Rename ExpiringLock to ExclusiveLease

1 files changed, 37 insertions, 0 deletions

diff --git a/lib/gitlab/exclusive_lease.rb b/lib/gitlab/exclusive_lease.rb
new file mode 100644
index 00000000000..f801e8b60b3
--- /dev/null
+++ b/lib/gitlab/exclusive_lease.rb
@@ -0,0 +1,37 @@
+require 'securerandom'
+
+module Gitlab
+  # 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.
+  class ExclusiveLease
+    def initialize(key, timeout)
+      @key, @timeout = key, timeout
+    end
+
+    # Try to obtain the lease. Return true on succes,
+    # false if the lease is already taken.
+    def try_obtain
+      !!redis.set(redis_key, redis_value, nx: true, ex: @timeout)
+    end
+
+    private
+
+    def redis
+      # Maybe someday we want to use a connection pool...
+      @redis ||= Redis.new(url: Gitlab::RedisConfig.url)
+    end
+
+    def redis_key
+      "gitlab:exclusive_lease:#{@key}"
+    end
+
+    def redis_value
+      @redis_value ||= SecureRandom.hex(10)
+    end
+  end
+end