fedf3ccecb
Motivation #8563 highlighted race conditions introduced by the prior optimistic update optimization in 83a19d565064ee36998eb94f946e5a4264001065. These were known at the time but considered acceptable given the perf benefit in high contention scenarios. This PR proposes a modified approach which provides roughly half the gains but stronger concurrency semantics. Race conditions still exist but their scope is narrowed to much less likely cases (releases coinciding with retain overflow), and even in those cases certain guarantees are still assured. Once release() returns true, all subsequent release/retains are guaranteed to throw, and in particular deallocate will be called at most once. Modifications - Use even numbers internally (including -ve) for live refcounts - "Final" release changes to odd number (equivalent to refcount 0) - Retain still uses faster getAndAdd, release uses CAS loop - First CAS attempt uses non-volatile read - Thread.yield() after a failed CAS provides a net gain Result More (though not completely) robust concurrency semantics for ref counting; increased latency under high contention, but still roughly twice as fast as the original logic. Bench results to follow
Netty Project
Netty is an asynchronous event-driven network application framework for rapid development of maintainable high performance protocol servers & clients.
Links
How to build
For the detailed information about building and developing Netty, please visit the developer guide. This page only gives very basic information.
You require the following to build Netty:
- Latest stable Oracle JDK 7
- Latest stable Apache Maven
- If you are on Linux, you need additional development packages installed on your system, because you'll build the native transport.
Note that this is build-time requirement. JDK 5 (for 3.x) or 6 (for 4.0+) is enough to run your Netty-based application.
Branches to look
Development of all versions takes place in each branch whose name is identical to <majorVersion>.<minorVersion>. For example, the development of 3.9 and 4.0 resides in the branch '3.9' and the branch '4.0' respectively.
Usage with JDK 9
Netty can be used in modular JDK9 applications as a collection of automatic modules. The module names follow the reverse-DNS style, and are derived from subproject names rather than root packages due to historical reasons. They are listed below:
io.netty.allio.netty.bufferio.netty.codecio.netty.codec.dnsio.netty.codec.haproxyio.netty.codec.httpio.netty.codec.http2io.netty.codec.memcacheio.netty.codec.mqttio.netty.codec.redisio.netty.codec.smtpio.netty.codec.socksio.netty.codec.stompio.netty.codec.xmlio.netty.commonio.netty.handlerio.netty.handler.proxyio.netty.resolverio.netty.resolver.dnsio.netty.transportio.netty.transport.epoll(nativeomitted - reserved keyword in Java)io.netty.transport.kqueue(nativeomitted - reserved keyword in Java)io.netty.transport.unix.common(nativeomitted - reserved keyword in Java)io.netty.transport.rxtxio.netty.transport.sctpio.netty.transport.udt
Automatic modules do not provide any means to declare dependencies, so you need to list each used module separately
in your module-info file.