http://qs321.pair.com?node_id=11140473


in reply to making a loop script with a remote URL call faster

I'm with LanX, I don't really see how it would make sense to iterate the loop multiple times if price doesn't change, but if you really want a tight loop, everyone loves threads: 

#!/usr/bin/perl -w
use strict; use warnings;

use threads;
use threads::shared;

my $PRICING :shared = 0;
my $RUNNING :shared = 1;


sub price_thread {
    while ($RUNNING) {
        # Local variable to limit lock time.
        # Catch errors in eval
        my $pricing = eval {
            # Net::Curl to remote URL... request here.
            my $val = 1000 * rand(); # [from net::curl]
            # ... more?
            # last line will go to $pricing and $pricing gets undef on
+ exception
            $val
        };

        do {
            lock($PRICING);
            $PRICING = $pricing;
        };

        # Optional pause between requests:
        sleep 60;
    }
}

sub main_loop {
    # Local variable to limit lock time and prevent changes mid-comput
+ation
    my $pricing = 0;
    while ($RUNNING) {
        do {
            lock($PRICING);
            $pricing = $PRICING;
        };

        # Optional - I don't know what you are doing with pricing, you
+ might want
        # to use 0 or undef to signal a request error (i.e., out-of-da
+te data).
        next if !defined($pricing) or $pricing == 0;

        # Do something with $pricing;
        print "$pricing\n";
        sleep 1; # Work simulation

        # return if QUIT CONDITION;
    }
}

my $thr = threads->create(\&price_thread);
eval { main_loop() };
$RUNNING = 0;
$thr->join();

[download]

Good Day,
    Dean

Replies are listed 'Best First'.
Re^2: making a loop script with a remote URL call faster
by marioroy (Prior) on Jul 08, 2022 at 02:05 UTC

    The following is duelafn's demonstration converted to using MCE::Hobo and MCE::Shared and runs in Perl lacking threads support. Locking is handled automatically behind the scene. I updated the code to run at each interval period.

    Update: Use monotonic clock.

    #!/usr/bin/perl -w
use strict; use warnings;

use MCE::Hobo;
use MCE::Shared;
use Time::HiRes qw(time sleep);

# Use monotonic clock if available.
use constant CLOCK_MONOTONIC => eval {
    Time::HiRes::clock_gettime( Time::HiRes::CLOCK_MONOTONIC() );
    1;
};
sub _time {
    ( CLOCK_MONOTONIC )
      ? Time::HiRes::clock_gettime( Time::HiRes::CLOCK_MONOTONIC() )
      : Time::HiRes::time();
}

my $DEBUG = 1;
my $INTERVAL = $DEBUG ? 3.0 : 60.0;

my $PRICING = MCE::Shared->scalar(0);
my $RUNNING = MCE::Shared->scalar(1);

sub price_thread {
    my $next_interval = _time() + $INTERVAL;
    while ($RUNNING->get()) {
        printf("# TIME %.3f\n", _time()) if $DEBUG;
        # Local variable to limit lock time.
        # Catch errors in eval
        my $pricing = eval {
            # Net::Curl to remote URL... request here.
            my $val = 1000 * rand(); # [from net::curl]
            # ... more?
            # last line will go to $pricing and $pricing gets undef on
+ exception
            $val
        };

        $PRICING->set($pricing);

        # Pause between requests:
        my $time = _time();
        if ($time > $next_interval) {
            # Wait till next interval if curl time is greater than $IN
+TERVAL.
            $next_interval += $INTERVAL while $next_interval < $time;
        }
        sleep $next_interval - $time;
        $next_interval += $INTERVAL;
    }
}

sub main_loop {
    # Local variable to limit lock time and prevent changes mid-comput
+ation
    my $pricing = 0;
    while ($RUNNING->get()) {
        $pricing = $PRICING->get();

        # Optional - I don't know what you are doing with pricing, you
+ might want
        # to use 0 or undef to signal a request error (i.e., out-of-da
+te data).
        next if !defined($pricing) or $pricing == 0;

        # Do something with $pricing;
        print "$pricing\n";
        sleep 1; # Work simulation

        # return if QUIT CONDITION;
    }
}

my $thr = MCE::Hobo->create({ void_context => 1 }, \&price_thread);
eval { main_loop() };
$RUNNING->set(0);
$thr->join();

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