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/Crystal

class Sync::Exclusive(T)

Overview

Safely share a value T across fibers and execution contexts using a Mutex, so only one critical section can access the value at any time.

For example:

require "sync/exclusive"

class Queue
  @@running : Sync::Exclusive.new([] of Queue)

  def self.on_started(queue)
    @@running.lock(&.push(queue))
  end

  def self.on_stopped(queue)
    @@running.lock(&.delete(queue))
  end

  def self.each(&)
    @@running.lock do |list|
      list.each { |queue| yield queue }
    end
  end
end

Consider an Exclusive(T) if your workload mostly needs to own the value, and most, if not all, critical sections need to mutate the inner state of the value for example.

Included Modules

Sync::Lockable

Defined in:

sync/exclusive.cr

Constructors

.new(value : T, type : Type = :checked)

Instance Method Summary

#get : T
Locks the mutex and returns the value.
#lock(& : T -> U) : U forall U
Locks the mutex and yields the value.
#replace(& : T -> T) : Nil
Locks the mutex, yields the value and eventually replaces the value with the one returned by the block.
#set(value : T) : Nil
Locks the mutex and sets the value.
#unsafe_get : T
Returns the value without any synchronization.
#unsafe_set(value : T) : T
Sets the value without any synchronization.

Instance methods inherited from class `Reference`

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Constructor methods inherited from class `Reference`

Class methods inherited from class `Reference`

Instance methods inherited from class `Object`

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Class methods inherited from class `Object`

Macros inherited from class `Object`

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Constructor Detail

def self.new(value : T, type : Type = :checked)Source

Instance Method Detail

def get : TSource

Locks the mutex and returns the value. Unlocks before returning.

Always acquires the lock, so reading the value is synchronized in relation with the other methods. However, safely accessing the returned value entirely depends on the safety of T.

Prefer #lock(&.dup) or #lock(&.clone) to get a shallow or deep copy of the value instead.

WARNING Breaks the mutual exclusion guarantee since the returned value outlives the lock, the value can be accessed concurrently to the synchronized methods.

def lock(& : T -> U) : U forall USource

Locks the mutex and yields the value. The lock is released before returning.

The value is owned for the duration of the block, and can be safely mutated.

WARNING The value musn't be retained and accessed after the block has returned.

def replace(& : T -> T) : Nil Source

Locks the mutex, yields the value and eventually replaces the value with the one returned by the block. The lock is released before returning.

The current value is now owned: it can be safely retained and mutated even after the block returned.

WARNING The new value musn't be retained and accessed after the block has returned.

def set(value : T) : Nil Source

Locks the mutex and sets the value. Unlocks the mutex before returning.

Always acquires and releases the lock, so writing the value is always synchronized with the other methods.

def unsafe_get : TSource

Returns the value without any synchronization.

WARNING Breaks the mutual exclusion constraint! Should only be called after acquiring the lock.

def unsafe_set(value : T) : TSource

Sets the value without any synchronization.