Class: Spinoza::LockManager

Inherits:
Object
  • Object
show all
Defined in:
lib/spinoza/system/lock-manager.rb

Overview

Manages concurrency in the spinoza system model, which explicitly schedules all database reads and writes. So all this does is check for concurrency violations; nothing actually blocks.

The txn references in this class care only about identity, so they could all be ids or they could all be transaction objects. Similarly the resource being locked by a ReadLock or WriteLock can be anything whose identity is defined by hash equality, i.e. #eql?. Typically, we use ‘[table, key]` pairs, where `key` is a primary key reference like `…`.

Defined Under Namespace

Classes: ConcurrencyError, ReadLock, WriteLock

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize ⇒ LockManager

Returns a new instance of LockManager.



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# File 'lib/spinoza/system/lock-manager.rb', line 88

def initialize
  @locks = {}
end

Instance Attribute Details

#locks ⇒ Object (readonly)

{ resource => WriteLock | ReadLock | nil, … } typically, resource == [table, key]



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# File 'lib/spinoza/system/lock-manager.rb', line 86

def locks
  @locks
end

Instance Method Details

#has_read_lock?(resource, txn) ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/spinoza/system/lock-manager.rb', line 159

def has_read_lock? resource, txn
  lock = locks[resource]
  lock.kind_of?(ReadLock) && lock.includes?(txn)
end

#has_write_lock?(resource, txn) ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/spinoza/system/lock-manager.rb', line 164

def has_write_lock? resource, txn
  lock = locks[resource]
  lock.kind_of?(WriteLock) && lock.includes?(txn)
end

#lock_read(resource, txn) ⇒ Object 



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# File 'lib/spinoza/system/lock-manager.rb', line 92

def lock_read resource, txn
  case lock = locks[resource]
  when nil
    locks[resource] = ReadLock.new(txn)
  when ReadLock, WriteLock
    lock.add txn
      # in WriteLock case, add the reader as a writer
      # (fails if not locked by txn)
  else raise
  end
end

#lock_write(resource, txn) ⇒ Object 



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# File 'lib/spinoza/system/lock-manager.rb', line 104

def lock_write resource, txn
  case lock = locks[resource]
  when nil
    locks[resource] = WriteLock.new(txn)
  when WriteLock
    lock.add txn
  when ReadLock
    raise ConcurrencyError, "#{resource} is locked: #{lock}"
  else raise
  end
end

#unlock_all(txn) ⇒ Object 



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# File 'lib/spinoza/system/lock-manager.rb', line 150

def unlock_all txn
  locks.delete_if do |resource, lock|
    if lock and lock.includes? txn
      lock.remove txn
      lock.unlocked?
    end
  end
end

#unlock_read(resource, txn) ⇒ Object 



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# File 'lib/spinoza/system/lock-manager.rb', line 116

def unlock_read resource, txn
  lock = locks[resource]
  case lock
  when nil
    raise ConcurrencyError, "#{resource} is not locked"
  when ReadLock, WriteLock
    begin
      lock.remove txn
      locks.delete resource if lock.unlocked?
    rescue ConcurrencyError => ex
      raise ConcurrencyError "#{resource}: #{ex.message}"
    end
  else raise
  end
end

#unlock_write(resource, txn) ⇒ Object 



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# File 'lib/spinoza/system/lock-manager.rb', line 132

def unlock_write resource, txn
  lock = locks[resource]
  case lock
  when ReadLock
    raise ConcurrencyError, "#{resource} is read locked: #{lock}"
  when nil
    raise ConcurrencyError, "#{resource} is not locked"
  when WriteLock
    begin
      lock.remove txn
      locks.delete resource if lock.unlocked?
    rescue ConcurrencyError => ex
      raise ConcurrencyError "#{resource}: #{ex.message}"
    end
  else raise
  end
end