useful in determining why the daemon thread was restarted.

===Syntax===
{{Template:DaemonLost:DaemonOutput syntax}}

====Syntax terms====
<table class="syntaxTable">
<tr><th>%sl</th>
<td>This <var>Stringlist</var> contains a copy of the daemon thread's last output. The <var>Stringlist</var> may be empty, that is, have no items.
</td></tr>

<tr><th>daemonLost</th>
<td>A reference to an instance of a <var>[[DaemonLost_class|DaemonLost]]</var> object.
</td></tr></table>

==New constructor==
{{Template:DaemonLost:New subtitle}}

This <var>Constructor</var> generates an instance of a <var>[[DaemonLost_class|DaemonLost]]</var> exception. As shown below, the optional argument of the <var>New</var> method is a setting of the <var>[[DaemonOutput_(DaemonLost_property)|DaemonOutput]]</var> property.

===Syntax===
{{Template:DaemonLost:New syntax}}
====Syntax terms====
<table class="syntaxTable">

<tr><th>%daemonLost</th>
<td>A reference to an instance of a <var>DaemonLost</var> object.
</td></tr>

<tr><th><var>[%(DaemonLost):]</var></th>
<td>The class name in parentheses denotes a <var>[[Notation conventions for methods#Constructors|Constructor]]</var>.</td></tr>

<tr><th><var>DaemonOutput</var></th>
<td>This optional, but [[Methods#Named parameters|name required]], parameter specifies the <var>Stringlist</var> (<var class="term">stringlist</var>) to be assigned to the <var>DaemonLost</var> exception object's <var>DaemonOutput</var> property when a daemon thread is lost.
</td></tr></table>

[[Category:System exception classes]]

Dme at 14:05, 13 September 2012

2012-09-13T14:05:07Z

← Older revision		Revision as of 14:05, 13 September 2012
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	%dmn = new		%dmn = new
	%sl = new		%sl = new
	[[Text_and_Html_statements#~~The_HTML_or_TEXT_statement~~\|text to]] %sl		[[Text_and_Html_statements#toOption\|text to]] %sl
	begin		begin
	print 'Rosebud'		print 'Rosebud'

JAL2 at 17:47, 7 August 2012

2012-08-07T17:47:54Z

← Older revision		Revision as of 17:47, 7 August 2012
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	</td></tr></table>		</td></tr></table>

	~~<h2>~~New constructor~~</h2>~~		==New constructor==
	{{Template:DaemonLost:New subtitle}}		{{Template:DaemonLost:New subtitle}}

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	<h4>Syntax terms</h4>		<h4>Syntax terms</h4>
	<table class="syntaxTable">		<table class="syntaxTable">

	<tr><th>%daemonLost</th>		<tr><th>%daemonLost</th>
	<td>A reference to an instance of a <var>DaemonLost</var> object.		<td>A reference to an instance of a <var>DaemonLost</var> object.
	</td></tr>		</td></tr>
	<tr><th><var>%(DaemonLost)</var></th>
			<tr><th><var>[%(DaemonLost):]</var></th>
	<td>The class name in parentheses denotes a <var>[[Notation conventions for methods#Constructors\|Constructor]]</var>.</td></tr>		<td>The class name in parentheses denotes a <var>[[Notation conventions for methods#Constructors\|Constructor]]</var>.</td></tr>

	<tr><th><var>DaemonOutput</var></th>		<tr><th><var>DaemonOutput</var></th>
	<td>This optional, but [[Methods#Named parameters\|name required]], parameter specifies the <var>Stringlist</var> (<var class="term">stringlist</var>) to be assigned to the <var>DaemonLost</var> exception object's <var>DaemonOutput</var> property when a daemon thread is lost.		<td>This optional, but [[Methods#Named parameters\|name required]], parameter specifies the <var>Stringlist</var> (<var class="term">stringlist</var>) to be assigned to the <var>DaemonLost</var> exception object's <var>DaemonOutput</var> property when a daemon thread is lost.

JAL2 at 20:54, 27 July 2011

2011-07-27T20:54:38Z

← Older revision		Revision as of 20:54, 27 July 2011
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	{{Template:DaemonLost:New subtitle}}		{{Template:DaemonLost:New subtitle}}

	This ~~constructor~~ generates an instance of a <var>[[DaemonLost_class\|DaemonLost]]</var> exception. As shown below, the optional argument of the <var>New</var> method is a setting of the <var>[[DaemonOutput_(DaemonLost_property)\|DaemonOutput]]</var> property.		This <var>Constructor</var> generates an instance of a <var>[[DaemonLost_class\|DaemonLost]]</var> exception. As shown below, the optional argument of the <var>New</var> method is a setting of the <var>[[DaemonOutput_(DaemonLost_property)\|DaemonOutput]]</var> property.

	<h3>Syntax</h3>		<h3>Syntax</h3>
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	</td></tr>		</td></tr>
	<tr><th><var>%(DaemonLost)</var></th>		<tr><th><var>%(DaemonLost)</var></th>
	<td>The class name in parentheses denotes a ~~shared method~~.</td></tr>		<td>The class name in parentheses denotes a <var>[[Notation conventions for methods#Constructors\|Constructor]]</var>.</td></tr>
	<tr><th><var>DaemonOutput</var></th>		<tr><th><var>DaemonOutput</var></th>
	<td>This optional, but [[Methods#Named parameters\|name required]], parameter specifies the <var>Stringlist</var> (<var class="term">stringlist</var>) to be assigned to the <var>DaemonLost</var> exception object's <var>DaemonOutput</var> property when a daemon thread is lost.		<td>This optional, but [[Methods#Named parameters\|name required]], parameter specifies the <var>Stringlist</var> (<var class="term">stringlist</var>) to be assigned to the <var>DaemonLost</var> exception object's <var>DaemonOutput</var> property when a daemon thread is lost.

JAL2 at 22:27, 17 May 2011

2011-05-17T22:27:04Z

← Older revision		Revision as of 22:27, 17 May 2011
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	This <var>[[Classes and Objects#readWrite\|ReadOnly]]</var> property returns a <var>[[Stringlist\|Stringlist]]</var> that contains a copy of the output of the last stream the daemon thread was running before it was lost (probably restarted). The contents of this stringlist might be useful in determining why the daemon thread was restarted.		This <var>[[Classes and Objects#readWrite\|ReadOnly]]</var> property returns a <var>[[Stringlist\|Stringlist]]</var> that contains a copy of the output of the last stream the daemon thread was running before it was lost (probably restarted). The contents of this stringlist might be useful in determining why the daemon thread was restarted.

	<h4>Syntax</h4>		<h3>Syntax</h3>
	{{Template:DaemonLost:DaemonOutput syntax}}		{{Template:DaemonLost:DaemonOutput syntax}}
	<h4>Syntax terms</h4>		<h4>Syntax terms</h4>
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	<h2>New constructor</h2>		<h2>New constructor</h2>
	{{Template:DaemonLost:New subtitle}}		{{Template:DaemonLost:New subtitle}}

	This constructor generates an instance of a <var>[[DaemonLost_class\|DaemonLost]]</var> exception. As shown below, the optional argument of the <var>New</var> method is a setting of the <var>[[DaemonOutput_(DaemonLost_property)\|DaemonOutput]]</var> property.		This constructor generates an instance of a <var>[[DaemonLost_class\|DaemonLost]]</var> exception. As shown below, the optional argument of the <var>New</var> method is a setting of the <var>[[DaemonOutput_(DaemonLost_property)\|DaemonOutput]]</var> property.

	<h4>Syntax</h4>		<h3>Syntax</h3>
	{{Template:DaemonLost:New syntax}}		{{Template:DaemonLost:New syntax}}
	<h4>Syntax terms</h4>		<h4>Syntax terms</h4>

JAL2 at 14:53, 10 May 2011

2011-05-10T14:53:58Z

← Older revision		Revision as of 14:53, 10 May 2011
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	<td>The class name in parentheses denotes a shared method.</td></tr>		<td>The class name in parentheses denotes a shared method.</td></tr>
	<tr><th><var>DaemonOutput</var></th>		<tr><th><var>DaemonOutput</var></th>
	<td>This optional, but [[Methods#Named parameters\|name required]], parameter specifies the <var>Stringlist</var> (<var class="term">stringlist</var>) to be assigned to the <var>DaemonLost</var> exception object's <var>~~[[DaemonOutput_(DaemonLost_property)\|~~DaemonOutput]]</var> property when a daemon thread is lost.		<td>This optional, but [[Methods#Named parameters\|name required]], parameter specifies the <var>Stringlist</var> (<var class="term">stringlist</var>) to be assigned to the <var>DaemonLost</var> exception object's <var>DaemonOutput</var> property when a daemon thread is lost.
	</td></tr></table>		</td></tr></table>


	[[Category:System exception classes]]		[[Category:System exception classes]]

JAL2 at 14:50, 10 May 2011

2011-05-10T14:50:51Z

← Older revision		Revision as of 14:50, 10 May 2011
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	The <var>[[Run (Daemon function)\|Run]]</var> function of the <var>[[Daemon_class\|Daemon]]</var> system class is an example of a system method that automatically throws a <var>DaemonLost</var> exception. For more information about catching a thrown exception, see "[[Try and Catch]]".		The <var>[[Run (Daemon function)\|Run]]</var> function of the <var>[[Daemon_class\|Daemon]]</var> system class is an example of a system method that automatically throws a <var>DaemonLost</var> exception. For more information about catching a thrown exception, see "[[Try and Catch]]".

	The following example shows a ~~"[[~~Try and Catch~~]]"~~ of a <var>DaemonLost</var> exception. The daemon request is contrived to produce a user restart to demonstrate <var>DaemonLost</var> exception output.		The following example shows a <var>Try</var> and <var>Catch</var> of a <var>DaemonLost</var> exception. The daemon request is contrived to produce a user restart to demonstrate <var>DaemonLost</var> exception output.
	<p class="code">begin		<p class="code">begin
	%dmn is object daemon		%dmn is object daemon
Line 38:		Line 38:
	<p class="code">begin		<p class="code">begin
	%dmn is object daemon		%dmn is object daemon
	%prog is object ~~[[Stringlist class\|~~stringlist]]		%prog is object stringlist

	%dmn = new		%dmn = new
	%prog = new		%prog = new
	~~[[Text_and_Html_statements#The_HTML_or_TEXT_statement\|~~text to]] %prog		text to %prog
	begin		begin
	assert 1 eq 2		assert 1 eq 2
Line 48:		Line 48:
	end text		end text

	[[try]] %dmn:run(%prog)		try %dmn:run(%prog)
	if %dmn:lastCommandErrorCount then		if %dmn:lastCommandErrorCount then
	print 'Error in daemon!'		print 'Error in daemon!'
	end if		end if
	[[catch]] daemonLost		catch daemonLost
	~~[[PrintText statement\|~~printText]] Caught a DaemonLost.		printText Caught a DaemonLost.
	end try		end try
	end		end
Line 60:		Line 60:
	To produce a <var>DaemonLost</var> exception for a user-created method, you would issue a <var class="product">User Language</var> <var>[[Throw]]</var> statement from within the method, and you must catch it in the code that called the method. Because this exception is tailored to <var>daemon</var> execution by the system <var>Run</var> method, you are not likely to throw it from a user method, unless you want the method to <var>[[Catch]]</var> and then <var>Throw</var> the exception to the code that called the method. For example, your method might contain code like this:		To produce a <var>DaemonLost</var> exception for a user-created method, you would issue a <var class="product">User Language</var> <var>[[Throw]]</var> statement from within the method, and you must catch it in the code that called the method. Because this exception is tailored to <var>daemon</var> execution by the system <var>Run</var> method, you are not likely to throw it from a user method, unless you want the method to <var>[[Catch]]</var> and then <var>Throw</var> the exception to the code that called the method. For example, your method might contain code like this:
	<p class="code">%dLost is object daemonLost		<p class="code">%dLost is object daemonLost
	[[try]] %dmn:run(%whatever)		try %dmn:run(%whatever)
	[[catch]] daemonLost to %dlost		catch daemonLost to %dlost
	throw %dlost		throw %dlost
	end try		end try
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	And the code that calls the method might contain:		And the code that calls the method might contain:
	<p class="code">%daemLost is object daemonLost		<p class="code">%daemLost is object daemonLost
	[[try]] %obj:mymethod		try %obj:mymethod
	[[catch]] daemonLost to %daemLost		catch daemonLost to %daemLost
	printText Daemon lost!		printText Daemon lost!
	%daemLost:daemonOutput:print		%daemLost:daemonOutput:print

JAL2 at 00:15, 10 May 2011

2011-05-10T00:15:52Z

← Older revision		Revision as of 00:15, 10 May 2011
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	ROSEBUD		ROSEBUD
	</p>		</p>
	<b>Note:</b> It is necessary to declare the exception object in the main thread of the program, but instantiating it is taken care of by the <var>[[~~Run (~~Daemon ~~function)\|Run~~]]</var> <var>[[~~Daemon_class~~\|~~Daemon~~]]</var> method.		<b>Note:</b> It is necessary to declare the exception object in the main thread of the program, but instantiating it is taken care of by the <var>[[Daemon_class\|Daemon]]</var> class <var>[[Run (Daemon function)\|Run]]</var> method.

	A request cancellation does not cause the daemon thread to go away, so it does not produce a <var>DaemonLost</var> exception. Consequently, using the error count on the last command may be an adequate way		A request cancellation does not cause the daemon thread to go away, so it does not produce a <var>DaemonLost</var> exception. Consequently, using the error count on the last command may be an adequate way
Line 58:		Line 58:
	</p>		</p>

	To produce a <var>DaemonLost</var> exception for a user-created method, you would issue a User Language ~~Language~~ <var>[[Throw]]</var> statement from within the method, and you must catch it in the code that called the method. Because this exception is tailored to <var>daemon</var> execution by the system <var>Run</var> method, you are not likely to throw it from a user method, unless you want the method to <var>[[~~Catach~~]]</var> and then <var>Throw</var> the exception to the code that called the method. For example, your method might contain code like this:		To produce a <var>DaemonLost</var> exception for a user-created method, you would issue a <var class="product">User Language</var> <var>[[Throw]]</var> statement from within the method, and you must catch it in the code that called the method. Because this exception is tailored to <var>daemon</var> execution by the system <var>Run</var> method, you are not likely to throw it from a user method, unless you want the method to <var>[[Catch]]</var> and then <var>Throw</var> the exception to the code that called the method. For example, your method might contain code like this:
	<p class="code">%dLost is object daemonLost		<p class="code">%dLost is object daemonLost
	[[try]] %dmn:run(%whatever)		[[try]] %dmn:run(%whatever)

JAL2 at 00:12, 10 May 2011

2011-05-10T00:12:19Z

← Older revision		Revision as of 00:12, 10 May 2011
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	</td></tr></table>		</td></tr></table>

	<~~h2New~~ constructor</h2>		<h2>New constructor</h2>
	{{Template:DaemonLost:New subtitle}}		{{Template:DaemonLost:New subtitle}}
	This constructor generates an instance of a <var>[[DaemonLost_class\|DaemonLost]]</var> exception. As shown below, the optional argument of the <var>New</var> method is a setting of the <var>[[DaemonOutput_(DaemonLost_property)\|DaemonOutput]]</var> property.		This constructor generates an instance of a <var>[[DaemonLost_class\|DaemonLost]]</var> exception. As shown below, the optional argument of the <var>New</var> method is a setting of the <var>[[DaemonOutput_(DaemonLost_property)\|DaemonOutput]]</var> property.