Clasp

Named reentrant locks with deadlock detection for Ruby

Installation & usage

Install using gem install clasp or add it to your Gemfile.

Basic usage

manager = Clasp::LockManager.new

manager.lock 'id1'
manager.unlock 'id1'

Deadlock detection

## Thread 1                                ## Thread 2
manager.lock 'AAA'                         manager.lock 'BBB'
begin                                      begin
  manager.lock 'BBB'                         manager.lock 'AAA'
  # do work...                               # do work...
  manager.unlock 'BBB'                       manager.unlock 'AAA'
ensure                                     ensure
  manager.unlock 'AAA'                       manager.unlock 'BBB'
end                                        end

Using standard locks, this program could run forever because of a deadlock. Using LockManager prevents this by tracking all locks and checking if a deadlock is about to occur.

The first thread that detects the deadlock can release any locks it holds. After this happens, it can rollback and try again later. The competing thread will then be able to lock any resources it needs to continue.

Debugging deadlocks

Clasp provides advanced debugging information when deadlocks occur.

Turn on debugging mode for your application:

Clasp.debug = true

Then log the messages for Clasp::DeadlockError. You could see informative details about how the deadlock occured:

Imminent deadlock detected

#<Thread:0x62f0 id=6 run> wanted #<DisposableLock 25296/f2057ff3-1a65-4815-ac59-91d0d73f2c87>
#<Thread:0x62e4 id=7 sleep> is waiting on a lock owned by #<Thread:0x62f0 id=6 run>

Locks owned by #<Thread:0x62f0 id=6 run>
    #<DisposableLock 25296/a8f0d33e-74db-45cd-867d-aa0ef82dfcf9>

Locks owned by #<Thread:0x62e4 id=7 sleep>
    #<DisposableLock 25296/f2057ff3-1a65-4815-ac59-91d0d73f2c87>