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qlobber-fsq   

Shared file system queue for Node.js.

• Note: Version 12.1.0 supports direct producer-to-subscriber streams where the data doesn't go via the filesystem. See the direct_handler option to the QlobberFSQ constructor and the direct option to publish.
• Note: Version 9 can use shared memory LMAX Disruptors to speed things up on a single multi-core server.
• Supports pub-sub and work queues.
• Supports local file system for multi-core use.
• Tested with FraunhoferFS (BeeGFS) and CephFS for distributed use.
• Note: An alternative module, qlobber-pg, can be used when you need access from multiple hosts. It's API-compatible with qlobber-fsq and requires a PostgreSQL database.
• Highly configurable.
• Full set of unit tests, including stress tests.
• Use as a backend-less alternative to RabbitMQ, Redis pub-sub etc.
• Supports AMQP-like topics with single- and multi-level wildcards.
• Tested on Linux and Windows.

Example:

var QlobberFSQ = require('qlobber-fsq').QlobberFSQ;
var fsq = new QlobberFSQ({ fsq_dir: '/shared/fsq' });
fsq.subscribe('foo.*', function (data, info)
{
    console.log(info.topic, data.toString('utf8'));
    var assert = require('assert');
    assert.equal(info.topic, 'foo.bar');
    assert.equal(data, 'hello');
});
fsq.on('start', function ()
{
    this.publish('foo.bar', 'hello');
});

You can publish messages using a separate process if you like:

var QlobberFSQ = require('qlobber-fsq').QlobberFSQ;
var fsq = new QlobberFSQ({ fsq_dir: '/shared/fsq' });
fsq.stop_watching();
fsq.on('stop', function ()
{
    this.publish('foo.bar', 'hello');
});

Or use the streaming interface to read and write messages:

const { QlobberFSQ } = require('qlobber-fsq');
const fsq = new QlobberFSQ({ fsq_dir: '/shared/fsq' });
function handler(stream, info)
{
    const data = [];

    stream.on('readable', function ()
    {
        let chunk;
        while (chunk = this.read())
        {
            data.push(chunk);
        }
    });

    stream.on('end', function ()
    {
        const str = Buffer.concat(data).toString('utf8');
        console.log(info.topic, str);
        const assert = require('assert');
        assert.equal(info.topic, 'foo.bar');
        assert.equal(str, 'hello');
    });
}
handler.accept_stream = true;
fsq.subscribe('foo.*', handler);
fsq.on('start', function ()
{
    fsq.publish('foo.bar').end('hello');
});

The API is described here.

Installation

npm install qlobber-fsq

Limitations

• qlobber-fsq provides no guarantee that the order messages are given to subscribers is the same as the order in which the messages were written. If you want to maintain message order between readers and writers then you'll need to do it in your application (using ACKs, sliding windows etc). Alternatively, use the order_by_expiry constructor option to have messages delivered in order of the time they expire.

• qlobber-fsq does its best not to lose messages but in exceptional circumstances (e.g. process crash, file system corruption) messages may get dropped. You should design your application to be resilient against dropped messages.

• qlobber-fsq makes no assurances about the security or privacy of messages in transit or at rest. It's up to your application to encrypt messages if required.

• qlobber-fsq supports Node 6 onwards.

Distributed filesystems

Note: When using a distributed file system with qlobber-fsq, ensure that you synchronize the time and date on all the computers you're using.

FraunhoferFS (BeeGFS)

When using the FraunhoferFS distributed file system, set the following options in fhgfs-client.conf:

tuneFileCacheType             = none
tuneUseGlobalFileLocks        = true

qlobber-fsq has been tested with FraunhoferFS 2014.01 on Ubuntu 14.04 and FraunhoferFS 2012.10 on Ubuntu 13.10.

CephFS

qlobber-fsq has been tested with CephFS 0.80 on Ubuntu 14.04. Note that you'll need to upgrade your kernel to at least 3.14.1 in order to get the fix for a bug in CephFS.

How it works

Under the directory you specify for fsq_dir, qlobber-fsq creates the following sub-directories:

• staging Whilst it's being published, each message is written to a file in the staging area. The filename itself contains the message's topic, when it expires, whether it should be read by one subscriber or many and a random sequence of characters to make it unique.
• messages Once published to the staging area, each message is moved into this directory. qlobber-fsq actually creates a number of sub-directories (called buckets) under messages and distributes message between buckets according to the hash of their filenames. This helps to reduce the number of directory entries that have to be read when a single message is written.
• topics If a message's topic is long, a separate topic file is created for it in this directory.
• update This contains one file, UPDATE, which is updated with a random sequence of bytes (called a stamp) every time a message is moved into the messages directory. UPDATE contains a separate stamp for each bucket.

qlobber-fsq reads UPDATE at regular intervals to determine whether a new message has been written to a bucket. If it has then it processes each filename in the bucket's directory listing.

If the expiry time in the filename has passed then it deletes the message.

If the filename indicates the message can be read by many subscribers:

• If it's processed this filename before then stop processing this filename.
• If the topic in the filename matches any subscribers then call each subscriber with the file's content. It uses qlobber to pattern match topics to subscribers.
• Remember that we've processed the filename.

If the filename indicates the message can be read by only one subscriber (i.e. work queue semantics):

• Try to lock the file using flock. If it fails to lock the file then stop processing this filename.
• If the topic in the filename matches any subscribers then call one subscriber with the file's content.
• Truncate and delete the file before unlocking it. We truncate the file in case of directory caching.

Licence

MIT

Test

To run the default tests:

grunt test [--fsq-dir=<path>] [--getdents_size=<buffer size>] [--disruptor]

If you don't specify --fsq-dir then the default will be used (a directory named fsq in the test directory).

If you specify --getdents_size then use of getdents will be included in the tests.

If you specify --disruptor then use of shared memory LMAX Disruptors will be included in the tests.

To run the stress tests (multiple queues in a single Node process):

grunt test-stress [--fsq-dir=<path>] [--disruptor]

To run the multi-process tests (each process publishing and subscribing to different messages):

grunt test-multi [--fsq-dir=<path>] [--queues=<number of queues>] [--disruptor]

If you omit --queues then one process will be created per core (detected with os.cpus()).

To run the distributed tests (one process per remote host, each one publishing and subscribing to different messages):

grunt test-multi --fsq-dir=<path> --remote=<host1> --remote=<host2>

You can specify as many remote hosts as you like. The test uses cp-remote to run a module on each remote host. Make sure on each host:

• The qlobber-fsq module is installed at the same location.
• Mount the same distributed file system on the directory you specify for --fsq-dir. FraunhoferFS and CephFS are the only distributed file systems currently supported.

Please note the distributed tests don't run on Windows.

Lint

grunt lint

Code Coverage

grunt coverage [--fsq-dir=<path>]

c8 results are available here.

Coveralls page is here.

Benchmarks

To run the benchmark:

grunt bench [--fsq-dir=<path>] \
            --rounds=<number of rounds> \
            --size=<message size> \
            --ttl=<message time-to-live in seconds> \
            [--disruptor] \
            [--num_elements=<number of disruptor elements>] \
            [--element_size=<disruptor element size>] \
            [--bucket_stamp_size=<number of bytes to write to UPDATE file] \
            [--getdents_size=<buffer size>] \
            [--ephemeral] \
            [--refresh_ttl=<period between expiration check in seconds>] \
            (--queues=<number of queues> | \
             --remote=<host1> --remote=<host2> ...)

If you don't specify --fsq-dir then the default will be used (a directory named fsq in the bench directory).

If you provide at least one --remote=<host> argument then the benchmark will be distributed across multiple hosts using cp-remote. Make sure on each host:

• The qlobber-fsq module is installed at the same location.
• Mount the same distributed file system on the directory you specify for --fsq-dir. FraunhoferFS and CephFS are the only distributed file systems currently supported.

API

<a name="tableofcontents"></a>

Constructor

• <a name="toc_qlobberfsqoptions"></a>QlobberFSQ

Publish and subscribe

• <a name="toc_qlobberfsqprototypesubscribetopic-handler-options-cb"></a><a name="toc_qlobberfsqprototype"></a>QlobberFSQ.prototype.subscribe
• <a name="toc_qlobberfsqprototypeunsubscribetopic-handler-cb"></a>QlobberFSQ.prototype.unsubscribe
• <a name="toc_qlobberfsqprototypepublishtopic-payload-options-cb"></a>QlobberFSQ.prototype.publish

Lifecycle

• <a name="toc_qlobberfsqprototypestop_watchingcb"></a>QlobberFSQ.prototype.stop_watching
• <a name="toc_qlobberfsqprototyperefresh_now"></a>QlobberFSQ.prototype.refresh_now
• <a name="toc_qlobberfsqprototypeforce_refresh"></a>QlobberFSQ.prototype.force_refresh
• <a name="toc_qlobberfsqget_num_bucketsbucket_base-bucket_num_chars"></a>QlobberFSQ.get_num_buckets

Events

• <a name="toc_qlobberfsqeventsstart"></a><a name="toc_qlobberfsqevents"></a>QlobberFSQ.events.start
• <a name="toc_qlobberfsqeventsstop"></a>QlobberFSQ.events.stop
• <a name="toc_qlobberfsqeventserrorerr"></a>QlobberFSQ.events.error
• <a name="toc_qlobberfsqeventswarningerr"></a>QlobberFSQ.events.warning
• <a name="toc_qlobberfsqeventssingle_disablederr"></a>QlobberFSQ.events.single_disabled
• <a name="toc_qlobberfsqeventsgetdents_disablederr"></a>QlobberFSQ.events.getdents_disabled

QlobberFSQ([options])

Creates a new QlobberFSQ object for publishing and subscribing to a file system queue.

Parameters:

• {Object} [options] Configures the file system queue. Valid properties are listed below:

  • {String} fsq_dir The path to the file system queue directory. Note that the following sub-directories will be created under this directory if they don't exist: messages, staging, topics and update. Defaults to a directory named fsq in the qlobber-fsq module directory.

  • {Boolean} encode_topics Whether to hex-encode message topics. Because topic strings form part of message filenames, they're first hex-encoded. If you can ensure that your message topics contain only valid filename characters, set this to false to skip encoding. Defaults to true.

  • {Integer} split_topic_at Maximum number of characters in a short topic. Short topics are contained entirely in a message's filename. Long topics are split so the first split_topic_at characters go in the filename and the rest are written to a separate file in the topics sub-directory. Obviously long topics are less efficient. Defaults to 200, which is the maximum for most common file systems. Note: if your fsq_dir is on an ecryptfs file system then you should set split_topic_at to 100.

  • {Integer} bucket_base, {Integer} bucket_num_chars Messages are distributed across different buckets for efficiency. Each bucket is a sub-directory of the messages directory. The number of buckets is determined by the bucket_base and bucket_num_chars options. bucket_base is the radix to use for bucket names and bucket_num_chars is the number of digits in each name. For example, bucket_base: 26 and bucket_num_chars: 4 results in buckets 0000 through pppp. Defaults to base_base: 16 and bucket_num_chars: 2 (i.e. buckets 00 through ff). The number of buckets is available as the num_buckets property of the QlobberFSQ object.

  • {Integer} bucket_stamp_size The number of bytes to write to the UPDATE file when a message is published. The UPDATE file (in the update directory) is used to determine whether any messages have been published without having to scan all the bucket directories. Each bucket has a section in the UPDATE file, bucket_stamp_size bytes long. When a message is written to a bucket, its section is filled with random bytes. Defaults to 32. If you set this to 0, the UPDATE file won't be written to and all the bucket directories will be scanned even if no messages have been published.

  • {Integer} flags Extra flags to use when reading and writing files. You shouldn't need to use this option but if you do then it should be a bitwise-or of values in the (undocumented) Node constants module (e.g. constants.O_DIRECT | constants.O_SYNC). Defaults to 0.

  • {Integer} unique_bytes Number of random bytes to append to each message's filename (encoded in hex), in order to avoid name clashes. Defaults to 16. If you increase it (or change the algorithm to add some extra information like the hostname), be sure to reduce split_topic_at accordingly.

  • {Integer} single_ttl Default time-to-live (in milliseconds) for messages which should be read by at most one subscriber. This value is added to the current time and the resulting expiry time is put into the message's filename. After the expiry time, the message is ignored and deleted when convenient. Defaults to 1 hour.

  • {Integer} multi_ttl Default time-to-live (in milliseconds) for messages which can be read by many subscribers. This value is added to the current time and the resulting expiry time is put into the message's filename. After the expiry time, the message is ignored and deleted when convenient. Defaults to 1 minute.

  • {Integer} poll_interval qlobber-fsq reads the UPDATE file at regular intervals to check whether any messages have been written. poll_interval is the time (in milliseconds) between each check. Defaults to 1 second.

  • {Boolean} notify Whether to use fs.watch to watch for changes to the UPDATE file. Note that this will be done in addition to reading it every poll_interval milliseconds because fs.watch (inotify underneath) can be unreliable, especially under high load. Defaults to true.

  • {Integer} retry_interval Some I/O operations can fail with an error indicating they should be retried. retry_interval is the time (in milliseconds) to wait before retrying. Defaults to 1 second.

  • {Integer} message_concurrency The number of messages in each bucket to process at once. Defaults to 1.

  • {Integer} bucket_concurrency The number of buckets to process at once. Defaults to 1.

  • {Integer} handler_concurrency By default, a message is considered handled by a subscriber only when all its data has been read. If you set handler_concurrency to non-zero, a message is considered handled as soon as a subscriber receives it. The next message will then be processed straight away. The value of handler_concurrency limits the number of messages being handled by subscribers at any one time. Defaults to 0 (waits for all message data to be read).

  • {Boolean} order_by_expiry Pass messages to subscribers in order of their expiry time. If true then bucket_base and bucket_num_chars are forced to 1 so messages are written to a single bucket. Defaults to false.

  • {Boolean} dedup Whether to ensure each handler function is called at most once when a message is received. Defaults to true.

  • {Boolean} single Whether to process messages meant for at most one subscriber (across all QlobberFSQ objects), i.e. work queues. This relies on the optional dependency fs-ext. Defaults to true if fs-ext is installed, otherwise false (in which case a single_disabled event will be emitted).

  • {String} separator The character to use for separating words in message topics. Defaults to ..

  • {String} wildcard_one The character to use for matching exactly one word in a message topic to a subscriber. Defaults to *.

  • {String} wildcard_some The character to use for matching zero or more words in a message topic to a subscriber. Defaults to #.

  • {Integer} getdents_size If positive, use getdents to enumerate messages in bucket directories. getdents_size is the buffer size to use with getdents. Otherwise, use fs.readdir (which is the default). If getdents is requested but unavailable, a getdents_disabled event will be emitted.

  • {Function (info, handlers, cb(err, ready, filtered_handlers)) | Array} filter Function called before each message is processed.

    • You can use this to filter the subscribed handler functions to be called for the message (by passing the filtered list as the third argument to cb).

    • If you want to ignore the message at this time then pass false as the second argument to cb. filter will be called again later with the same message.

    • Defaults to a function which calls cb(null, true, handlers).

    • handlers is an ES6 Set, or array if options.dedup is falsey.

    • filtered_handlers should be an ES6 Set, or array if options.dedup is falsey. If not, new Set(filtered_handlers) or Array.from(filtered_handlers) will be used to convert it.

    • You can supply an array of filter functions - each will be called in turn with the filtered_handlers from the previous one.

    • An array containing the filter functions is also available as the filters property of the QlobberFSQ object and can be modified at any time.

  • {Function (bucket)} [get_disruptor] You can speed up message processing on a single multi-core server by using shared memory LMAX Disruptors. Message metadata and (if it fits) payload will be sent through the Disruptor. get_disruptor will be called for each bucket number and should return the Disruptor to use for that bucket or null. The same disruptor can be used for more than one bucket if you wish.

  • {Integer} refresh_ttl If you use a shared memory LMAX Disruptor for a bucket (see get_disruptor above), notification of new messages in the bucket is received through the Disruptor. However, checking for expired messages still needs to read the filesystem. refresh_ttl is the time (in milliseconds) between checking for expired messages when a Disruptor is in use. Defaults to 10 seconds.

  • {Integer} disruptor_spin_interval If a Disruptor is shared across multiple buckets or multiple QlobberFSQ instances, contention can occur when publishing a message. In this case publish will try again until it succeeds. disruptor_spin_interval is the time (in milliseconds) to wait before retrying. Defaults to 0.

  • {Object} [direct_handler] Object with the following methods, used for transferring messages direct from publisher to subscribers without writing them to disk:

    • {Function (filename, direct)} get_stream_for_publish Called by publish when truthy options.direct is passed to it instead of writing data to disk. This method receives the name of the file to which data would have been written plus the value of options.direct that was passed to publish. Whatever it returns will be returned by the call to publish.

    • {Function (filename)} get_stream_for_subscribers Called when a stream published by calling publish with truthy options.direct needs to be given to subscribers. It receives the name of the file to which data would have been written. It must return a Readable stream.

    • {Function (filename, stream)} publish_stream_destroyed Called when a stream returned by get_stream_for_publish() has been destroyed or the message has expired. It receives the name of the file passed to `get_stream_for_publish() and the destroyed stream.

    • {Function (filename)} publish_stream_expired Called when a stream returned by get_stream_for_publish() has expired and should be destroyed. It receives the name of the file passed to get_stream_for_publish().

    • {Function (filename, stream)} subscriber_stream_destroyed Called when a stream returned by get_stream_for_subscribers() has been destroyed or the message has expired. It receives the name of the file passed to get_stream_for_subscribers() and the destroyed stream.

    • {Function (filename)} subscriber_stream_ignored Called when a stream published by calling publish with truthy options.direct doesn't have any subscribers. It receives the name of the file to which data would have been written.

_{Go: TOC}

<a name="qlobberfsqprototype"></a>

QlobberFSQ.prototype.subscribe(topic, handler, [options], [cb])

Subscribe to messages in the file system queue.

Parameters:

• {String} topic Which messages you're interested in receiving. Message topics are split into words using . as the separator. You can use * to match exactly one word in a topic or # to match zero or more words. For example, foo.* would match foo.bar whereas foo.# would match foo, foo.bar and foo.bar.wup. Note you can change the separator and wildcard characters by specifying the separator, wildcard_one and wildcard_some options when constructing QlobberFSQ objects. See the qlobber documentation for more information.

• {Function} handler Function to call when a new message is received on the file system queue and its topic matches against topic. handler will be passed the following arguments:

  • {Readable|Buffer} data Readable stream or message content as a Buffer. By default you'll receive the message content. If handler has a property accept_stream set to a truthy value then you'll receive a stream. Note that all subscribers will receive the same stream or content for each message. You should take this into account when reading from the stream. The stream can be piped into multiple Writable streams but bear in mind it will go at the rate of the slowest one.

  • {Object} info Metadata for the message, with the following properties:

    • {String} fname Name of the file in which the message is stored.
    • {String} path Full path to the file in which the message is stored.
    • {String} topic Topic the message was published with.
    • {String} [topic_path] Full path to the file in which the topic overspill is stored (only present if the topic is too long to fit in the file name).
    • {Integer} expires When the message expires (number of milliseconds after 1 January 1970 00:00:00 UTC).
    • {Boolean} single Whether this message is being given to at most one subscriber (across all QlobberFSQ objects).
    • {Integer} size Message size in bytes.

  • {Function} done Function to call once you've handled the message. Note that calling this function is only mandatory if info.single === true, in order to delete and unlock the file. done takes two arguments:

    • {Object} err If an error occurred then pass details of the error, otherwise pass null or undefined.
    • {Function} [finish] Optional function to call once the message has been deleted and unlocked, in the case of info.single === true, or straight away otherwise. It will be passed the following argument:
      • {Object} err If an error occurred then details of the error, otherwise null.

• {Object} [options] Optional settings for this subscription:

  • {Boolean} subscribe_to_existing If true then handler will be called with any existing, unexpired messages that match topic, as well as new ones. Note that handler will only receive new streams that were published by calling publish with truthy options.direct, not existing direct streams. Defaults to false (only new messages).

• {Function} [cb] Optional function to call once the subscription has been registered. This will be passed the following argument:

  • {Object} err If an error occurred then details of the error, otherwise null.

_{Go: TOC | QlobberFSQ.prototype}

QlobberFSQ.prototype.unsubscribe([topic], [handler], [cb])

Unsubscribe from messages in the file system queue.

Parameters:

• {String} [topic] Which messages you're no longer interested in receiving via the handler function. This should be a topic you've previously passed to subscribe. If topic is undefined then all handlers for all topics are unsubscribed.
• {Function} [handler] The function you no longer want to be called with messages published to the topic topic. This should be a function you've previously passed to subscribe. If you subscribed handler to a different topic then it will still be called for messages which match that topic. If handler is undefined, all handlers for the topic topic are unsubscribed.
• {Function} [cb] Optional function to call once handler has been unsubscribed from topic. This will be passed the following argument:
  • {Object} err If an error occurred then details of the error, otherwise null.

_{Go: TOC | QlobberFSQ.prototype}

QlobberFSQ.prototype.publish(topic, [payload], [options], [cb])

Publish a message to the file system queue.

Parameters:

• {String} topic Message topic. The topic should be a series of words separated by . (or the separator character you provided to the QlobberFSQ constructor). Topic words can contain any character, unless you set encode_topics to false in the QlobberFSQ constructor. In that case they can contain any valid filename character for your file system, although it's probably sensible to limit it to alphanumeric characters, -, _ and ..

• {String | Buffer} [payload] Message payload. If you don't pass a payload then publish will return a Writable stream for you to write the payload into.

• {Object} [options] Optional settings for this publication:

  • {Boolean} single If true then the message will be given to at most one interested subscriber, across all QlobberFSQ objects scanning the file system queue. Otherwise all interested subscribers will receive the message (the default).

  • {Integer} ttl Time-to-live (in milliseconds) for this message. If you don't specify anything then single_ttl or multi_ttl (provided to the QlobberFSQ constructor) will be used, depending on the value of single. After the time-to-live for the message has passed, the message is ignored and deleted when convenient.

  • {String} encoding If payload is a string, the encoding to use when writing it out to the message file. Defaults to utf8.

  • {Integer} mode The file mode (permissions) to set on the message file. Defaults to octal 0666 (readable and writable to everyone).

  • {Function} hasher A hash function to use for deciding into which bucket the message should be placed. The hash function should return a Buffer at least 4 bytes long. It defaults to running md5 on the message file name. If you supply a hasher function it will be passed the following arguments:

    • {String} fname Message file name.
    • {Integer} expires When the message expires (number of milliseconds after 1 January 1970 00:00:00 UTC).
    • {String} topic Message topic.
    • {String|Buffer} payload Message payload.
    • {Object} options The optional settings for this publication.

  • {Integer} bucket Which bucket to write the message into, instead of using hasher to calculate it.

  • {Boolean} ephemeral This applies only if a shared memory LMAX Disruptor is being used for the message's bucket (see the get_disruptor option to the QlobberFSQ constructor). By default, the message is written both to the Disruptor and the filesystem. If ephemeral is truthy, the message is written only to the Disruptor.

    • If the Disruptor's elements aren't large enough to contain the message's metadata, the message won't be written to the Disruptor and cb (below) will receive an error with a property code equal to the string buffer-too-small.

    • However, if the Disruptor's elements aren't large enough for the message's payload, the message will be written to disk. The amount of space available in the Disruptor for the payload can be found via the ephemeral_size property on the stream returned by this function. If your message won't fit and you don't want to write it to disk, emit an error event on the stream without ending it.

  • {Any} direct Defaults to false. If truthy:

    • Writes an empty message to disk instead of any data.
    • Calls the direct_handler.get_stream_for_publish() method that was passed to the QlobberFSQ constructor. It will be passed the name of the file to which data would otherwise have been written and the value of direct.
    • Returns the value that direct_handler.get_stream_for_publish() returns.
    • Ignores single (i.e. publish to all interested subscribers).

• {Function} [cb] Optional function to call once the message has been written to the file system queue. This will be called after the message has been moved into its bucket and is therefore available to subscribers in any QlobberFSQ object scanning the queue. It will be passed the following arguments:

  • {Object} err If an error occurred then details of the error, otherwise null.

  • {Object} info Metadata for the message. See subscribe for a description of info's properties.

Return:

{Stream | undefined} A Writable stream if no payload was passed, otherwise undefined.

_{Go: TOC | QlobberFSQ.prototype}

QlobberFSQ.prototype.stop_watching([cb])

Stop scanning for new messages.

Parameters:

• {Function} [cb] Optional function to call once scanning has stopped. Alternatively, you can listen for the stop event.

_{Go: TOC | QlobberFSQ.prototype}

QlobberFSQ.prototype.refresh_now()

Check the UPDATE file now rather than waiting for the next periodic check to occur

_{Go: TOC | QlobberFSQ.prototype}

QlobberFSQ.prototype.force_refresh()

Scan for new messages in the messages sub-directory without checking whether the UPDATE file has changed.

_{Go: TOC | QlobberFSQ.prototype}

QlobberFSQ.get_num_buckets(bucket_base, bucket_num_chars)

Given a radix to use for characters in bucket names and the number of digits in each name, return the number of buckets that can be represented.

Parameters:

• {Integer} bucket_base Radix for bucket name characters.
• {Integer} bucket_num_chars Number of characters in bucket names.

Return:

{Integer} The number of buckets that can be represented.

_{Go: TOC | QlobberFSQ}

<a name="qlobberfsqevents"></a>

QlobberFSQ.events.start()

start event

QlobberFSQ objects fire a start event when they're ready to publish messages. Don't call publish until the start event is emitted or the message may be dropped. You can subscribe to messages before start is fired, however.

A start event won't be fired after a stop event.

_{Go: TOC | QlobberFSQ.events}

QlobberFSQ.events.stop()

stop event

QlobberFSQ objects fire a stop event after you call stop_watching and they've stopped scanning for new messages. Messages already read may still be being processed, however.

_{Go: TOC | QlobberFSQ.events}

QlobberFSQ.events.error(err)

error event

QlobberFSQ objects fire an error event if an error occurs before start is emitted. The QlobberFSQ object is unable to continue at this point and is not scanning for new messages.

Parameters:

• {Object} err The error that occurred.

_{Go: TOC | QlobberFSQ.events}

QlobberFSQ.events.warning(err)

warning event

QlobberFSQ objects fire a warning event if an error occurs after start is emitted. The QlobberFSQ object will still be scanning for new messages after emitting a warning event.

Parameters:

• {Object} err The error that occurred.

_{Go: TOC | QlobberFSQ.events}

QlobberFSQ.events.single_disabled(err)

single_disabled event

QlobberFSQ objects fire a single_disabled event if they can't support work queue semantics.

Parameters:

• {Object} err The error that caused single-subscriber messages not to be supported.

_{Go: TOC | QlobberFSQ.events}

QlobberFSQ.events.getdents_disabled(err)

getdents_disabled event

QlobberFSQ objects fire a getdents_disabled event if they can't support enumerating bucket directories using getdents.

Parameters:

• {Object} err The error that caused getdents to be unavailable.

_{Go: TOC | QlobberFSQ.events}

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