query function breaks Promises

[trailsandtribulations]

Promises work great on regular pg. however, in pg-native, a resolve from a connect works fine, but resolve from query for some reason does not work at all.

here is the simplest test case ( using node --harmony --use_strict test.js):

// test.js

'use strict';

const Client = require('pg-native')

exports.testQuery = function(cl) {
  return new Promise( (resolve,reject) => {
    cl.query( 'select 1 as col', (err,rows) => {
      if( err ) return reject( err );
      console.log( 'selected '+rows[0].col );
      // resolve is called, but does not get to the then()
      resolve( rows[0].col );
    });
  });
}
exports.testing = function() {
  console.log( 'testing' );
  let client = new Client();
  client.connect( 'port = 6432 dbname = react', err => {
    if( err ) return console.log( 'conn err: '+err );
    console.log( 'connected' );
    exports.testQuery(client)
    .then( x => console.log('resolved x='+x) )
    .catch( x => console.log( 'err='+x ) ); 
   });
}

exports.testing();

[trailsandtribulations]

ran same test as above using prepare instead of query and got same results - the Promise's resolve() not passing to the Promise's then()

[trailsandtribulations]

here is the same test using pg = require('pg').native - this works fine

// test.pg.js
'use strict';
const pg = require('pg').native;
exports.testQuery = function(cl) {
  return new Promise( (resolve,reject) => {
    cl.query( 'select 1 as col', (err,result) => {
      if( err ) return reject( err );
      console.log( 'selected '+result.rows[0].col );
      resolve( result.rows[0].col );
    });
  });
}
exports.testing = function() {
  console.log( 'testing' );
  const connParams = {... };
  let client = new pg.Client( connParams );
  client.connect( err => {
    if( err ) return console.log( 'conn err: '+err );
    console.log( 'connected' );
    exports.testQuery(client)
      .then( x => { console.log('select x='+x); client.end(); } )
      .catch( err => { console.log( 'err='+err ); client.end(); } ); 
   });
}
exports.testing();

[brianc]

I don't use promises - care to dive into the code a bit here & see if you can figure out what's causing the issue?

[jacott]

There is something definitely wrong with the client.query function; if the client is ended after the query responds then the promise -- and the http server listen -- work. It may be a bug in node-libpq or in the c library itself. I'll try and isolate it some more.

[jacott]

calling client.pq.stopReader is enough to stop blocking the promise and the http server. Maybe node-libpq needs to have more of the read logic in another thread?

[jacott]

This bug* does not happen on node 0.10.38. It might be some bug in uv_poll_

* At least for the http server example in #21 since promises aren't in node 0.10

[trailsandtribulations]

for what it's worth, after reporting this, I wrote a new Promise-base node module based on node-libpq, https://github.com/trailsandtribulations/PrPq. the uv_poll code lifted from from node-pg.

it works with no problem, howbeit a bit slower than pg.

On Wed, Jun 3, 2015 at 8:14 AM, Geoff Jacobsen [email protected] wrote:

This bug* does not happen on node 0.10.38. It might be some bug in uv_poll_

• At least for the http server example in #21 https://github.com/brianc/node-pg-native/issues/21 since promises aren't in node 0.10

— Reply to this email directly or view it on GitHub https://github.com/brianc/node-pg-native/issues/16#issuecomment-108149403 .

[trailsandtribulations]

more testing from my PrPq. Promises no longer work when another service, in this case nodejs-websocket, is enabled. changed consume(): instead of startReader() messaging now using setTimeout() polling. works successfully. heavy load benchmark about the same.

[brianc]

Hmmm...I definitely wouldn't recommend using a setTimeout instead of startReader(). startReader() actually listens on the socket with libuv and gets alerted when the socket actual has data on it. setTimeout is a pretty epic hack....akin to reading of an http server's net socket with setTimeout or something.

Question...does this bug manifest with other versions of promises? Like bluebird or Q or whatever? Not very familiar w/ them but seems strange this hasn't been encountered before.

@jacott are you saying this prevents an http server from binding as well? Do you have an example of this causing an issue without promises?

[jacott]

@brianc see issue #21 for an example

[trailsandtribulations]

@brianc - have not tried with other Promise systems - running node --harmony --use_strict. assume that, in the end, this stuff will work.

agree that setTimeout() is epic hack. but in the end, once all working, will revert to sanity.

here's the consume() - this is not to say startReader() etc was impeccable to begin with:

PrPq.prototype._consume = () => {
  let pq = this;
  // if not busy, nothing to consume
  if( !pq._conn.libpq.isBusy() ) return Promise.resolve( pq );
  // KLUDGE
  return new Promise( (resolve,reject) => {
    function consume() {
      if( !pq._conn.libpq.consumeInput() ) return reject( pq._conn.libpq.errorMessage() );
      if( !pq._conn.libpq.isBusy() ) return resolve( pq );
      setTimeout( consume );
    }
    consume();
  } );
  //
  /* startReader() to listen to 'readable' events
  return new Promise( (resolve,reject) => {
    pq._conn.libpq.startReader();
    pq._conn.libpq.on('readable', function() {
      // consume input
      if( !pq._conn.libpq.consumeInput() ) return reject( pq._conn.libpq.errorMessage() );
      // note: consuming a 2nd buffer of input later...
      if(pq._conn.libpq.isBusy()) return;
     
      // release listener, stop watcher 
      //~pq._conn.libpq.removeListener('readable', onReadable);
      pq._conn.libpq.removeAllListeners('readable');
      pq._conn.libpq.stopReader();
      // done
      resolve( pq );
    });
  });
  */
}