Class: Concurrent::Semaphore

Inherits:
SemaphoreImplementation
  • Object
show all
Defined in:
lib/concurrent/atomic/semaphore.rb

Overview

A counting semaphore. Conceptually, a semaphore maintains a set of permits. Each #acquire blocks if necessary until a permit is available, and then takes it. Each #release adds a permit, potentially releasing a blocking acquirer. However, no actual permit objects are used; the Semaphore just keeps a count of the number available and acts accordingly.

Examples:

semaphore = Concurrent::Semaphore.new(2)

t1 = Thread.new do
  semaphore.acquire
  puts "Thread 1 acquired semaphore"
end

t2 = Thread.new do
  semaphore.acquire
  puts "Thread 2 acquired semaphore"
end

t3 = Thread.new do
  semaphore.acquire
  puts "Thread 3 acquired semaphore"
end

t4 = Thread.new do
  sleep(2)
  puts "Thread 4 releasing semaphore"
  semaphore.release
end

[t1, t2, t3, t4].each(&:join)

# prints:
# Thread 3 acquired semaphore
# Thread 2 acquired semaphore
# Thread 4 releasing semaphore
# Thread 1 acquired semaphore

Instance Method Summary (collapse)

Constructor Details

- (undocumented) initialize(count)

Create a new Semaphore with the initial count.

Parameters:

  • count (Fixnum)

    the initial count

Raises:

  • (ArgumentError)

    if count is not an integer or is less than zero



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# File 'lib/concurrent/atomic/semaphore.rb', line 143

class Semaphore < SemaphoreImplementation
end

Instance Method Details

- (nil) acquire(permits = 1)

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

Parameters:

  • permits (Fixnum) (defaults to: 1)

    Number of permits to acquire

Returns:

  • (nil)

Raises:

  • (ArgumentError)

    if permits is not an integer or is less than one



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# File 'lib/concurrent/atomic/semaphore.rb', line 143

class Semaphore < SemaphoreImplementation
end

- (Integer) available_permits

Returns the current number of permits available in this semaphore.

Returns:

  • (Integer)


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# File 'lib/concurrent/atomic/semaphore.rb', line 143

class Semaphore < SemaphoreImplementation
end

- (Integer) drain_permits

Acquires and returns all permits that are immediately available.

Returns:

  • (Integer)


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# File 'lib/concurrent/atomic/semaphore.rb', line 143

class Semaphore < SemaphoreImplementation
end

- (nil) release(permits = 1)

Releases the given number of permits, returning them to the semaphore.

Parameters:

  • permits (Fixnum) (defaults to: 1)

    Number of permits to return to the semaphore.

Returns:

  • (nil)

Raises:

  • (ArgumentError)

    if permits is not a number or is less than one



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# File 'lib/concurrent/atomic/semaphore.rb', line 143

class Semaphore < SemaphoreImplementation
end

- (Boolean) try_acquire(permits = 1, timeout = nil)

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

Parameters:

  • permits (Fixnum) (defaults to: 1)

    the number of permits to acquire

  • timeout (Fixnum) (defaults to: nil)

    the number of seconds to wait for the counter or nil to return immediately

Returns:

  • (Boolean)

    false if no permits are available, true when acquired a permit

Raises:

  • (ArgumentError)

    if permits is not an integer or is less than one



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# File 'lib/concurrent/atomic/semaphore.rb', line 143

class Semaphore < SemaphoreImplementation
end