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Re^3: Is it possible to create a single Hash-of-Hash.. with multiple threads..

by BrowserUk (Pope)
on Apr 25, 2014 at 10:21 UTC ( #1083769=note: print w/ replies, xml ) Need Help??


in reply to Re^2: Is it possible to create a single Hash-of-Hash.. with multiple threads..
in thread Is it possible to create a single Hash-of-Hash.. with multiple threads..

Perl Threads implementation so far, seems very inadequate - it is good for primary school student exhibiting how parallel programming works.

That is a wrong conclusion drawn through a lack of understanding.

If you would care to describe your application in detail -- not just generics, but rather scales and reasons; with examples of data and processing requirements -- then you would (probably) get help with finding definitive, practical and efficient solutions to those requirements.

Your OP asks a simplistic question with an obvious answer: Yes, of course a multi-level hash can be constructed using multiple threads. It is simple and trivial:

#! perl -slw use strict; use threads; use threads::shared; sub displayHash { my( $ref, $pad ) = @_; return "\n" unless keys %{ $ref }; my $buf = ''; for my $key ( sort keys %{ $ref } ) { $buf .= "$pad" if length $buf; $buf .= "{$key}" . displayHash( $ref->{ $key }, $pad . ' ' ) +; } return $buf; } sub worker { my( $ref, $reps ) = @_; for( 1 .. $reps ) { my $copyRef = $ref; for my $step ( map chr( 97 + rand 26 ), 1 .. int( rand 10 ) ) +{ if( exists $copyRef->{ $step } ) { $copyRef = $copyRef->{ $step }; } else { lock %{ $copyRef }; $copyRef = $copyRef->{ $step } = &share( {} ); } } } } our $REPS //= 20; our $THREADS //= 4; my %HoHos : shared; my @threads = map threads->create( \&worker, \%HoHos, $REPS ), 1 .. $T +HREADS; $_->join for @threads; print displayHash( \%HoHos, '' ); __END__ C:\test>junk91 -REPS=7 {b}{l}{w}{g} {d}{t}{k}{f}{g}{g}{g}{i}{j} {f}{j}{v} {g}{s}{g}{h}{g} {i}{f}{j}{r}{m}{v}{u}{v}{b} {k}{d}{f}{q}{k} {z}{t}{m}{h}{e}{i} {m}{b}{l} {l}{u}{p}{t}{d}{h} {q}{k}{y} {n}{f}{u}{v}{z}{z}{l} {o}{f} {p}{u}{s}{w}{n}{t} {q}{h} {y}{k}{d}{l}{a}{n}{a}{i} {r}{q}{t}{g} {v}{o}{n}{x}{b}{g}{c} {w}{a} {y}{a} {d}{y}{j} {z}{a}{p}{t}{i}{r}{t} {y}{i}{g}{c}{v}{z}{z}{k}

But, it is also probably not very helpful to your real application.


With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday'
Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
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Comment on Re^3: Is it possible to create a single Hash-of-Hash.. with multiple threads..
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Re^4: Is it possible to create a single Hash-of-Hash.. with multiple threads..
by gsat (Initiate) on May 02, 2014 at 16:18 UTC

    Dear Monk BrowserUk! Please take a bow!!

    Thank You so much - for enlightening me :) Indeed - it was my lack of understanding.

    I have found this entire discussion from everybody - very helpful.

    -=-=-=-=-=-=-=-

    Now, I need more :) It seems - me and my code is tired of doing so many .. if exists.. else share.. kinda additives before I do any structure change - and I think no way to avoid that. Now a couple of Questions here:

    Q1. Is there any easier method?

    Q2. Is it possible to grow a local tree or branch data-structure, then create a shared_clone - and graft the new tree to s sub-branch of main shared tree?

    Q3. I have few subroutines to be called many times - based on data - from inside my thread_worker. So far I am lacking depth in understanding or visualizing - how/when multiple threads work on different set of data, while calling a subroutine - does the code-inside-subroutine-block gets a replicated inside the thread uniquely? - else how the sanity is retained? - sorry if I am asking too basic question - maybe it is the case, I am confused - and not clear enough - where is my confusion too..

    Q4. Inside subroutine - do I have to use every variable as local and not-shared?

    Thanks a lot! Again & Again!

      1. No.

        You can replace:

        if( exists $copyRef->{ $step } ) { $copyRef = $copyRef->{ $step }; } else { lock %{ $copyRef }; $copyRef = $copyRef->{ $step } = &share( {} ); }

        With:

        lock %{ $copyRef }; $copyRef = $copyRef->{ $step } //= &share( {} )

        Which is more compact, but not easier nor more efficient.

      2. Yes.

        Two possibilities:

        1. You can build a normal (non-shared) subhash and when complete, use threads::shared::shared_clone() to make a shared copy of it and assign a reference to the copy to a key/value pair in the main shared hash:
          ... my %subhash; ... # populate it lock %mainSharedHash; $mainSharedHash{ $key } = shared_clone( \%subhash ); ...
        2. You can create a shared subhash and assign a ref to it without needing to copy:
          ... my %subhash :shared: ... # populate it lock %mainSharedHash; $mainSharedHash{ $key } = \%subhash;
      3. I do not understand the question.

        You'll get better answers if you describe your actual application. Ie. Real requirements garner working responses.

      4. Again, your question makes no sense.

        In a subroutine (or anywhere else), you can use unshared variables and/or shared variables as required.


      With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday'
      Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
      "Science is about questioning the status quo. Questioning authority".
      In the absence of evidence, opinion is indistinguishable from prejudice.

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