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Full Discussion: Infinite while loop
Top Forums Shell Programming and Scripting Infinite while loop Post 302370109 by atoponce on Tuesday 10th of November 2009 11:48:56 AM
Old 11-10-2009
Code:
$ true
$ echo $?
0
$ false
$ echo $?
1

That shows the exit code of "true" and "false". As you can see, they both do nothing. One returns a passing exit code, while the other returns a failing exit code. The "while" function wants an argument. It will continue parsing code inside the loop until the argument fails.

Code:
i="0"
while [ $i -lt 4 ]; do
  xterm &
  i=$[$i+1]
done

This piece of code will open four xterm windows. It will only open four, because we set our variable 'i' to 0 and increment it once per loop iteration. When it reaches the value of four, the while condition fails, and the code block will no longer be executed.

So, because "true" does nothing successfully, if you had "while true" in that code block, it would continue and continue to open xterm windows until you ran out of physical resources, and the box could no longer function.

Because "false" does nothing unsuccessfully, if you had "while false" in that code block, it would not even initialize the loop, and immediately exit without opening a single xterm window.
 

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IO::Async::Routine(3pm) 				User Contributed Perl Documentation				   IO::Async::Routine(3pm)

NAME
"IO::Async::Routine" - execute code in an independent sub-process SYNOPSIS
use IO::Async::Routine; use IO::Async::Channel; use IO::Async::Loop; my $loop = IO::Async::Loop->new; my $nums_ch = IO::Async::Channel->new; my $ret_ch = IO::Async::Channel->new; my $routine = IO::Async::Routine->new( channels_in => [ $nums_ch ], channels_out => [ $ret_ch ], code => sub { my @nums = @{ $nums_ch->recv }; my $ret = 0; $ret += $_ for @nums; # Can only send references $ret_ch->send( $ret ); }, on_finish => sub { say "The routine aborted early - $_[-1]"; $loop->stop; }, ); $loop->add( $routine ); $nums_ch->send( [ 10, 20, 30 ] ); $ret_ch->recv( on_recv => sub { my ( $ch, $totalref ) = @_; say "The total of 10, 20, 30 is: $$totalref"; $loop->stop; } ); $loop->run; DESCRIPTION
This subclass of IO::Async::Process contains a body of code and executes it in a sub-process, allowing it to act independently of the main program. Once set up, all communication with the code happens by values passed into or out of the Routine via IO::Async::Channel objects. Because the code running inside the Routine runs within its own process, it is isolated from the rest of the program, in terms of memory, CPU time, and other resources, and perhaps most importantly in terms of control flow. The code contained within the Routine is free to make blocking calls without stalling the rest of the program. This makes it useful for using existing code which has no option not to block within an "IO::Async"-based program. To create asynchronous wrappers of functions that return a value based only on their arguments, and do not generally maintain state within the process it may be more convenient to use an IO::Async::Function instead, which uses an "IO::Async::Routine" to contain the body of the function and manages the Channels itself. PARAMETERS
The following named parameters may be passed to "new" or "configure": channels_in => ARRAY of IO::Async::Channel ARRAY reference of "IO::Async::Channel" objects to set up for passing values in to the Routine. channels_out => ARRAY of IO::Async::Channel ARRAY reference of "IO::Async::Channel" objects to set up for passing values out of the Routine. code => CODE CODE reference to the body of the Routine, to execute once the channels are set up. METHODS
This class provides no additional methods, other than those provided by IO::Async::Process. AUTHOR
Paul Evans <leonerd@leonerd.org.uk> perl v5.14.2 2012-10-24 IO::Async::Routine(3pm)
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