Class: CountingSemaphore::LocalSemaphore

Inherits:
Object
  • Object
show all
Includes:
WithLeaseSupport
Defined in:
lib/counting_semaphore/local_semaphore.rb

Constant Summary collapse

SLEEP_WAIT_SECONDS = 
0.25

Instance Attribute Summary collapse

Instance Method Summary collapse

Methods included from WithLeaseSupport

#currently_leased, #with_lease

Constructor Details

#initialize(capacity, logger: CountingSemaphore::NullLogger) ⇒ LocalSemaphore

Initialize the semaphore with a maximum capacity.

Parameters:

  • capacity (Integer) —

    Maximum number of concurrent operations allowed (also called permits)

  • logger (Logger) (defaults to: CountingSemaphore::NullLogger) —

    the logger

Raises:

  • (ArgumentError) —

    if capacity is not positive



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# File 'lib/counting_semaphore/local_semaphore.rb', line 20

def initialize(capacity, logger: CountingSemaphore::NullLogger)
  raise ArgumentError, "Capacity must be positive, got #{capacity}" unless capacity >= 1
  @capacity = capacity.to_i
  @acquired = 0
  @mutex = Mutex.new
  @condition = ConditionVariable.new
  @logger = logger
end

Instance Attribute Details

#capacity ⇒ Integer (readonly)

Returns:

  • (Integer) 


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# File 'lib/counting_semaphore/local_semaphore.rb', line 13

def capacity
  @capacity
end

Instance Method Details

#acquire(permits = 1) ⇒ CountingSemaphore::Lease

Acquires the given number of permits from this semaphore, blocking until all are available.

Parameters:

  • permits (Integer) (defaults to: 1) —

    Number of permits to acquire (default: 1)

Returns:

Raises:

  • (ArgumentError) —

    if permits is not an integer or is less than one



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# File 'lib/counting_semaphore/local_semaphore.rb', line 34

def acquire(permits = 1)
  permits = permits.to_i
  raise ArgumentError, "Permits must be at least 1, got #{permits}" if permits < 1
  if permits > @capacity
    raise ArgumentError, "Cannot acquire #{permits} permits as capacity is only #{@capacity}"
  end

  loop do
    acquired = @mutex.synchronize do
      if (@capacity - @acquired) >= permits
        @acquired += permits
        @logger.debug { "Acquired #{permits} permits, now #{@acquired}/#{@capacity}" }
        true
      else
        false
      end
    end

    if acquired
      lease_id = "local_#{object_id}_#{Time.now.to_f}_#{rand(1000000)}"
      return CountingSemaphore::Lease.new(
        semaphore: self,
        id: lease_id,
        permits: permits
      )
    end

    @logger.debug { "Unable to acquire #{permits} permits, #{@acquired}/#{@capacity} in use, waiting" }
    @mutex.synchronize do
      @condition.wait(@mutex)
    end
  end
end

#available_permits ⇒ Integer

Returns the current number of permits available in this semaphore.

Returns:

  • (Integer) —

    Number of available permits



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# File 'lib/counting_semaphore/local_semaphore.rb', line 146

def available_permits
  @mutex.synchronize { @capacity - @acquired }
end

#drain_permits ⇒ CountingSemaphore::Lease?

Acquires and returns all permits that are immediately available. Returns a single lease representing all drained permits.

Returns:



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# File 'lib/counting_semaphore/local_semaphore.rb', line 154

def drain_permits
  permits = @mutex.synchronize do
    available = @capacity - @acquired
    if available > 0
      @acquired = @capacity
      @logger.debug { "Drained #{available} permits" }
      available
    else
      0
    end
  end

  if permits > 0
    lease_id = "local_#{object_id}_#{Time.now.to_f}_#{rand(1000000)}"
    CountingSemaphore::Lease.new(
      semaphore: self,
      id: lease_id,
      permits: permits
    )
  end
end

#release(lease) ⇒ nil

Releases a previously acquired lease, returning the permits to the semaphore.

Parameters:

Returns:

  • (nil)

Raises:

  • (ArgumentError) —

    if lease belongs to a different semaphore



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# File 'lib/counting_semaphore/local_semaphore.rb', line 73

def release(lease)
  unless lease.semaphore == self
    raise ArgumentError, "Lease belongs to a different semaphore"
  end

  permits = lease.permits

  @mutex.synchronize do
    @acquired -= permits
    @logger.debug { "Released #{permits} permits (lease: #{lease.id}), now #{@acquired}/#{@capacity}" }
    @condition.broadcast # Signal waiting threads
  end
  nil
end

#try_acquire(permits = 1, timeout: nil) ⇒ CountingSemaphore::Lease?

Acquires the given number of permits from this semaphore, only if all are available at the time of invocation or within the timeout interval.

Parameters:

  • permits (Integer) (defaults to: 1) —

    Number of permits to acquire (default: 1)

  • timeout (Numeric, nil) (defaults to: nil) —

    Number of seconds to wait, or nil to return immediately (default: nil)

Returns:

Raises:

  • (ArgumentError) —

    if permits is not an integer or is less than one



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# File 'lib/counting_semaphore/local_semaphore.rb', line 95

def try_acquire(permits = 1, timeout: nil)
  permits = permits.to_i
  raise ArgumentError, "Permits must be at least 1, got #{permits}" if permits < 1
  if permits > @capacity
    return nil
  end

  start_time = Process.clock_gettime(Process::CLOCK_MONOTONIC) if timeout

  loop do
    # Check timeout
    if timeout
      elapsed_time = Process.clock_gettime(Process::CLOCK_MONOTONIC) - start_time
      return nil if elapsed_time >= timeout
    end

    acquired = @mutex.synchronize do
      if (@capacity - @acquired) >= permits
        @acquired += permits
        @logger.debug { "Acquired #{permits} permits (try), now #{@acquired}/#{@capacity}" }
        true
      else
        false
      end
    end

    if acquired
      lease_id = "local_#{object_id}_#{Time.now.to_f}_#{rand(1000000)}"
      return CountingSemaphore::Lease.new(
        semaphore: self,
        id: lease_id,
        permits: permits
      )
    end

    # If no timeout, return immediately
    return nil if timeout.nil?

    # Wait with remaining timeout
    remaining_timeout = timeout - (Process.clock_gettime(Process::CLOCK_MONOTONIC) - start_time)
    return nil if remaining_timeout <= 0

    @mutex.synchronize do
      @condition.wait(@mutex, remaining_timeout)
    end
  end
end