Module: HybridPlatformsConductor::ParallelThreads

Included in:
HpcPlugins::Cmdb::HostIp, HpcPlugins::Cmdb::HostKeys, NodesHandler, ServicesHandler, TestsRunner
Defined in:
lib/hybrid_platforms_conductor/parallel_threads.rb

Overview

Provide utilities to handle parallel threads

Instance Method Summary collapse

Instance Method Details

#for_each_element_in(list, parallel: false, nbr_threads_max: nil, progress: 'Process') ⇒ Object

Iterate over a list of objects. Provide a mechanism to multithread this iteration (in such case the iterating code has to be thread-safe). In case of multithreaded run, a progress bar is being displayed.

Parameters

  • list (Array<Object>): List of objects to iterate over

  • parallel (Boolean): Iterate in a multithreaded way? [default: false]

  • nbr_threads_max (Integer or nil): Maximum number of threads to be used in case of parallel, or nil for no limit [default: nil]

  • progress (String or nil): Name of a progress bar to follow the progression, or nil for no progress bar [default: ‘Progress’]

  • Proc: The code called for each node being iterated on.

    • Parameters

      • element (Object): The object



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# File 'lib/hybrid_platforms_conductor/parallel_threads.rb', line 20

def for_each_element_in(list, parallel: false, nbr_threads_max: nil, progress: 'Process')
  if parallel
    # Threads to wait for
    threads_to_join = []
    # Spread elements evenly among the threads.
    # Use a shared pool of elements to be handled by threads.
    pools = {
      to_process: list.dup,
      processing: [],
      processed: []
    }
    nbr_total = list.size
    # Protect access to the pools using a mutex
    pools_semaphore = Mutex.new
    # Spawn the threads, each one responsible for handling its list
    (nbr_threads_max.nil? || nbr_threads_max > nbr_total ? nbr_total : nbr_threads_max).times do
      threads_to_join << Thread.new do
        # As exceptions are logged anyway whatever the Thread setting is, only turn it on for debug.
        # That will keep tests execution cleaner.
        Thread.current.report_on_exception = log_debug?
        begin
          loop do
            # Modify the list while processing it, so that reporting can be done.
            element = nil
            pools_semaphore.synchronize do
              element = pools[:to_process].shift
              pools[:processing] << element unless element.nil?
            end
            break if element.nil?
            begin
              yield element
            ensure
              pools_semaphore.synchronize do
                pools[:processing].delete(element)
                pools[:processed] << element
              end
            end
          end
        rescue
          log_error "Unhandled exception occurred in thread #{Thread.current.object_id}: #{$!}\n#{$!.backtrace.join("\n")}"
          raise
        end
      end
    end
    if progress
      # Here the main thread just reports progression
      nbr_to_process = nil
      nbr_processing = nil
      nbr_processed = nil
      with_progress_bar(nbr_total, name: progress) do |progress_bar|
        loop do
          pools_semaphore.synchronize do
            nbr_to_process = pools[:to_process].size
            nbr_processing = pools[:processing].size
            nbr_processed = pools[:processed].size
          end
          progress_bar.title = "Queue: #{nbr_to_process} - Processing: #{nbr_processing} - Done: #{nbr_processed} - Total: #{nbr_total}"
          progress_bar.progress = nbr_processed
          break if nbr_processed == nbr_total
          sleep 0.5
        end
      end
    end
    # Wait for threads to be joined
    threads_to_join.each do |thread|
      thread.join
    end
  else
    # Execute synchronously
    list.each do |element|
      yield element
    end
  end
end