123456789_123456789_123456789_123456789_123456789_

Class: Concurrent::Semaphore

Relationships & Source Files
Inherits: Concurrent::SemaphoreImplementation
Defined in: lib/concurrent-ruby/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. Alternatively, permits may be acquired within a block, and automatically released after the block finishes executing.

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
semaphore = Concurrent::Semaphore.new(1)

puts semaphore.available_permits
semaphore.acquire do
  puts semaphore.available_permits
end
puts semaphore.available_permits

# prints:
# 1
# 0
# 1

Class Method Summary

  • .new(count) constructor

    Create a new Semaphore with the initial count.

Instance Method Summary

Constructor Details

.new(count)

Create a new Semaphore with the initial count.

Parameters:

  • count (Fixnum) —

    the initial count

Raises:

  • (ArgumentError) —

    if count is not an integer

[ GitHub ] 

  


# File 'lib/concurrent-ruby/concurrent/atomic/semaphore.rb', line 161



class Semaphore < SemaphoreImplementation
end


  







Instance Method Details



  

    #acquire(permits = 1)  ⇒ nil, BasicObject 
  



  

    

Acquires the given number of permits from this semaphore,



blocking until all are available. If a block is given,
yields to it and releases the permits afterwards.



is given, its return value is returned.


  





  
Parameters:


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

    Number of permits to acquire
    

    
  
    • 



Returns:


    
  
  • 
    (nil, BasicObject)
—    
    

    Without a block, nil is returned. If a block
    

    
  
    • 



Raises:


    
  
  • 
    (ArgumentError)
—    
    

    if permits is not an integer or is less than zero
    

    
  
    • 





  [ GitHub ]


  

  


# File 'lib/concurrent-ruby/concurrent/atomic/semaphore.rb', line 161



class Semaphore < SemaphoreImplementation
end


  








  

    #available_permits  ⇒ Integer 
  



  

    

Returns the current number of permits available in this semaphore.


  





  


  [ GitHub ]


  

  


# File 'lib/concurrent-ruby/concurrent/atomic/semaphore.rb', line 161



class Semaphore < SemaphoreImplementation
end


  








  

    #drain_permits  ⇒ Integer 
  



  

    

Acquires and returns all permits that are immediately available.


  





  


  [ GitHub ]


  

  


# File 'lib/concurrent-ruby/concurrent/atomic/semaphore.rb', line 161



class Semaphore < SemaphoreImplementation
end


  








  

    #release(permits = 1)  ⇒ nil 
  



  

    

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.
    

    
  
    • 



Raises:


    
  
  • 
    (ArgumentError)
—    
    

    if permits is not a number or is less than zero
    

    
  
    • 





  [ GitHub ]


  

  


# File 'lib/concurrent-ruby/concurrent/atomic/semaphore.rb', line 161



class Semaphore < SemaphoreImplementation
end


  








  

    #try_acquire(permits = 1, timeout = nil)  ⇒ true, ... 
  



  

    

Acquires the given number of permits from this semaphore,



only if all are available at the time of invocation or within
{timeout} interval. If a block is given, yields to it if the permits
were successfully acquired, and releases them afterward, returning the
block's return value.


  





  
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:


    
  
  • 
    (true, false, nil, BasicObject)
—    
    

    false if no permits are available, true when acquired a permit. If a block is given, the block’s return value is returned if the permits were acquired; if not, nil is returned.
    

    
  
    • 



Raises:


    
  
  • 
    (ArgumentError)
—    
    

    if permits is not an integer or is less than zero
    

    
  
    • 





  [ GitHub ]


  

  


# File 'lib/concurrent-ruby/concurrent/atomic/semaphore.rb', line 161



class Semaphore < SemaphoreImplementation
end