Moses Nakamura


Posted August 12, 2014

Release notes

We’re experimenting with a new form of release notes, so that it’s easier to get context on what’s going on in Finagle-land, especially with an eye to letting consumers see what the latest and greatest features are, and providing a little more context around what’s going on.

If you have questions about something you see in the changelogs that we didn’t mention in the expanded release notes, please feel free to email me and ask for a clarification.

At a broader level, we’d also like to mention that we’re interested in improving Java compatibility, so if you’re having trouble using one of our APIs from Java, please let us know.

New versions



We made a couple of big changes to Buf, our byte array abstraction, and Reader, our byte streaming abstraction. Previously, we had a special Buf called Buf.Eof to denote the end of a byte Stream, but it occurred to us that it didn’t make sense to have this in the byte array abstraction—it made more sense to model it in the byte stream abstraction, so now the semantic lies in the Reader. Reader is experimental, and not used widely, so we didn’t bump the major version. We apologize if this causes you problems.

At long last, we’ve deprecated com.twitter.util.Bijection. This has been a long time coming, since there’s now a fully-fledged open source project built around Bijection that does everything that c.t.u.Bijection did, and a whole lot more!

New features

We’ve added several new features to Buf, our byte array abstraction. In part, this is to prepare to start exposing Netty-free interfaces, so that we can swap Netty 3 out for other backends. Some of those features are that we now have a Buf.ByteBuffer to wrap java.nio.ByteBuffer, Bufs now support reading and writing U(32|64)(BE|LE) integers with Bufs, and we’ve significantly improved the performance of concatenating Bufs, with ConcatBuf.

There are two new features on spools as we think more about object streaming. Spool now has take, useful for batching, and mapFuture, useful when you want to apply a function which returns an asynchronous result to every item in your spool.

We’ve modified the Logging trait so that it’s more extensible, making it easier to change the handlers for your logger. We hope that this will simplify having a unified way of logging across a project or organization.

Java compatibility

LoggerFactory has been hard to use from Java for a long time. We just created a LoggerFactoryBuilder, which should be much easier to use from Java. There’s an example in the LoggerFactoryBuilder compilation test. We’re excited about making Finagle easier to use from Java, so please let us know if you continue to run into trouble consuming Finagle from Java, so we can work with you to make Finagle more Java-friendly.


The Scaladocs for Flag and friends have been significantly improved. If you ever wondered how util-flags worked, the Scaladocs are now an even better place to learn the nitty gritty details.

Open source

George Leontiev singlehandedly replaced all of our old specs tests with ScalaTest ones, paving the way for Util to be published against Scala 2.11. We weren’t able to publish util against 2.11 in this most recent release, but watch this space! We’re also making big strides in 2.11-ification for Finagle, in large part inspired by George’s work.


6.19.0 2014-08-05

  • util: smattering of minor cleanups in util and finagle
  • util-core: Reader and getContent symmetry

6.18.4 2014-07-31

  • util-core: Remove confusing NOOP 0.until(5) in Future.collect().
  • util-app: Fix a bug in global flag parsing

6.18.2 2014-07-23

  • util-core: Fixes a broken sbt test
  • util-core: Log exceptions caught by ChannelStatsHandler
  • util-core: Satisfy promise on fatal exception in FuturePool task
  • util-core: small perf improvements to Future.collect, Throw, Flag
  • util-logging: Java-friendly LoggerFactory API

6.18.1 2014-07-08

  • util: Update README to reflect correct storage units.
  • util-*: Convert all tests in util to ScalaTest
  • util-app: Simplifies the logic to get the appname
  • util-io: Buf, Reader: remove Buf.Eof; end-of-stream is None
  • util-io: Create Buf.ByteBuffer to wrap java.nio.ByteBuffer

6.18.0 2014-06-23

  • util-app: Don’t kill the JVM on flag-parsing failure
  • util-app: Improve the Scaladocs for and friends
  • util-core: Add U(32|64)(BE|LE) to Buf
  • util-core: Add com.twitter.util.NilStopwatch
  • util-core: Add src/main/java dependency on src/main/scala
  • util-core: Catch InterruptedException in Closable collector thread
  • util-core: Fix MockTimer#schedule(Duration)(=> Unit)‘s cancel
  • util-core: Fix update-after-interrupt race condition in AsyncSemaphore
  • util-core: Signal the deprecation of com.twitter.util.Bijection.
  • util-logging: Add additional handlers to Logging trait

6.17.0 2014-06-04

  • util: Upgrade dependency versions
  • util-core: Scheduler productivity = cpuTime/wallTime
  • util-core: Add a take method to Spool
  • util-core: Introduce ConcatBuf
  • util-core: add Spool.collectFuture



We’ve renamed Finagle threads, so that they are now called “finagle/netty3”. This should make it easier to figure out what is going on in your stack traces.

New features

finagle-http now supports streaming the request body. This is not yet documented, but there is a pull request to add documentation to the Finagle user guide. We’d love to hear what you think.

getContent and Reader are two ways to retrieve the body of the HTTP message. The previous behavior was that when the message was chunked, calling retrieved n bytes of the message body, and getContent returned an empty ChannelBuffer. When the message was not chunked, getContent returned a ChannelBuffer filled with the message body, and calling was a future that never resolved. The new behavior is that when the message is chunked, the behavior remains the same, but when not chunked, calling retrieves n bytes of the message body. We think this is behavior is much more aligned with expectations.

The previous default for inet! resolution in Finagle was to never refresh the DNS lookup, so people had to do terrible hacks to get it to work properly. Part of the problem was that Twitter doesn’t change DNS entries frequently, so we don’t rely on DNS for service discovery often. However, the new Finagle supports timer-based DNS resolution as default in InetResolver. Thanks a ton to Alex Gleyzer, who came up with the original implementation, and Cobb, who got it ready to merge into Finagle.

Per-host stats can be too noisy to turn on in production, and will entail significant GC pressure if you have many downstream hosts. We’ve added a new flag that you can enable to turn on per host stats, com.twitter.finagle.loadbalancer.perHostStats, since they are often useful for debugging problems locally, or in staging environments.

finagle-thriftmux now supports the experimental feature GC Avoidance if you turn on the right flags. We’re beginning to load test it now, but it’s not ready for prime time yet. If you’re trying to use GC Avoidance outside of Twitter, you might have a hard time. In some parts it depends upon having a JDK which supports System.minorGc, an extra call on System which will only trigger a minor GC. We’ve discussed other ways of forcing a minor GC, like allocating a lot of big arrays very quickly, but haven’t implemented them yet. Please get in contact if you’re interested in working on this.


We’ve significantly improved the documentation around HTTP streaming, and also added a bunch of examples. This hasn’t been merged yet, but can be found at the pull request to add documentation to the Finagle user guide. We’d love to hear what you think.

New stats

We’ve added several new stats to Finagle, to generally improve insight into Finagle. We’ve added a marked_dead counter to the FailFastFactory, so that you can see when your client perceives that downstream endpoints are flapping.

We’ve also added a couple of counters in WatermarkPool, to make it easier to see when you’re having queueing problems, and are asked to wait in line for a connection, namedly pool_num_waited, and pool_num_too_many_waiters.

We’ve added a service acquisition latency stat to StatsFactoryWrapper, which gives insight into how long it takes to acquire a service. Since TCP connections are usually quite fast, and should mostly be cached, this usually measures how long you spend queueing for a connection.

Open source

Inspired in large part by the great work in Util to get ready for Scala 2.11, we’ve started making Finagle ready for Scala 2.11. A large part of this is paying down technical debt that we’ve accrued, like having half of our tests still be on specs, which is super deprecated. Because of this, we’re trying to move as much as possible onto ScalaTest, which is what we use now. Pierre-Antoine Ganaye, the author of the very cool finagle-zookeeper project, stepped up and migrated the finagle-core tests over, while getting up to speed on Finagle, and the Finagle community took on the mantle for the rest of the tests. We’re over halfway there, and we’re beginning to think about how to switch over our other projects, like Scrooge and Twitter-server.

In order to make it easier to get new contributors started with Finagle, we’ve added sections about review process and starter issues. Also, so that open source users can see how many other open source users there are and have more confidence in our commitment to open source, we’ve started an adopters list.



  • finagle: Smattering of minor cleanups in util and finagle
  • finagle: Upgrade sbt to 0.13
  • finagle: Upgrade to Netty
  • finagle-core: Add NameTree.Fail to permit failing a name without fallback
  • finagle-core: Add a generic DtabStatsFilter
  • finagle-core: Add a singleton exception and a counter in WatermarkPool
  • finagle-core: DefaultClient in terms of StackClient
  • finagle-core: Disable Netty’s thread renaming
  • finagle-core: Fix CumulativeGauge memory leak
  • finagle-core: Fix negative resolution in
  • finagle-core: Fixed ChannelStatsHandler to properly filter exceptions
  • finagle-core: Forces finagle-core to use ipv4 network stack
  • finagle-core: Improve Failure.toString
  • finagle-core: Include path and Dtab.local in NoBrokersAvailableException
  • finagle-core: Log exceptions caught by ChannelStatsHandler
  • finagle-core: Make timer-based DNS resolution as default of InetResolver
  • finagle-core: Reader and getContent symmetry
  • finagle-core: Reduces log level for common exceptions
  • finagle-core: Register clients centrally
  • finagle-doc: Add fintop to companion projects list on Finagle website
  • finagle-http: Don’t emit (illegal) newlines in lengthy dtab header values
  • finagle-http: Fix code style from an open-source contribution
  • finagle-http: Migrate from specs to ScalaTest
  • finagle-kestrel: Make transaction abort timeout configurable in MultiReader
  • finagle-mux: Added extra client logging
  • finagle-mux: Fix broken draining behavior
  • finagle-mux: Improve granularity of rate to bytes/millisecond
  • finagle-serversets: Handle errors that occur when fetching endpoints
  • finagle-serversets: Increase ZK session timeout to 10 seconds
  • finagle-serversets: Merge WeightedSocketAddresses with same host:port but different weight in Stabilizer
  • finagle-serversets: Synchronize bug fixes & test coverage across ZK facades
  • finagle-swift: Fixes pants build warning
  • finagle-thrift: Add explicit dependency on libthrift
  • finagle-thrift: Remove usage of java_sources, should be able to depend on it normally


  • finagle-core: Allow trailing semicolons in dtabs
  • finagle-core: Rescue exceptions thrown by filter in Filter.andthen(Filter)
  • finagle-core: StackClient, StackClientLike don’t leak underlying In, Out types
  • finagle-doc: Clarify cancellation
  • finagle-doc: Fix broken link in document
  • finagle-doc: Fix name footnote in finagle Names docs
  • finagle-http: Buf, Reader remove Buf.Eof; end-of-stream is None
  • finagle-http: Prepend comment to JSONP callbacks
  • finagle-http: Removing specs from the CookieMapSpec test.
  • finagle-kestrel: Make failFast configurable in Kestrel codec
  • finagle-mysql: Ensure mysql specific tracing is composed.
  • finagle-mysql: Finagle MySQL PreparedStatement accepts Value types as params.
  • finagle-serversets: Identity Providers for Serverset2
  • finagle-thriftmux: Add withProtocolFactory API endpoint
  • finagle-thriftmux: Don’t reuse InMemoryStatsReceiver in the same test


  • finagle-*: release scrooge v3.16.0
  • finagle-*: release util v6.18.0
  • finagle-core: Add description field to com.twitter.finagle.Stackable trait
  • finagle-core: Add a Flag to turn on per-host stats
  • finagle-core: Add a service acquisition latency stat to StatsFactoryWrapper
  • finagle-core: Don’t support empty path elements in com.twitter.finagle.Path
  • finagle-core: Improves FailFastFactory documentation
  • finagle-core: Make c.t.f.Failure a direct subclass of Exception
  • finagle-core: Skip SOCKS proxy when connecting to loopback address
  • finagle-core: Use Monitor from caller’s context in DefaultTimer
  • finagle-http: Add “Enhance Your Calm” and “Too Many Requests” HTTP status codes
  • finagle-http: Add exp.HttpServer, which allows request limits to be configured
  • finagle-http: Change Request#params to a memoized def
  • finagle-http: Stream request body
  • finagle-kestrel: Add Name-based methods for MultiReader construction
  • finagle-memcached: Expose the client type KetamaClient in the build() API
  • finagle-mux: GC Avoidance Algorithm
  • finagle-mux: Hook up GC avoidance to servers
  • finagle-mux: Move to the correct directory
  • finagle-serversets: Randomizes backoff interval in ZK2
  • finagle-serversets: Start resolution eagerly in ZK2
  • finagle-stats: Add a stat-filtration GlobalFlag
  • finagle-*: release ostrich v9.5.2
  • user guide: Add Google Analytics tracking code
  • user guide: Add sections about review process and starter issues
  • user guide: Update Finagle adopter list on user guide website
  • wily: Add Dtab expansion


  • finagle: Add list of Finagle adopters
  • finagle: Upgrade third-party dependencies
  • finagle-core: Add Addr.Neg to the user guide’s list of Addr types
  • finagle-core: Added Failure support for sourcing to finagle
  • finagle-core: ClientBuilder should turn per-host stats off by default (matching new Client building API).
  • finagle-core: Implement DefaultServer in terms of StackServer
  • finagle-core: Improve the Dtab API
  • finagle-core: Prevent scoping stats with the empty-string
  • finagle-core: Rolls up the /tries scope properly
  • finagle-core: ServerStatsReceiver and ClientStatsReceiver can now update their root scope
  • finagle-core: fix race case in DelayedFactory
  • finagle-core: introduce AbstractResolver
  • finagle-core: remove need for hostConnectionLimit when using ClientBuilder#stack
  • finagle-core: widen to type for ServerBuilder#stack
  • finagle-core: widen type of ClientBuilder#stack
  • finagle-doc: Removed a line from
  • finagle-http: DtabFilter should always clear dtab headers
  • finagle-http: add HOST header for CONNECT method
  • finagle-http: scala 2.10 compatible tests
  • finagle-memcached: filter out one more cancelling request exception in failure accrual
  • finagle-memcached: remove empty test
  • finagle-mux: Improve Mux server close behavior, control messages to non-Mux clients
  • finagle-mux: Marked a gc test as flaky
  • finagle-mux: Modifies MuxService to essentially be a Service[Spool[Buf], Spool[Buf]] Problem
  • finagle-mux: Rm ClientHangupException in favor of CancelledRequestException
  • finagle-mysql: Retrieving a timestamp from the DB nw creates a timestamp in UTC
  • finagle-mysql: fix for issue where time was not being returned in UTC for binary protocol
  • finagle-serversets: Prevent gauges from being garbage collected
  • finagle-thrift: Blackhole control messages sent to non-mux Thrift clients
  • finagle-thriftmux: Add per-connection protocol-usage stats
  • finagle-thriftmux: Add stats to identify ThriftMux clients and servers
  • finagle-thriftmux: Propagate Contexts from non-ThriftMux clients
  • finagle-thriftmux: add ClientBuilder#stack compatibility and make APIs symmetric
  • finagle-thriftmux: pass along ClientId with ClientBuilder API


New features

We wrote a scrooge-linter, which we’re really excited about. If you’re at a company that has a lot of Thrift IDL files, you know the pain of trying to get everyone to write them in a standard way, especially since the tooling is so anemic. scrooge-linter begins to fix that problem, by linting your IDL files so you can catch non-conforming thrift quickly and systematically.


The docs on how to use the scrooge tool from the command line have long been out of date. We just did a big refresher of them, and it’s much easier to get up and running with a new Scrooge project now.



  • scrooge-core: Add union metadata for reflection
  • scrooge-doc: Clarify docs on CLI usage
  • scrooge-generator: Fix error message for missing required field
  • scrooge-generator: Modify compiler to accept a Scaladoc comment at the end of Thrift file
  • scrooge-generator: Normalize scalatest versions between poms and 3rdparty
  • scrooge-generator: Stricter checks for invalid Thrift filenames
  • scrooge-ostrich: Default to using Protocols.binaryFactory


  • scrooge-*: release finagle 6.18.0
  • scrooge-*: release util 6.18.0
  • scrooge-linter: Fix multiple arguments to linter + pants/mvn fixes
  • scrooge: Separate flow for linter
  • scrooge: Skip includes when linting


  • scrooge-*: Upgrade dependencies to latest versions
  • scrooge: Move scrooge-linter into scrooge
  • scrooge: Add SimpleID.originalName for enum fields

Twitter Server

New features

It has historically been difficult to understand how your client is configured, even though all clients are configured very similarly, usually with only small changes in parameters. However, when debugging, users sometimes need to know how long timeouts have been set to, what kind of load balancer is being used, and other configuration parameters, so that we can debug problems more quickly. Now, we have a neat admin endpoint where users can gain insight into each client individually.

Having logging at multiple granularities is a real luxury, but sometimes you realize that you’ve set the log level incorrectly, and you need to be able to see more granular logs on a box that’s already in an interesting state, in production. To that end, we’ve added a logging handler to the Twitter-server admin service, which can both tell you about the current log levels, but can also be used to change logging granularities on the fly.

We added a new admin handler to display the base dtab, so that it’s easier to reason about what will happen to a service when it receives a new dtab. Instead of having to guess based on its behavior, or try to figure it out through inspecting the code, you can just query now, and know the right answer immediately.

Built-in metrics are one of the coolest features of Finagle, but there are really a ton of them, especially if you have many downstreams, or you use per host stats. In order to make this problem easier to deal with, we added a flag, com.twitter.finagle.stats.statsFilter, which you can pass in to filter out some stats that you know you will never use.



  • Add admin endpoint for per-client configuration
  • Add trace ID to twitter-server logging
  • Create a logging handler for on-the-fly logging updates


  • release finagle v6.18.0
  • release util v6.18.0
  • user guide: Add blurb about filtering out stats


  • Upgrade versions of all dependencies
  • Admin dtab handler: display base dtab
  • Change productivity stat to cpuTime/wallTime