[#2622] Correctly check reference count before try to work on the underlying memory

Motivation:

Because of how we use reference counting we need to check for the reference count before each operation that touches the underlying memory. This is especially true as we use sun.misc.Cleaner.clean() to release the memory ASAP when possible. Because of this the user may cause a SEGFAULT if an operation is called that tries to access the backing memory after it was released.

Modification:

Correctly check the reference count on all methods that access the underlying memory or expose it via a ByteBuffer.

Result:

Safer usage of ByteBuf
[#2623] Release local references to guard against StackOverflow in JNI

Motivation:

When we do a (env*)->GetObjectArrayElement(...) call we may created many local references which will only be cleaned up once we exist the native method. Thus a lot of memory can be used and so a StackOverFlow may be triggered. Beside this the JNI specification only say that an implementation must cope with 16 local references.

Modification:

Call (env*)->ReleaseLocalRef(...) to release the resource once not needed anymore.

Result:

Less memory usage and guard against StackOverflow
[maven-release-plugin] prepare release netty-4.0.21.Final
[maven-release-plugin] prepare for next development iteration
Correctly return from selector loop one a scheduled task is ready for processing

Motivation:

We use the nanoTime of the scheduledTasks to calculate the milli-seconds to wait for a select operation to select something. Once these elapsed we check if there was something selected or some task is ready for processing. Unfortunally we not take into account scheduled tasks here so the selection loop will continue if only scheduled tasks are ready for processing. This will delay the execution of these tasks.

Modification:

- Check if a scheduled task is ready after selecting
- also make a tiny change in NioEventLoop to not trigger a rebuild if nothing was selected because the timeout was reached a few times in a row.

Result:

Execute scheduled tasks on time.
[#2558] Define SO_REUSEPORT if not defined

Motivation:

Currently it is impossible to build netty on linux system that not define SO_REUSEPORT even if it is supported.

Modification:

Define SO_REUSEPORT if not defined.

Result:

Possible to build on more linux dists.
Fix most inspector warnings

Motivation:

It's good to minimize potentially broken windows.

Modifications:

Fix most inspector warnings from our profile
Update IntObjectHashMap

Result:

Cleaner code
Fix the build timeout when 'leak' profile is active

Motivation:

AbstractByteBufTest.testInternalBuffer() uses writeByte() operations to
populate the sample data.  Usually, this isn't a problem, but it starts
to take a lot of time when the resource leak detection level gets
higher.

In our CI machine, testInternalBuffer() takes more than 30 minutes,
causing the build timeout when the 'leak' profile is active (paranoid
level resource detection.)

Modification:

Populate the sample data using ThreadLocalRandom.nextBytes() instead of
using millions of writeByte() operations.

Result:

Test runs much faster when leak detection level is high.
Let OkResponseHandler extend SimpleChannelInboundHandler

Motivation:

OkResponseHandler is the last handler in the pipeline of the HTTP CORS
example.  It is responsible for releasing all messages it handled.

Modification:

Extend SimpleChannelInboundHandler instead of
ChannelInboundHandlerAdapter

Result:

Fixed a leak
[#2586] Use correct EventLoop to notify delayed bind failures

Motivation:

When a bind fails AbstractBootstrap will use the GlobalEventExecutor to notify the ChannelPromise. We should use the EventLoop of the Channel if possible.

Modification:

Use EventLoop of the Channel if possible to use the correct Thread to notify and so guaranteer the right order of events.

Result:

Use the correct EventLoop for notification
Log the time taken for generating the initialSeedUniquifier

- Sometimes useful to know it how long it takes from the log, to make
  sure it's not something else that is blocking.
Add missing m2eclipse life cycle mapping

Also, use ignore instead of execution because those plugins are not
really useful when building from Eclipse anyway.
Move generic code to HttpOrSpdyChooser to simplify implementations

Motivation:

HttpOrSpdyChooser can be simplified so the user not need to implement getProtocol(...) method.

Modification:

Add implementation for the method. The user can override it if necessary.

Result:

Easier usage of HttpOrSpdyChooser.
[#2644] Correctly release buffer when exception happens during send DatagramPacket or SctpMessage

Motivation:

When an exception is thrown during try to send DatagramPacket or SctpMessage a buffer may leak.

Modification:

Correctly handle allocated buffers in case of exception

Result:

No more leaks
[#2642] CompositeByteBuf.deallocate memory/GC improvement

Motivation:

CompositeByteBuf.deallocate generates unnecessary GC pressure when using the 'foreach' loop, as a 'foreach' loop creates an iterator when looping.

Modification:

Convert 'foreach' loop into regular 'for' loop.

Result:

Less GC pressure (and possibly more throughput) as the 'for' loop does not create an iterator
[#2647] Respect IOV_MAX when call writev in native transport

Motivation:

epoll transport fails on gathering write of more then 1024 buffers. As linux supports max. 1024 iov entries when calling writev(...) the epoll transport throws an exception.

Thanks again to @blucas to provide me with a reproducer and so helped me to understand what the issue is.

Modifications:

Make sure we break down the writes if to many buffers are uses for gathering writes.

Result:

Gathering writes work with any number of buffers
[#2643] Throw TooLongFrameException instead of using fireExceptionCaught

Motivation:

It's not always the case that there is another handler in the pipeline that will intercept the exceptionCaught event because sometimes users just sub-class. In this case the exception will just hit the end of the pipeline.

Modification:
Throw the TooLongFrameException so that sub-classes can handle it in the exceptionCaught(...) method directly.

Result:
Sub-classes can correctly handle the exception,
Reuse previous created HttpHeaders by HttpObjectAggregator

Motivation:

HttpObjectAggregator currently creates a new FullHttpResponse / FullHttpRequest for each message it needs to aggregate. While doing so it also creates 2 DefaultHttpHeader instances (one for the headers and one for the trailing headers). This is bad for two reasons:
  - More objects are created then needed and also populate the headers is not for free
  - Headers may get validated even if the validation was disabled in the decoder

Modification:

- Wrap the previous created HttpResponse / HttpRequest and so reuse the original HttpHeaders
- Reuse the previous created trailing HttpHeader.
- Fix a bug where the trailing HttpHeader was incorrectly mixed in the headers.

Result:

- Less GC
- Faster HttpObjectAggregator implementation
[#2650] Allow to disable http header validation in SpdyHttpDecoder and SpdyHttpCodec

Motivation:

HTTP header validation can be expensive so we should allow to disable it like we do in HttpObjectDecoder.

Modification:

Add constructor argument to disable validation.

Result:
Performance improvement
[#2651] Fix possible infinite-loop when cancel tasks

Motivations:
In our new version of HWT we used some kind of lazy cancelation of timeouts by put them back in the queue and let them pick up on the next tick. This  multiple problems:
 - we may corrupt the MpscLinkedQueue if the task is used as tombstone
 - this sometimes lead to an uncessary delay especially when someone did executed some "heavy" logic in the TimeTask

Modifications:
Use a Lock per HashedWheelBucket for save and fast removal.

Modifications:
Cancellation of tasks can be done fast and so stuff can be GC'ed and no more infinite-loop possible