met behulp van de postgresql gem async

De pg bibliotheek biedt volledige ondersteuning voor de asynchrone API van PostgreSQL. Ik heb een voorbeeld toegevoegd van hoe het te gebruiken voor de samples/ map:

#!/usr/bin/env ruby

require 'pg'

# This is a example of how to use the asynchronous API to query the
# server without blocking other threads. It's intentionally low-level;
# if you hooked up the PGconn#socket to some kind of reactor, you
# could make this much nicer.

TIMEOUT = 5.0 # seconds to wait for an async operation to complete
CONN_OPTS = {
    :host     => 'localhost',
    :dbname   => 'test',
    :user     => 'jrandom',
    :password => 'banks!stealUR$',
}

# Print 'x' continuously to demonstrate that other threads aren't
# blocked while waiting for the connection, for the query to be sent,
# for results, etc. You might want to sleep inside the loop or 
# comment this out entirely for cleaner output.
progress_thread = Thread.new { loop { print 'x' } }

# Output progress messages
def output_progress( msg )
    puts "\n>>> #{msg}\n"
end

# Start the connection
output_progress "Starting connection..."
conn = PGconn.connect_start( CONN_OPTS ) or 
    abort "Unable to create a new connection!"
abort "Connection failed: %s" % [ conn.error_message ] if
    conn.status == PGconn::CONNECTION_BAD

# Now grab a reference to the underlying socket so we know when the
# connection is established
socket = IO.for_fd( conn.socket )

# Track the progress of the connection, waiting for the socket to 
# become readable/writable before polling it
poll_status = PGconn::PGRES_POLLING_WRITING
until poll_status == PGconn::PGRES_POLLING_OK ||
      poll_status == PGconn::PGRES_POLLING_FAILED

    # If the socket needs to read, wait 'til it becomes readable to
    # poll again
    case poll_status
    when PGconn::PGRES_POLLING_READING
        output_progress "  waiting for socket to become readable"
        select( [socket], nil, nil, TIMEOUT ) or
            raise "Asynchronous connection timed out!"

    # ...and the same for when the socket needs to write
    when PGconn::PGRES_POLLING_WRITING
        output_progress "  waiting for socket to become writable"
        select( nil, [socket], nil, TIMEOUT ) or
            raise "Asynchronous connection timed out!"
    end

    # Output a status message about the progress
    case conn.status
    when PGconn::CONNECTION_STARTED
        output_progress "  waiting for connection to be made."
    when PGconn::CONNECTION_MADE
        output_progress "  connection OK; waiting to send."
    when PGconn::CONNECTION_AWAITING_RESPONSE
        output_progress "  waiting for a response from the server."
    when PGconn::CONNECTION_AUTH_OK
        output_progress "  received authentication; waiting for " +
                        "backend start-up to finish."
    when PGconn::CONNECTION_SSL_STARTUP
        output_progress "  negotiating SSL encryption."
    when PGconn::CONNECTION_SETENV
        output_progress "  negotiating environment-driven " +
                        "parameter settings."
    end

    # Check to see if it's finished or failed yet
    poll_status = conn.connect_poll
end

abort "Connect failed: %s" % [ conn.error_message ] unless 
    conn.status == PGconn::CONNECTION_OK

output_progress "Sending query"
conn.send_query( "SELECT * FROM pg_stat_activity" )

# Fetch results until there aren't any more
loop do
    output_progress "  waiting for a response"

    # Buffer any incoming data on the socket until a full result 
    # is ready. 
    conn.consume_input
    while conn.is_busy
        select( [socket], nil, nil, TIMEOUT ) or
            raise "Timeout waiting for query response."
        conn.consume_input
    end

    # Fetch the next result. If there isn't one, the query is 
    # finished
    result = conn.get_result or break

    puts "\n\nQuery result:\n%p\n" % [ result.values ]
end

output_progress "Done."
conn.finish

if defined?( progress_thread )
    progress_thread.kill
    progress_thread.join
end

Ik raad je aan de documentatie te lezen op de PQconnectStart functie en de Asynchrone opdrachtverwerking van de PostgreSQL-handleiding en vergelijk dat met het bovenstaande voorbeeld.

Ik heb EventMachine nog niet eerder gebruikt, maar als je hiermee een socket en callbacks kunt registreren voor wanneer het leesbaar/beschrijfbaar wordt, zou het vrij eenvoudig zijn om database-aanroepen erin te integreren.

Ik wilde de ideeën gebruiken in Ilya Grigorik's artikel over het gebruik van vezels om evented code op te schonen om de asynchrone API gebruiksvriendelijker te maken, maar dat is een heel eind. Ik heb wel een ticket openen om het te volgen als je geïnteresseerd/gemotiveerd bent om het zelf te doen.