Class: ConnectionPool

Inherits:
Object show all
Defined in:
lib/sequel_core/connection_pool.rb

Overview

A ConnectionPool manages access to database connections by keeping multiple connections and giving threads exclusive access to each connection.

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(opts = {}, &block) ⇒ ConnectionPool

Constructs a new pool with a maximum size. If a block is supplied, it is used to create new connections as they are needed.

pool = ConnectionPool.new(:max_connections=>10) {MyConnection.new(opts)}

The connection creation proc can be changed at any time by assigning a Proc to pool#connection_proc.

pool = ConnectionPool.new(:max_connections=>10)
pool.connection_proc = proc {MyConnection.new(opts)}

The connection pool takes the following options:

  • :max_connections - The maximum number of connections the connection pool will open (default 4)

  • :pool_convert_exceptions - Whether to convert non-StandardError based exceptions to RuntimeError exceptions (default true)

  • :pool_reuse_connections - Which strategy to follow in regards to reusing connections:

    • :always - Always reuse a connection that belongs to the same thread

    • :allow - Only reuse a connection that belongs to the same thread if another cannot be acquired immediately (default)

    • :last_resort - Only reuse a connection that belongs to the same thread if the pool timeout has expired

    • :never - Never reuse a connection that belongs to the same thread

  • :pool_sleep_time - The amount of time to sleep before attempting to acquire a connection again (default 0.001)

  • :pool_timeout - The amount of seconds to wait to acquire a connection before raising a PoolTimeoutError (default 5)



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# File 'lib/sequel_core/connection_pool.rb', line 56

def initialize(opts = {}, &block)
  @max_size = opts[:max_connections] || 4
  @mutex = Mutex.new
  @connection_proc = block

  @available_connections = []
  @allocated = []
  @created_count = 0
  @timeout = opts[:pool_timeout] || 5
  @sleep_time = opts[:pool_sleep_time] || 0.001
  @reuse_connections = opts[:pool_reuse_connections] || :allow
  @convert_exceptions = opts.include?(:pool_convert_exceptions) ? opts[:pool_convert_exceptions] : true
end

Instance Attribute Details

#allocated ⇒ Object (readonly)

An array of connections currently being used



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# File 'lib/sequel_core/connection_pool.rb', line 6

def allocated
  @allocated
end

#available_connections ⇒ Object (readonly)

An array of connections opened but not currently used



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# File 'lib/sequel_core/connection_pool.rb', line 9

def available_connections
  @available_connections
end

#connection_proc ⇒ Object

The proc used to create a new database connection.



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# File 'lib/sequel_core/connection_pool.rb', line 12

def connection_proc
  @connection_proc
end

#created_count ⇒ Object (readonly) Also known as: size

The total number of connections opened, should be equal to available_connections.length + allocated.length



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# File 'lib/sequel_core/connection_pool.rb', line 17

def created_count
  @created_count
end

#max_size ⇒ Object (readonly)

The maximum number of connections.



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# File 'lib/sequel_core/connection_pool.rb', line 21

def max_size
  @max_size
end

#mutex ⇒ Object (readonly)

The mutex that protects access to the other internal vairables. You must use this if you want to manipulate the variables safely.



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# File 'lib/sequel_core/connection_pool.rb', line 25

def mutex
  @mutex
end

Instance Method Details

#disconnect(&block) ⇒ Object

Removes all connection currently available, optionally yielding each connection to the given block. This method has the effect of disconnecting from the database. Once a connection is requested using #hold, the connection pool creates new connections to the database.



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# File 'lib/sequel_core/connection_pool.rb', line 122

def disconnect(&block)
  @mutex.synchronize do
    @available_connections.each {|c| block[c]} if block
    @available_connections = []
    @created_count = @allocated.size
  end
end

#hold ⇒ Object

Chooses the first available connection, or if none are available, creates a new connection. Passes the connection to the supplied block:

pool.hold {|conn| conn.execute('DROP TABLE posts')}

Pool#hold can be re-entrant, meaning it can be called recursively in the same thread without blocking if the :pool_reuse_connections option was set to :always or :allow. Depending on the :pool_reuse_connections option you may get the connection currently used by the thread or a new connection.

If no connection is immediately available and the pool is already using the maximum number of connections, Pool#hold will block until a connection is available or the timeout expires. If the timeout expires before a connection can be acquired, a Sequel::Error::PoolTimeoutError is raised.



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# File 'lib/sequel_core/connection_pool.rb', line 85

def hold
  begin
    t = Thread.current
    time = Time.new
    timeout = time + @timeout
    sleep_time = @sleep_time
    reuse = @reuse_connections
    if (reuse == :always) && (conn = owned_connection(t))
      return yield(conn)
    end
    reuse = reuse == :allow ? true : false
    until conn = acquire(t)
      if reuse && (conn = owned_connection(t))
        return yield(conn)
      end
      if Time.new > timeout
        if (@reuse_connections == :last_resort) && (conn = owned_connection(t))
          return yield(conn)
        end
        raise(::Sequel::Error::PoolTimeoutError)
      end
      sleep sleep_time
    end
    begin
      yield conn
    ensure
      release(t, conn)
    end
  rescue Exception => e
    raise(@convert_exceptions && !e.is_a?(StandardError) ? RuntimeError.new(e.message) : e)
  end
end