Class: Redis::Mutex

Inherits:
Classy
  • Object
show all
Defined in:
lib/redis/mutex.rb,
lib/redis/mutex/macro.rb

Overview

Options

:block => Specify in seconds how long you want to wait for the lock to be released. Speficy 0

if you need non-blocking sematics and return false immediately. (default: 1)

:sleep => Specify in seconds how long the polling interval should be when :block is given.

It is recommended that you do NOT go below 0.01. (default: 0.1)

:expire => Specify in seconds when the lock should forcibly be removed when something went wrong

with the one who held the lock. (default: 10)

Defined Under Namespace

Modules: Macro

Constant Summary collapse

DEFAULT_EXPIRE = 
10
LockError = 
Class.new(StandardError)
UnlockError = 
Class.new(StandardError)
AssertionError = 
Class.new(StandardError)

Class Method Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(object, options = {}) ⇒ Mutex

Returns a new instance of Mutex.



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# File 'lib/redis/mutex.rb', line 20

def initialize(object, options={})
  super(object.is_a?(String) || object.is_a?(Symbol) ? object : "#{object.class.name}:#{object.id}")
  @block = options[:block] || 1
  @sleep = options[:sleep] || 0.1
  @expire = options[:expire] || DEFAULT_EXPIRE
end

Class Method Details

.lock(object, options = {}) ⇒ Object 



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# File 'lib/redis/mutex.rb', line 116

def lock(object, options = {})
  raise_assertion_error if block_given?
  new(object, options).lock
end

.lock!(object, options = {}) ⇒ Object 



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# File 'lib/redis/mutex.rb', line 121

def lock!(object, options = {})
  new(object, options).lock!
end

.raise_assertion_error ⇒ Object

Raises:



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# File 'lib/redis/mutex.rb', line 129

def raise_assertion_error
  raise AssertionError, 'block syntax has been removed from #lock, use #with_lock instead'
end

.sweep ⇒ Object 



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# File 'lib/redis/mutex.rb', line 98

def sweep
  return 0 if (all_keys = keys).empty?

  now = Time.now.to_f
  values = mget(*all_keys)

  expired_keys = all_keys.zip(values).select do |key, time|
    time && time.to_f <= now
  end

  expired_keys.each do |key, _|
    # Make extra sure that anyone haven't extended the lock
    del(key) if getset(key, now + DEFAULT_EXPIRE).to_f <= now
  end

  expired_keys.size
end

.with_lock(object, options = {}, &block) ⇒ Object 



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# File 'lib/redis/mutex.rb', line 125

def with_lock(object, options = {}, &block)
  new(object, options).with_lock(&block)
end

Instance Method Details

#lock ⇒ Object 



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# File 'lib/redis/mutex.rb', line 27

def lock
  self.class.raise_assertion_error if block_given?
  @locking = false

  if @block > 0
    # Blocking mode
    start_at = Time.now
    while Time.now - start_at < @block
      @locking = true and break if try_lock
      sleep @sleep
    end
  else
    # Non-blocking mode
    @locking = try_lock
  end
  @locking
end

#lock! ⇒ Object 



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# File 'lib/redis/mutex.rb', line 89

def lock!
  lock or raise LockError, "failed to acquire lock #{key.inspect}"
end

#locked? ⇒ Boolean

Returns true if resource is locked. Note that nil.to_f returns 0.0

Returns:

  • (Boolean) 


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# File 'lib/redis/mutex.rb', line 61

def locked?
  get.to_f > Time.now.to_f
end

#try_lock ⇒ Object 



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# File 'lib/redis/mutex.rb', line 45

def try_lock
  now = Time.now.to_f
  @expires_at = now + @expire                       # Extend in each blocking loop

  loop do
    return true if setnx(@expires_at)               # Success, the lock has been acquired
  end until old_value = get                         # Repeat if unlocked before get

  return false if old_value.to_f > now              # Check if the lock is still effective

  # The lock has expired but wasn't released... BAD!
  return true if getset(@expires_at).to_f <= now    # Success, we acquired the previously expired lock
  return false # Dammit, it seems that someone else was even faster than us to remove the expired lock!
end

#unlock(force = false) ⇒ Object 



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# File 'lib/redis/mutex.rb', line 65

def unlock(force = false)
  # Since it's possible that the operations in the critical section took a long time,
  # we can't just simply release the lock. The unlock method checks if @expires_at
  # remains the same, and do not release when the lock timestamp was overwritten.

  if get == @expires_at.to_s or force
    # Redis#del with a single key returns '1' or nil
    !!del
  else
    false
  end
end

#unlock!(force = false) ⇒ Object 



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# File 'lib/redis/mutex.rb', line 93

def unlock!(force = false)
  unlock(force) or raise UnlockError, "failed to release lock #{key.inspect}"
end

#with_lock ⇒ Object 



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# File 'lib/redis/mutex.rb', line 78

def with_lock
  if lock!
    begin
      @result = yield
    ensure
      unlock
    end
  end
  @result
end