Class: Aeternitas::Guard

Inherits:
Object
  • Object
show all
Defined in:
lib/aeternitas/guard.rb

Overview

A distributed lock that can not be acquired after being unlocked for a certain time (cooldown period). Using Redis key expiration we ensure locks are released even after workers crash after a configurable timout period.

Examples:

guard = Aeternitas::Guard.new("Twitter-MY_API_KEY", 5.seconds)
begin
  guard.with_lock do
    twitter_client.user_timeline('Darth_Max')
  end
rescue Twitter::TooManyRequests => e
  guard.sleep_until(e.rate_limit.reset_at)
  raise Aeternitas::Guard::GuardIsLocked(e.rate_limit.reset_at)
end

Defined Under Namespace

Classes: GuardIsLocked

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(id, cooldown, timeout = 10.minutes) ⇒ Aeternitas::Guard

Create a new Guard

Parameters:

  • id (String) —

    Lock id

  • cooldown (ActiveRecord::Duration) —

    Cooldown time

  • timeout (ActiveRecord::Duration) (defaults to: 10.minutes) —

    Lock timeout



37
38
39
40
41
42
 
# File 'lib/aeternitas/guard.rb', line 37

def initialize(id, cooldown, timeout = 10.minutes)
  @id       = id
  @cooldown = cooldown
  @timeout  = timeout
  @token    = SecureRandom.hex(10)
end

Instance Attribute Details

#cooldown ⇒ ActiveSupport::Duration (readonly)

Returns cooldown time, in which the lock can’t be acquired after being released.

Returns:

  • (ActiveSupport::Duration) —

    cooldown time, in which the lock can’t be acquired after being released



27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
 
# File 'lib/aeternitas/guard.rb', line 27

class Guard

  attr_reader :id, :timeout, :cooldown, :token

  # Create a new Guard
  #
  # @param [String] id Lock id
  # @param [ActiveRecord::Duration] cooldown Cooldown time
  # @param [ActiveRecord::Duration] timeout Lock timeout
  # @return [Aeternitas::Guard] Creates a new Instance
  def initialize(id, cooldown, timeout = 10.minutes)
    @id       = id
    @cooldown = cooldown
    @timeout  = timeout
    @token    = SecureRandom.hex(10)
  end

  # Runs a given block if the lock can be acquired and releases the lock afterwards.
  #
  # @raise [Aeternitas::LockWithCooldown::GuardIsLocked] if the lock can not be acquired
  # @example
  #   Guard.new("MyId", 5.seconds, 10.minutes).with_lock { do_request() }
  def with_lock
    acquire_lock!
    begin
      yield
    ensure
      unlock
    end
  end

  # Locks the guard until the given time.
  #
  # @param [Time] until_time sleep time
  # @param [String] msg hint why the guard sleeps
  def sleep_until(until_time, msg = nil)
    sleep(until_time, msg)
  end

  # Locks the guard for the given duration.
  #
  # @param [ActiveSupport::Duration] duration sleeping duration
  # @param [String] msg hint why the guard sleeps
  def sleep_for(duration, msg = nil)
    raise ArgumentError, 'duration must be an ActiveRecord::Duration' unless duration.is_a?(ActiveSupport::Duration)
    sleep_until(duration.from_now, msg)
  end

  private

  # Tries to acquire the lock.
  #
  # @example The Redis value looks like this
  #   {
  #     id: 'MyId'
  #     state: 'processing'
  #     timeout: '3600'
  #     cooldown: '5'
  #     locked_until: '2017-01-01 10:10:00'
  #     token: '1234567890'
  #   }
  # @raise [Aeternitas::Guard::GuardIsLocked] if the lock can not be acquired
  def acquire_lock!
    payload = {
      'id' => @id,
      'state' => 'processing',
      'timeout' => @timeout,
      'cooldown' => @cooldown,
      'locked_until' => @timeout.from_now,
      'token' => @token
    }

    has_lock = Aeternitas.redis.set(@id, JSON.unparse(payload), ex: @timeout.to_i, nx: true)

    raise(GuardIsLocked.new(@id, get_timeout)) unless has_lock
  end

  # Tries to unlock the guard. This starts the cooldown phase.
  #
  # @example The Redis value looks like this
  #   {
  #     id: 'MyId'
  #     state: 'cooldown'
  #     timeout: '3600'
  #     cooldown: '5'
  #     locked_until: '2017-01-01 10:00:05'
  #     token: '1234567890'
  #   }
  def unlock
    return false unless holds_lock?

    payload = {
        'id' => @id,
        'state' => 'cooldown',
        'timeout' => @timeout,
        'cooldown' => @cooldown,
        'locked_until' => @cooldown.from_now,
        'token' => @token
    }

    Aeternitas.redis.set(@id, JSON.unparse(payload), ex: @cooldown.to_i)
  end

  # Lets the guard sleep until the given date.
  # This means that non can acquire the guards lock
  #
  # @example The Redis value looks like this
  #   {
  #     id: 'MyId'
  #     state: 'sleeping'
  #     timeout: '3600'
  #     cooldown: '5'
  #     locked_until: '2017-01-01 13:00'
  #     message: "API Quota Reached"
  #   }
  # @todo Should this raise an error if the lock is not owned by this instance?
  # @param [Time] sleep_timeout for how long will the guard sleep
  # @param [String] msg hint why the guard sleeps
  def sleep(sleep_timeout, msg = nil)
    payload = {
        'id' => @id,
        'state' => 'sleeping',
        'timeout' => @timeout,
        'cooldown' => @cooldown,
        'locked_until' => sleep_timeout
    }
    payload.merge(message: msg) if msg

    Aeternitas.redis.set(@id, JSON.unparse(payload), ex: (sleep_timeout - Time.now).seconds.to_i)
  end

  # Checks if this instance holds the lock. This is done by retrieving the value from redis and
  # comparing the token value. If they match, than the lock is held by this instance.
  #
  # @todo Make the check atomic
  # @return [Boolean] if the lock is held by this instance
  def holds_lock?
    payload = get_payload
    payload['token'] == @token && payload['state'] == 'processing'
  end

  # Returns the guards current timeout.
  #
  # @return [Time] the guards current timeout
  def get_timeout
    payload = get_payload
    payload['state'] == 'processing' ? payload['cooldown'].to_i.seconds.from_now : Time.parse(payload['locked_until'])
  end

  # Retrieves the locks payload from redis.
  #
  # @return [Hash] the locks payload
  def get_payload
    value = Aeternitas.redis.get(@id)
    return {} unless value
    JSON.parse(value)
  end

  # Custom error class thrown when the lock can not be acquired
  # @!attribute [r] timeout
  #   @return [DateTime] the locks current timeout
  class GuardIsLocked < StandardError
    attr_reader :timeout

    def initialize(resource_id, timeout, reason = nil)
      msg = "Resource '#{resource_id}' is locked until #{timeout}."
      msg += " Reason: #{reason}" if reason
      super(msg)
      @timeout = timeout
    end
  end
end

#id ⇒ String (readonly)

Returns the guards id.

Returns:

  • (String) —

    the guards id



27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
 
# File 'lib/aeternitas/guard.rb', line 27

class Guard

  attr_reader :id, :timeout, :cooldown, :token

  # Create a new Guard
  #
  # @param [String] id Lock id
  # @param [ActiveRecord::Duration] cooldown Cooldown time
  # @param [ActiveRecord::Duration] timeout Lock timeout
  # @return [Aeternitas::Guard] Creates a new Instance
  def initialize(id, cooldown, timeout = 10.minutes)
    @id       = id
    @cooldown = cooldown
    @timeout  = timeout
    @token    = SecureRandom.hex(10)
  end

  # Runs a given block if the lock can be acquired and releases the lock afterwards.
  #
  # @raise [Aeternitas::LockWithCooldown::GuardIsLocked] if the lock can not be acquired
  # @example
  #   Guard.new("MyId", 5.seconds, 10.minutes).with_lock { do_request() }
  def with_lock
    acquire_lock!
    begin
      yield
    ensure
      unlock
    end
  end

  # Locks the guard until the given time.
  #
  # @param [Time] until_time sleep time
  # @param [String] msg hint why the guard sleeps
  def sleep_until(until_time, msg = nil)
    sleep(until_time, msg)
  end

  # Locks the guard for the given duration.
  #
  # @param [ActiveSupport::Duration] duration sleeping duration
  # @param [String] msg hint why the guard sleeps
  def sleep_for(duration, msg = nil)
    raise ArgumentError, 'duration must be an ActiveRecord::Duration' unless duration.is_a?(ActiveSupport::Duration)
    sleep_until(duration.from_now, msg)
  end

  private

  # Tries to acquire the lock.
  #
  # @example The Redis value looks like this
  #   {
  #     id: 'MyId'
  #     state: 'processing'
  #     timeout: '3600'
  #     cooldown: '5'
  #     locked_until: '2017-01-01 10:10:00'
  #     token: '1234567890'
  #   }
  # @raise [Aeternitas::Guard::GuardIsLocked] if the lock can not be acquired
  def acquire_lock!
    payload = {
      'id' => @id,
      'state' => 'processing',
      'timeout' => @timeout,
      'cooldown' => @cooldown,
      'locked_until' => @timeout.from_now,
      'token' => @token
    }

    has_lock = Aeternitas.redis.set(@id, JSON.unparse(payload), ex: @timeout.to_i, nx: true)

    raise(GuardIsLocked.new(@id, get_timeout)) unless has_lock
  end

  # Tries to unlock the guard. This starts the cooldown phase.
  #
  # @example The Redis value looks like this
  #   {
  #     id: 'MyId'
  #     state: 'cooldown'
  #     timeout: '3600'
  #     cooldown: '5'
  #     locked_until: '2017-01-01 10:00:05'
  #     token: '1234567890'
  #   }
  def unlock
    return false unless holds_lock?

    payload = {
        'id' => @id,
        'state' => 'cooldown',
        'timeout' => @timeout,
        'cooldown' => @cooldown,
        'locked_until' => @cooldown.from_now,
        'token' => @token
    }

    Aeternitas.redis.set(@id, JSON.unparse(payload), ex: @cooldown.to_i)
  end

  # Lets the guard sleep until the given date.
  # This means that non can acquire the guards lock
  #
  # @example The Redis value looks like this
  #   {
  #     id: 'MyId'
  #     state: 'sleeping'
  #     timeout: '3600'
  #     cooldown: '5'
  #     locked_until: '2017-01-01 13:00'
  #     message: "API Quota Reached"
  #   }
  # @todo Should this raise an error if the lock is not owned by this instance?
  # @param [Time] sleep_timeout for how long will the guard sleep
  # @param [String] msg hint why the guard sleeps
  def sleep(sleep_timeout, msg = nil)
    payload = {
        'id' => @id,
        'state' => 'sleeping',
        'timeout' => @timeout,
        'cooldown' => @cooldown,
        'locked_until' => sleep_timeout
    }
    payload.merge(message: msg) if msg

    Aeternitas.redis.set(@id, JSON.unparse(payload), ex: (sleep_timeout - Time.now).seconds.to_i)
  end

  # Checks if this instance holds the lock. This is done by retrieving the value from redis and
  # comparing the token value. If they match, than the lock is held by this instance.
  #
  # @todo Make the check atomic
  # @return [Boolean] if the lock is held by this instance
  def holds_lock?
    payload = get_payload
    payload['token'] == @token && payload['state'] == 'processing'
  end

  # Returns the guards current timeout.
  #
  # @return [Time] the guards current timeout
  def get_timeout
    payload = get_payload
    payload['state'] == 'processing' ? payload['cooldown'].to_i.seconds.from_now : Time.parse(payload['locked_until'])
  end

  # Retrieves the locks payload from redis.
  #
  # @return [Hash] the locks payload
  def get_payload
    value = Aeternitas.redis.get(@id)
    return {} unless value
    JSON.parse(value)
  end

  # Custom error class thrown when the lock can not be acquired
  # @!attribute [r] timeout
  #   @return [DateTime] the locks current timeout
  class GuardIsLocked < StandardError
    attr_reader :timeout

    def initialize(resource_id, timeout, reason = nil)
      msg = "Resource '#{resource_id}' is locked until #{timeout}."
      msg += " Reason: #{reason}" if reason
      super(msg)
      @timeout = timeout
    end
  end
end

#timeout ⇒ ActiveSupport::Duration (readonly)

Returns the locks timeout duration.

Returns:

  • (ActiveSupport::Duration) —

    the locks timeout duration



27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
 
# File 'lib/aeternitas/guard.rb', line 27

class Guard

  attr_reader :id, :timeout, :cooldown, :token

  # Create a new Guard
  #
  # @param [String] id Lock id
  # @param [ActiveRecord::Duration] cooldown Cooldown time
  # @param [ActiveRecord::Duration] timeout Lock timeout
  # @return [Aeternitas::Guard] Creates a new Instance
  def initialize(id, cooldown, timeout = 10.minutes)
    @id       = id
    @cooldown = cooldown
    @timeout  = timeout
    @token    = SecureRandom.hex(10)
  end

  # Runs a given block if the lock can be acquired and releases the lock afterwards.
  #
  # @raise [Aeternitas::LockWithCooldown::GuardIsLocked] if the lock can not be acquired
  # @example
  #   Guard.new("MyId", 5.seconds, 10.minutes).with_lock { do_request() }
  def with_lock
    acquire_lock!
    begin
      yield
    ensure
      unlock
    end
  end

  # Locks the guard until the given time.
  #
  # @param [Time] until_time sleep time
  # @param [String] msg hint why the guard sleeps
  def sleep_until(until_time, msg = nil)
    sleep(until_time, msg)
  end

  # Locks the guard for the given duration.
  #
  # @param [ActiveSupport::Duration] duration sleeping duration
  # @param [String] msg hint why the guard sleeps
  def sleep_for(duration, msg = nil)
    raise ArgumentError, 'duration must be an ActiveRecord::Duration' unless duration.is_a?(ActiveSupport::Duration)
    sleep_until(duration.from_now, msg)
  end

  private

  # Tries to acquire the lock.
  #
  # @example The Redis value looks like this
  #   {
  #     id: 'MyId'
  #     state: 'processing'
  #     timeout: '3600'
  #     cooldown: '5'
  #     locked_until: '2017-01-01 10:10:00'
  #     token: '1234567890'
  #   }
  # @raise [Aeternitas::Guard::GuardIsLocked] if the lock can not be acquired
  def acquire_lock!
    payload = {
      'id' => @id,
      'state' => 'processing',
      'timeout' => @timeout,
      'cooldown' => @cooldown,
      'locked_until' => @timeout.from_now,
      'token' => @token
    }

    has_lock = Aeternitas.redis.set(@id, JSON.unparse(payload), ex: @timeout.to_i, nx: true)

    raise(GuardIsLocked.new(@id, get_timeout)) unless has_lock
  end

  # Tries to unlock the guard. This starts the cooldown phase.
  #
  # @example The Redis value looks like this
  #   {
  #     id: 'MyId'
  #     state: 'cooldown'
  #     timeout: '3600'
  #     cooldown: '5'
  #     locked_until: '2017-01-01 10:00:05'
  #     token: '1234567890'
  #   }
  def unlock
    return false unless holds_lock?

    payload = {
        'id' => @id,
        'state' => 'cooldown',
        'timeout' => @timeout,
        'cooldown' => @cooldown,
        'locked_until' => @cooldown.from_now,
        'token' => @token
    }

    Aeternitas.redis.set(@id, JSON.unparse(payload), ex: @cooldown.to_i)
  end

  # Lets the guard sleep until the given date.
  # This means that non can acquire the guards lock
  #
  # @example The Redis value looks like this
  #   {
  #     id: 'MyId'
  #     state: 'sleeping'
  #     timeout: '3600'
  #     cooldown: '5'
  #     locked_until: '2017-01-01 13:00'
  #     message: "API Quota Reached"
  #   }
  # @todo Should this raise an error if the lock is not owned by this instance?
  # @param [Time] sleep_timeout for how long will the guard sleep
  # @param [String] msg hint why the guard sleeps
  def sleep(sleep_timeout, msg = nil)
    payload = {
        'id' => @id,
        'state' => 'sleeping',
        'timeout' => @timeout,
        'cooldown' => @cooldown,
        'locked_until' => sleep_timeout
    }
    payload.merge(message: msg) if msg

    Aeternitas.redis.set(@id, JSON.unparse(payload), ex: (sleep_timeout - Time.now).seconds.to_i)
  end

  # Checks if this instance holds the lock. This is done by retrieving the value from redis and
  # comparing the token value. If they match, than the lock is held by this instance.
  #
  # @todo Make the check atomic
  # @return [Boolean] if the lock is held by this instance
  def holds_lock?
    payload = get_payload
    payload['token'] == @token && payload['state'] == 'processing'
  end

  # Returns the guards current timeout.
  #
  # @return [Time] the guards current timeout
  def get_timeout
    payload = get_payload
    payload['state'] == 'processing' ? payload['cooldown'].to_i.seconds.from_now : Time.parse(payload['locked_until'])
  end

  # Retrieves the locks payload from redis.
  #
  # @return [Hash] the locks payload
  def get_payload
    value = Aeternitas.redis.get(@id)
    return {} unless value
    JSON.parse(value)
  end

  # Custom error class thrown when the lock can not be acquired
  # @!attribute [r] timeout
  #   @return [DateTime] the locks current timeout
  class GuardIsLocked < StandardError
    attr_reader :timeout

    def initialize(resource_id, timeout, reason = nil)
      msg = "Resource '#{resource_id}' is locked until #{timeout}."
      msg += " Reason: #{reason}" if reason
      super(msg)
      @timeout = timeout
    end
  end
end

#token ⇒ String (readonly)

Returns cryptographic token which ensures we do not lock/unlock a guard held by another process.

Returns:

  • (String) —

    cryptographic token which ensures we do not lock/unlock a guard held by another process



27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
 
# File 'lib/aeternitas/guard.rb', line 27

class Guard

  attr_reader :id, :timeout, :cooldown, :token

  # Create a new Guard
  #
  # @param [String] id Lock id
  # @param [ActiveRecord::Duration] cooldown Cooldown time
  # @param [ActiveRecord::Duration] timeout Lock timeout
  # @return [Aeternitas::Guard] Creates a new Instance
  def initialize(id, cooldown, timeout = 10.minutes)
    @id       = id
    @cooldown = cooldown
    @timeout  = timeout
    @token    = SecureRandom.hex(10)
  end

  # Runs a given block if the lock can be acquired and releases the lock afterwards.
  #
  # @raise [Aeternitas::LockWithCooldown::GuardIsLocked] if the lock can not be acquired
  # @example
  #   Guard.new("MyId", 5.seconds, 10.minutes).with_lock { do_request() }
  def with_lock
    acquire_lock!
    begin
      yield
    ensure
      unlock
    end
  end

  # Locks the guard until the given time.
  #
  # @param [Time] until_time sleep time
  # @param [String] msg hint why the guard sleeps
  def sleep_until(until_time, msg = nil)
    sleep(until_time, msg)
  end

  # Locks the guard for the given duration.
  #
  # @param [ActiveSupport::Duration] duration sleeping duration
  # @param [String] msg hint why the guard sleeps
  def sleep_for(duration, msg = nil)
    raise ArgumentError, 'duration must be an ActiveRecord::Duration' unless duration.is_a?(ActiveSupport::Duration)
    sleep_until(duration.from_now, msg)
  end

  private

  # Tries to acquire the lock.
  #
  # @example The Redis value looks like this
  #   {
  #     id: 'MyId'
  #     state: 'processing'
  #     timeout: '3600'
  #     cooldown: '5'
  #     locked_until: '2017-01-01 10:10:00'
  #     token: '1234567890'
  #   }
  # @raise [Aeternitas::Guard::GuardIsLocked] if the lock can not be acquired
  def acquire_lock!
    payload = {
      'id' => @id,
      'state' => 'processing',
      'timeout' => @timeout,
      'cooldown' => @cooldown,
      'locked_until' => @timeout.from_now,
      'token' => @token
    }

    has_lock = Aeternitas.redis.set(@id, JSON.unparse(payload), ex: @timeout.to_i, nx: true)

    raise(GuardIsLocked.new(@id, get_timeout)) unless has_lock
  end

  # Tries to unlock the guard. This starts the cooldown phase.
  #
  # @example The Redis value looks like this
  #   {
  #     id: 'MyId'
  #     state: 'cooldown'
  #     timeout: '3600'
  #     cooldown: '5'
  #     locked_until: '2017-01-01 10:00:05'
  #     token: '1234567890'
  #   }
  def unlock
    return false unless holds_lock?

    payload = {
        'id' => @id,
        'state' => 'cooldown',
        'timeout' => @timeout,
        'cooldown' => @cooldown,
        'locked_until' => @cooldown.from_now,
        'token' => @token
    }

    Aeternitas.redis.set(@id, JSON.unparse(payload), ex: @cooldown.to_i)
  end

  # Lets the guard sleep until the given date.
  # This means that non can acquire the guards lock
  #
  # @example The Redis value looks like this
  #   {
  #     id: 'MyId'
  #     state: 'sleeping'
  #     timeout: '3600'
  #     cooldown: '5'
  #     locked_until: '2017-01-01 13:00'
  #     message: "API Quota Reached"
  #   }
  # @todo Should this raise an error if the lock is not owned by this instance?
  # @param [Time] sleep_timeout for how long will the guard sleep
  # @param [String] msg hint why the guard sleeps
  def sleep(sleep_timeout, msg = nil)
    payload = {
        'id' => @id,
        'state' => 'sleeping',
        'timeout' => @timeout,
        'cooldown' => @cooldown,
        'locked_until' => sleep_timeout
    }
    payload.merge(message: msg) if msg

    Aeternitas.redis.set(@id, JSON.unparse(payload), ex: (sleep_timeout - Time.now).seconds.to_i)
  end

  # Checks if this instance holds the lock. This is done by retrieving the value from redis and
  # comparing the token value. If they match, than the lock is held by this instance.
  #
  # @todo Make the check atomic
  # @return [Boolean] if the lock is held by this instance
  def holds_lock?
    payload = get_payload
    payload['token'] == @token && payload['state'] == 'processing'
  end

  # Returns the guards current timeout.
  #
  # @return [Time] the guards current timeout
  def get_timeout
    payload = get_payload
    payload['state'] == 'processing' ? payload['cooldown'].to_i.seconds.from_now : Time.parse(payload['locked_until'])
  end

  # Retrieves the locks payload from redis.
  #
  # @return [Hash] the locks payload
  def get_payload
    value = Aeternitas.redis.get(@id)
    return {} unless value
    JSON.parse(value)
  end

  # Custom error class thrown when the lock can not be acquired
  # @!attribute [r] timeout
  #   @return [DateTime] the locks current timeout
  class GuardIsLocked < StandardError
    attr_reader :timeout

    def initialize(resource_id, timeout, reason = nil)
      msg = "Resource '#{resource_id}' is locked until #{timeout}."
      msg += " Reason: #{reason}" if reason
      super(msg)
      @timeout = timeout
    end
  end
end

Instance Method Details

#sleep_for(duration, msg = nil) ⇒ Object

Locks the guard for the given duration.

Parameters:

  • duration (ActiveSupport::Duration) —

    sleeping duration

  • msg (String) (defaults to: nil) —

    hint why the guard sleeps

Raises:

  • (ArgumentError) 


70
71
72
73
 
# File 'lib/aeternitas/guard.rb', line 70

def sleep_for(duration, msg = nil)
  raise ArgumentError, 'duration must be an ActiveRecord::Duration' unless duration.is_a?(ActiveSupport::Duration)
  sleep_until(duration.from_now, msg)
end

#sleep_until(until_time, msg = nil) ⇒ Object

Locks the guard until the given time.

Parameters:

  • until_time (Time) —

    sleep time

  • msg (String) (defaults to: nil) —

    hint why the guard sleeps



62
63
64
 
# File 'lib/aeternitas/guard.rb', line 62

def sleep_until(until_time, msg = nil)
  sleep(until_time, msg)
end

#with_lock ⇒ Object

Runs a given block if the lock can be acquired and releases the lock afterwards.

Examples:

Guard.new("MyId", 5.seconds, 10.minutes).with_lock { do_request() }

Raises:

  • (Aeternitas::LockWithCooldown::GuardIsLocked) —

    if the lock can not be acquired



49
50
51
52
53
54
55
56
 
# File 'lib/aeternitas/guard.rb', line 49

def with_lock
  acquire_lock!
  begin
    yield
  ensure
    unlock
  end
end