Class: Gitlab::ExclusiveLease
- Inherits:
-
Object
- Object
- Gitlab::ExclusiveLease
- Defined in:
- lib/gitlab/exclusive_lease.rb
Overview
This class implements an 'exclusive lease'. We call it a 'lease' because it has a set expiry time. We call it 'exclusive' because only one caller may obtain a lease for a given key at a time. The implementation is intended to work across GitLab processes and across servers. It is a cheap alternative to using SQL queries and updates: you do not need to change the SQL schema to start using ExclusiveLease.
Constant Summary collapse
- PREFIX =
'gitlab:exclusive_lease'
- NoKey =
Class.new(ArgumentError)
- LUA_CANCEL_SCRIPT =
<<~EOS.freeze local key, uuid = KEYS[1], ARGV[1] if redis.call("get", key) == uuid then redis.call("del", key) end EOS
- LUA_RENEW_SCRIPT =
<<~EOS.freeze local key, uuid, ttl = KEYS[1], ARGV[1], ARGV[2] if redis.call("get", key) == uuid then redis.call("expire", key, ttl) return uuid end EOS
Class Method Summary collapse
- .cancel(key, uuid) ⇒ Object
- .ensure_prefixed_key(key) ⇒ Object
- .get_uuid(key) ⇒ Object
- .redis_shared_state_key(key) ⇒ Object
-
.reset_all!(scope = '*') ⇒ Object
Removes any existing exclusive_lease from redis Don't run this in a live system without making sure no one is using the leases.
Instance Method Summary collapse
-
#cancel ⇒ Object
Gives up this lease, allowing it to be obtained by others.
-
#exists? ⇒ Boolean
Returns true if the key for this lease is set.
-
#initialize(key, uuid: nil, timeout:) ⇒ ExclusiveLease
constructor
A new instance of ExclusiveLease.
-
#renew ⇒ Object
Try to renew an existing lease.
-
#try_obtain ⇒ Object
Try to obtain the lease.
-
#ttl ⇒ Object
Returns the TTL of the Redis key.
Constructor Details
#initialize(key, uuid: nil, timeout:) ⇒ ExclusiveLease
Returns a new instance of ExclusiveLease.
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# File 'lib/gitlab/exclusive_lease.rb', line 67 def initialize(key, uuid: nil, timeout:) @redis_shared_state_key = self.class.redis_shared_state_key(key) @timeout = timeout @uuid = uuid || SecureRandom.uuid end |
Class Method Details
.cancel(key, uuid) ⇒ Object
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# File 'lib/gitlab/exclusive_lease.rb', line 39 def self.cancel(key, uuid) return unless key.present? Gitlab::Redis::SharedState.with do |redis| redis.eval(LUA_CANCEL_SCRIPT, keys: [ensure_prefixed_key(key)], argv: [uuid]) end end |
.ensure_prefixed_key(key) ⇒ Object
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# File 'lib/gitlab/exclusive_lease.rb', line 51 def self.ensure_prefixed_key(key) raise NoKey unless key.present? key.start_with?(PREFIX) ? key : redis_shared_state_key(key) end |
.get_uuid(key) ⇒ Object
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# File 'lib/gitlab/exclusive_lease.rb', line 33 def self.get_uuid(key) Gitlab::Redis::SharedState.with do |redis| redis.get(redis_shared_state_key(key)) || false end end |
.redis_shared_state_key(key) ⇒ Object
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# File 'lib/gitlab/exclusive_lease.rb', line 47 def self.redis_shared_state_key(key) "#{PREFIX}:#{key}" end |
.reset_all!(scope = '*') ⇒ Object
Removes any existing exclusive_lease from redis Don't run this in a live system without making sure no one is using the leases
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# File 'lib/gitlab/exclusive_lease.rb', line 59 def self.reset_all!(scope = '*') Gitlab::Redis::SharedState.with do |redis| redis.scan_each(match: redis_shared_state_key(scope)).each do |key| redis.del(key) end end end |
Instance Method Details
#cancel ⇒ Object
Gives up this lease, allowing it to be obtained by others.
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# File 'lib/gitlab/exclusive_lease.rb', line 110 def cancel self.class.cancel(@redis_shared_state_key, @uuid) end |
#exists? ⇒ Boolean
Returns true if the key for this lease is set.
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# File 'lib/gitlab/exclusive_lease.rb', line 92 def exists? Gitlab::Redis::SharedState.with do |redis| redis.exists(@redis_shared_state_key) end end |
#renew ⇒ Object
Try to renew an existing lease. Return lease UUID on success, false if the lease is taken by a different UUID or inexistent.
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# File 'lib/gitlab/exclusive_lease.rb', line 84 def renew Gitlab::Redis::SharedState.with do |redis| result = redis.eval(LUA_RENEW_SCRIPT, keys: [@redis_shared_state_key], argv: [@uuid, @timeout]) result == @uuid end end |
#try_obtain ⇒ Object
Try to obtain the lease. Return lease UUID on success, false if the lease is already taken.
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# File 'lib/gitlab/exclusive_lease.rb', line 75 def try_obtain # Performing a single SET is atomic Gitlab::Redis::SharedState.with do |redis| redis.set(@redis_shared_state_key, @uuid, nx: true, ex: @timeout) && @uuid end end |
#ttl ⇒ Object
Returns the TTL of the Redis key.
This method will return `nil` if no TTL could be obtained.
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# File 'lib/gitlab/exclusive_lease.rb', line 101 def ttl Gitlab::Redis::SharedState.with do |redis| ttl = redis.ttl(@redis_shared_state_key) ttl if ttl > 0 end end |