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const crypto = require('crypto'),
sqlite3 = require('sqlite3'),
{ Client } = require('pg'),
async = require('async'),
iferr = require('iferr'),
EventEmitter = require('events').EventEmitter;
/**
Creates an object which allocates jobs across a number of instances.
@param {Object} options - Configuration options.
@param {'sqlite' | 'pg'} [options.db_type=sqlite] - Type of database to use.
@param {string} options.db_filename - (sqlite) Filename in which to store the allocations. You can use the same file in multiple `Atributo` objects, even across different processes. They will all make and see the same allocations.
@param {integer} [options.db_mode] - (sqlite) Mode to open the file in. See the [sqlite3](https://github.com/mapbox/node-sqlite3/wiki/API#new-sqlite3databasefilename-mode-callback) documentation.
@param {integer} [options.busy_wait=1000] - (sqlite) Number of milliseconds to wait before retrying if another `Atributo` object has the database file locked.
@param {Object} options.db - (pg) [`node-postgres` configuration](https://node-postgres.com/api/client).
*/
class Atributo extends EventEmitter
{
constructor(options)
{
super();
this._options = Object.assign(
{
db_type: 'sqlite',
busy_wait: 1000
}, options);
switch (this._options.db_type)
{
case 'sqlite':
this._db = new sqlite3.Database(this._options.db_filename,
this._options.db_mode);
this._db.on('open', () => this.emit('ready'));
this._db.on('close', () => this.emit('close'));
this._true = 1;
this._false = 0;
this._busy_code = 'SQLITE_BUSY';
break;
case 'pg':
this._db = new Client(this._options.db);
this._db.connect(err =>
{
if (err)
{
return this.emit('error', err);
}
this.emit('ready');
});
this._db.on('end', () => this.emit('close'));
this._true = true;
this._false = false;
this._busy_code = '40001';
break;
default:
throw new Error(`invalid database type: ${this._options.db_type}`);
}
this._db.on('error', err => this.emit('error', err));
// We need to queue queries on a db connection:
// https://github.com/mapbox/node-sqlite3/issues/304
// Alternative would be to create a separate connection
// for each query. The calling application can still do
// this if required (to achieve more parallelism) by
// creating many Atributo objects.
this._queue = async.queue((task, cb) => task(cb));
}
/**
Close the database file. Subsequent operations will fail.
@param {closeCallback} [cb] - Called once the database is closed.
*/
close(cb)
{
switch (this._options.db_type)
{
case 'sqlite':
this._db.close(cb);
break;
case 'pg':
this._db.end(cb);
break;
}
}
/**
Make an instance available for job allocation.
@param {string} instance_id - ID of the instance.
@param {availableCallback} cb - Called once the instance has been made available.
*/
available(instance_id, cb)
{
let b = this._busy(cb, () => this.available(instance_id, cb));
this._in_transaction(b, cb =>
{
this._queue.unshift(cb => async.waterfall(
[
cb =>
{
let sql;
switch (this._options.db_type)
{
case 'sqlite':
sql = 'INSERT OR IGNORE INTO instances VALUES ($1, $2);';
break;
case 'pg':
sql = 'INSERT INTO instances VALUES ($1, $2) ON CONFLICT DO NOTHING;'
break;
}
this._run(sql, [instance_id, this._true], cb);
},
cb =>
{
// Do this in a transaction so we don't error if someone else
// deletes the row here.
this._run('UPDATE instances SET available = $1 WHERE id = $2;',
[this._true, instance_id],
cb);
}
], cb), cb);
});
}
/**
Make an instance unavailable for job allocation.
@param {string} instance_id - ID of the instance.
@param {boolean} destroyed - If false, the instance won't be allocated any more jobs. If true, it is also removed from the database along with its existing job allocations.
@param {unavailableCallback} cb - Called once the instance has been made unavailable.
*/
unavailable(instance_id, destroyed, cb)
{
let b = this._busy(cb, () => this.unavailable(instance_id, destroyed, cb));
this._in_transaction(b, cb =>
{
let statements = [
cb =>
{
let sql;
switch (this._options.db_type)
{
case 'sqlite':
sql = 'INSERT OR IGNORE INTO instances VALUES ($1, $2);';
break;
case 'pg':
sql = 'INSERT INTO instances VALUES ($1, $2) ON CONFLICT DO NOTHING;'
break;
}
this._run(sql, [instance_id, this._false], cb);
},
cb =>
{
this._run('UPDATE instances SET available = $1 WHERE id = $2;',
[this._false, instance_id],
cb);
}
];
if (destroyed)
{
statements.push(
cb =>
{
this._run('DELETE FROM allocations WHERE instance = $1;',
[instance_id],
cb);
},
cb =>
{
this._run('DELETE FROM instances WHERE id = $1;',
[instance_id],
cb);
}
);
}
this._queue.unshift(cb => async.waterfall(statements, cb), cb);
});
}
/**
Get a list of instance IDs along with their availability.
@param {instancesCallback} cb - Called with the list of instances.
*/
instances(cb)
{
this._queue.push(cb => async.waterfall(
[
cb =>
{
this._all('SELECT * from instances;',
[],
cb);
},
(r, cb) =>
{
for (let row of r)
{
row.available = !!row.available;
}
cb(null, r);
}
], cb), this._busy(cb, () => this.instances(cb)));
}
/**
Allocate a job to an instance.
@param {string} job_id - ID of the job to allocate.
@param {allocateCallback} cb - Called with the ID of the instance to which the job was allocated, and whether the allocation was persisted to the database. The default allocator chooses the instance based on a hash of `job_id`. You can override the [`_allocate`](#atributo_allocate) function to provide a different allocator.
*/
allocate(job_id, cb)
{
let b = this._busy(cb, () => this.allocate(job_id, cb));
this._in_transaction(b, cb =>
{
this._queue.unshift(cb =>
{
this._get('SELECT instance FROM allocations WHERE job = $1;',
[job_id],
cb);
}, iferr(cb, r =>
{
if (r !== undefined)
{
return cb(null, r.instance, false);
}
this._queue.unshift(cb =>
{
this._all('SELECT id FROM instances WHERE available = $1;',
[this._true],
cb);
}, iferr(cb, r =>
{
if (r.length === 0)
{
return cb(new Error('no instances'));
}
this._queue.unshift(cb =>
{
this._allocate(job_id, r.map(row => row.id), cb);
}, iferr(cb, (instance_id, persist) =>
{
if (!persist)
{
return cb(null, instance_id, false);
}
this._queue.unshift(cb =>
{
this._run('INSERT INTO allocations VALUES ($1, $2);',
[job_id, instance_id],
cb);
}, iferr(cb, r =>
{
cb(null, instance_id, true);
}));
}));
}));
}));
});
}
/**
Remove a job allocation.
@param {string} job_id - ID of job to deallocate. If the job is allocated to an instance in the database, the allocation will be removed.
@param {deallocateCallback} cb - Called when the allocation has been removed.
*/
deallocate(job_id, cb)
{
this._queue.push(cb =>
{
this._run('DELETE FROM allocations WHERE job = $1;',
[job_id],
cb);
}, this._busy(cb, () => this.deallocate(job_id, cb)));
}
/**
Get whether an instance has jobs allocated to it.
@param {string} instance_id - ID of the instance.
@param {has_jobsCallback} cb - Receives whether there are jobs allocated to to the instance.
*/
has_jobs(instance_id, cb)
{
this._queue.push(cb => async.waterfall(
[
cb =>
{
this._get('SELECT count(*) FROM allocations WHERE instance = $1;',
[instance_id],
cb);
},
(r, cb) =>
{
let key;
switch (this._options.db_type)
{
case 'sqlite':
key = 'count(*)';
break;
case 'pg':
key = 'count';
break;
}
cb(null, r[key] > 0);
}
], cb), this._busy(cb, () => this.has_jobs(instance_id, cb)));
}
/**
Gets the jobs allocated to an instance.
@param {string} instance_id - ID of the instance.
@param {jobsCallback} cb - Called with a list of job IDs allocated to the instance.
*/
jobs(instance_id, cb)
{
this._queue.push(cb => async.waterfall(
[
cb =>
{
this._all('SELECT job from allocations WHERE instance = $1;',
[instance_id],
cb);
},
(r, cb) =>
{
cb(null, r.map(row => row.job));
}
], cb), this._busy(cb, () => this.jobs(instance_id, cb)));
}
/**
Gets the instance to which a job is allocated.
@param {string} job_id - ID of the job.
@param {instanceCallback} cb - Called with the ID of the instance to which the job is allocated, or `null`.
*/
instance(job_id, cb)
{
this._queue.push(cb =>
{
this._get('SELECT instance FROM allocations WHERE job = $1;',
[job_id],
iferr(cb, r =>
{
cb(null, r === undefined ? null : r.instance);
}));
}, this._busy(cb, () => this.instance(job_id, cb)));
}
_end_transaction(cb)
{
let f = (err, ...args) =>
{
if (err)
{
return this._queue.unshift(cb =>
{
this._run('ROLLBACK',
[],
cb);
}, this._busy(err2 => cb(err2 || err, ...args),
() => f(err, ...args),
true));
}
const cb2 = err => cb(err, ...args);
this._queue.unshift(cb =>
{
this._run('END TRANSACTION',
[],
cb);
}, this._options.db_type === 'sqlite' ?
this._busy(cb2,
() => f(err, ...args),
true) :
cb2);
};
return f;
}
_in_transaction(cb, f)
{
let isolation_level;
switch (this._options.db_type)
{
case 'sqlite':
isolation_level = ''; // SQLite transactions are serializable
break;
case 'pg':
isolation_level = 'ISOLATION LEVEL SERIALIZABLE';
break;
}
this._queue.push(cb2 =>
this._run(`BEGIN TRANSACTION ${isolation_level}`, [], cb2),
iferr(cb, () => f(this._end_transaction(cb))));
}
_busy(f, retry, block)
{
return (err, ...args) =>
{
if (err && (err.code === this._busy_code))
{
if (block)
{
return this._queue.unshift(cb => setTimeout(cb, this._options.busy_wait),
retry);
}
return setTimeout(retry, this._options.busy_wait);
}
f(err, ...args);
};
}
// Note: $1, $2 placeholders in SQL statements are PostgreSQL syntax.
// However, as long as they appear _in order_ (i.e. never $2 before $1)
// then they work in SQLite too. This is because when $ is used, SQLite
// binds first parameter in array to first $whatever in the statement,
// second parameter to second $something etc.
_run(sql, values, cb)
{
switch (this._options.db_type)
{
case 'sqlite':
this._db.run(sql, ...values, cb);
break;
case 'pg':
this._db.query(sql, values, iferr(cb, () => cb()));
break;
}
}
_all(sql, values, cb)
{
switch (this._options.db_type)
{
case 'sqlite':
this._db.all(sql, ...values, cb);
break;
case 'pg':
this._db.query(sql, values, iferr(cb, r => cb(null, r.rows)));
break;
}
}
_get(sql, values, cb)
{
switch (this._options.db_type)
{
case 'sqlite':
this._db.get(sql, ...values, cb);
break;
case 'pg':
this._db.query(sql, values, iferr(cb, r => cb(null, r.rows[0])));
break;
}
}
/**
The default job allocator algorithm. `job_id` is hashed, treated as an
integer and used as an index into the array of available instances.
Override this method to provide a different algorithm.
@param {string} job_id - ID of the job to allocate.
@param {string[]} instance_ids - IDs of available instances.
@param {_allocateCallback} cb - Your allocator method should call this once it's decided to which instance the job should be allocated.
*/
_allocate(job_id, instance_ids, cb)
{
let h = crypto.createHash('md5'); // not for security, just mapping
h.update(job_id);
let buf = h.digest();
cb(null, instance_ids[buf.readUInt32BE(0) % instance_ids.length], true);
}
}
exports.Atributo = Atributo;
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