Motivation:
We have found out that ByteBufUtil.indexOf can be inefficient for substring search on
ByteBuf, both in terms of algorithm complexity (worst case O(needle.readableBytes *
haystack.readableBytes)), and in constant factor (esp. on Composite buffers).
With implementation of more performant search algorithms we have seen improvements on
the order of magnitude.
Modifications:
This change introduces three search algorithms:
1. Knuth Morris Pratt - classical textbook algorithm, a good default choice.
2. Bit mask based algorithm - stable performance on any input, but limited to maximum
search substring (the needle) length of 64 bytes.
3. Aho–Corasick - worse performance and higher memory consumption than [1] and [2], but
it supports multiple substring (the needles) search simultaneously, by inspecting every
byte of the haystack only once.
Each algorithm processes every byte of underlying buffer only once, they are implemented
as ByteProcessor.
Result:
Efficient search algorithms with linear time complexity available in Netty (I will share
benchmark results in a comment on a PR).
Motivation:
PoolChunk requires a link to a PoolThreadCache to init ByteBuf. Currently the link is retrieved from a thread local: arena.parent.threadCache().
It has some performance cost. At the beginning of the allocation call the PoolThreadCache is already retrieved from the thread local. The reference can be propagated through the calls and used.
Modifications:
Replace second lookup of PoolThreadCache during ByteBuf init by propagation of a reference to PoolThreadCache down in the allocation stack explicitly
Result:
Improve performance of ByteBuf allocation
--Before--
Benchmark (size) (tokens) (useThreadCache) Mode Cnt Score Error Units
SimpleByteBufPooledAllocatorBenchmark.getAndRelease 123 0 true avgt 20 57.112 ± 1.004 ns/op
SimpleByteBufPooledAllocatorBenchmark.getAndRelease 123 100 true avgt 20 222.827 ± 1.307 ns/op
--After--
Benchmark (size) (tokens) (useThreadCache) Mode Cnt Score Error Units
SimpleByteBufPooledAllocatorBenchmark.getAndRelease 123 0 true avgt 20 50.732 ± 1.321 ns/op
SimpleByteBufPooledAllocatorBenchmark.getAndRelease 123 100 true avgt 20 216.892 ± 3.806 ns/op
Motivation:
PoolChunk.usage() method has non-trivial computations. It is used currently in hot path methods invoked when an allocation and de-allocation are happened.
The idea is to replace usage() output comparison against percent thresholds by Chunk.freeBytes plain comparison against absolute thresholds. In such way the majority of computations from the threshold conditions are moved to init logic.
Modifications:
Replace PoolChunk.usage() conditions in PoolChunkList with equivalent conditions for PoolChunk.freeBytes()
Result:
Improve performance of allocation and de-allocation of ByteBuf from normal size cache pool
Motivation:
The current implementation of log2 in PoolThreadCache uses a loop and less efficient than an version based on Integer.numberOfLeadingZeros (intrinsic).
Modifications:
Replace the current log2 implementation in PoolThreadCache with a version based on Integer.numberOfLeadingZeros
Result:
It can improve performance slightly during allocation and de-allocation of ByteBuf using pooled allocator.
Motivation:
FixedCompositeByteBuf.isDirect() should return the same value as EMPTY_BUFFER.isDirect() when constructed via an empty array
Modifications:
- Return correct value when constructed via empty array.
- Add unit test
Result:
FixedCompositeByteBuf.isDirect() returns correct value
Motivation:
We hat a typo in the property name that is used in PooledByteBufAllocator.
Modifications:
Change from "...allocation.." to "...allocator.."
Result:
More consistent property naming
Motivation
Recent optimization #9765 introduced a bug where the native indices of
the internal reused duplicate nio buffer are not properly reset prior to
using it to copy data during a reallocation operation. This can result
in BufferOverflowExceptions thrown during ByteBuf capacity changes.
The code path in question applies only to pooled direct buffers when
Unsafe is disabled or not available.
Modification
Ensure ByteBuffer#clear() is always called on the reused internal nio
buffer prior to returning it from PooledByteBuf#internalNioBuffer()
(protected method); add unit test that exposes the bug.
Result
Fixes#9911
# Motivation:
`DefaultByteBufHolder.equals()` considers another object equal if it's an instance of `ByteBufferHolder` and if the contents of two objects are equal. However, the behavior of `equals` method is not a part of the `ByteBufHolder` contract so `DefaultByteBufHolder`'s version may be causing violation of the symmetric property if other classes have different logic.
There are already a few classes that are affected by this: `DefaultHttp2GoAwayFrame`, `DefaultHttp2UnknownFrame`, and `SctpMessage` are all overriding `equals` method breaking the symmetric property.
Another effect of this behavior is that all instances with empty data are considered equal. That may not be desireable in the situations when instances are created for predefined constants, e.g. `FullBulkStringRedisMessage.NULL_INSTANCE` and `FullBulkStringRedisMessage.EMPTY_INSTANCE` in `codec-redis`.
# Modification:
Make `DefaultByteBufHolder.equals()` implementation only work for the objects of the same class.
# Result:
- The symmetric property of the `equals` method is restored for the classes in question.
- Instances of different classes are not considered equal even if the content of the data they hold are the same.
Motivation:
We should use Objects.requireNonNull(...) as we require java8
Modifications:
Replace ObjectUtil.checkNonNull(...) with Objects.requireNonNull(...)
Result:
Code cleanup
Motivation
While working on other changes I noticed some opportunities to
streamline a few things in AbstractByteBuf.
Modifications
- Avoid duplicate ensureAccessible() checks in discard(Some)ReadBytes()
and ensureWritable0(int) methods
- Simplify ensureWritable0(int) logic
- Make some conditional checks more concise
Result
Cleaner, possibly faster code
Motivation:
Currently when use of Unsafe is disabled and an internal reallocation is
performed for a direct PooledByteBuf, a one-off temporary duplicate is
made of the source and destination backing nio buffers so that the
copy can be done in a threadsafe manner.
The need for this can be reduced by sharing the temporary duplicate
buffer that is already stored in the corresponding destination
PooledByteBuf instance.
Modifications:
Have PoolArena#memoryCopy(...) take the destination PooledByteBuf
instead of the underlying mem reference and offset, and use
internalNioBuffer() to obtain/initialize a reusable duplicate of the
backing nio buffer.
Result:
Fewer temporary allocations when resizing direct pooled ByteBufs in the
non-Unsafe case
Motivation
There's currently no way to determine whether an arbitrary ByteBuf
behaves internally like a "singluar" buffer or a composite one, and this
can be important to know when making decisions about how to manipulate
it in an efficient way.
An example of this is the ByteBuf#discardReadBytes() method which
increases the writable bytes for a contiguous buffer (by readerIndex)
but does not for a composite one.
Unfortunately !(buf instanceof CompositeByteBuf) is not reliable, since
for example this will be true in the case of a sliced CompositeByteBuf
or some third-party composite implementation.
isContiguous was chosen over isComposite since we want to assume "not
contiguous" in the unknown/default case - the doc will it clear that
false does not imply composite.
Modifications
- Add ByteBuf#isContiguous() which returns true by default
- Override the "concrete" ByteBuf impls to return true and ensure
wrapped/derived impls delegate it appropriately
- Include some basic unit tests
Result
Better assumptions/decisions possible when manipulating arbitrary
ByteBufs, for example when combining/cumulating them.
Motivation:
At the moment we directly extend the Recycler base class in our code which makes it hard to experiment with different Object pool implementation. It would be nice to be able to switch from one to another by using a system property in the future. This would also allow to more easily test things like https://github.com/netty/netty/pull/8052.
Modifications:
- Introduce ObjectPool class with static method that we now use internally to obtain an ObjectPool implementation.
- Wrap the Recycler into an ObjectPool and return it for now
Result:
Preparation for different ObjectPool implementations
Motivation
Currently doc != code and so one needs to change. Though behaviour as
currently documented might be more intuitive, we don't want to break
anyone so will adjust the doc instead. See #9503 for discussion.
Modifications
Correct the javadoc of indexOf(...) method in ByteBuf abstract class.
Results
Correct javadoc
Motivation
This is a "simpler" alternative to #9416 which fixes the same
CompositeByteBuf bugs described there, originally reported by @jingene
in #9398.
Modifications
- Add fields to Component class for the original buffer along with its
adjustment, which may be different to the already-stored unwrapped
buffer. Use it in appropriate places to ensure correctness and
equivalent behaviour to that prior to the earlier optimizations
- Add comments explaining purpose of each of the Component fields
- Unwrap more kinds of buffers in newComponent method to extend scope of
the existing indirection-reduction optimization
- De-duplicate common buffer consolidation logic
- Unit test for the original bug provided by @jingene
Result
- Correct behaviour / fixed bugs
- Some code deduplication / simplification
- Unwrapping optimization applied to more types of buffers
The downside is increased mem footprint from the two new fields, and
additional allocations in some specific cases, though those should be
rare.
Co-authored-by: jingene <jingene0206@gmail.com>
Motivation:
The Netty classes are initialized at build time by default for GraalVM Native Image compilation. This is configured via the `--initialize-at-build-time=io.netty` option. While this reduces start-up time it can lead to some problems:
- The class initializer of `io.netty.buffer.PooledByteBufAllocator` looks at the maximum memory size to compute the size of internal buffers. If the class initializer runs during image generation, then the buffers are sized according to the very large heap size that the image generator uses, and Netty allocates several arrays that are 16 MByte. The fix is to initialize the following 3 classes at run time: `io.netty.buffer.PooledByteBufAllocator,io.netty.buffer.ByteBufAllocator,io.netty.buffer.ByteBufUtil`. This fix was dependent on a GraalVM Native Image fix that was included in 19.2.0.
- The class initializer of `io.netty.handler.ssl.util.ThreadLocalInsecureRandom` needs to be initialized at runtime to ensure that the generated values are trully random and not fixed for each generated image.
- The class initializers of `io.netty.buffer.AbstractReferenceCountedByteBuf` and `io.netty.util.AbstractReferenceCounted` compute field offsets. While the field offset recomputation is necessary for correct execution as a native image these initializers also have logic that depends on the presence/absence of `sun.misc.Unsafe`, e.g., via the `-Dio.netty.noUnsafe=true` flag. The fix is to push these initializers to runtime so that the field offset lookups (and the logic depending on them) run at run time. This way no manual substitutions are necessary either.
Modifications:
Add `META-INF/native-image` configuration files that correctly trigger the inialization of the above classes at run time via `--initialize-at-run-time=...` flags.
Result:
Fixes the initialisation issues described above for Netty executables built with GraalVM.
Motivation:
AbstractByteBuf.indexOf(...) currently delegates to ByteBufUtils.indexOf(...) which will create a new ByteBufProcessor on each call. This is done to reduce overhead of bounds-checks. Unfortunally while this reduces bounds checks it produces a lot of GC. We can just implement our own version in AbstractByteBuf which makes use of _getByte(...) and so does no bound checks as well but also not need to create any garbage.
Modifications:
Write optimized implementation of indexOf(...) for AbstractByteBuf
Result:
Fixes https://github.com/netty/netty/issues/9499.
Motivation:
If all we need is the FileChannel we should better use RandomAccessFile as FileInputStream and FileOutputStream use a finalizer.
Modifications:
Replace FileInputStream and FileOutputStream with RandomAccessFile when possible.
Result:
Fixes https://github.com/netty/netty/issues/8078.
Motivation
region is preserved when capacity is increased, not just the readable
part. The behaviour is still different however when the capacity is
_decreased_ - data outside the currently-readable region is zeroed.
Modifications
Update ByteBuf capacity(int) implementations to also copy the whole
buffer region when the new capacity is less than the current capacity.
Result
Consistent behaviour of ByteBuf#capacity(int) regardless of whether the
new capacity is greater than or less than the current capacity.
Motivation
Underlying array allocations in UnpooledHeapByteBuf are intended be done
via the protected allocateArray(int) method, so that they can be tracked
and/or overridden by subclasses, for example
UnpooledByteBufAllocator$InstrumentedUnpooledHeapByteBuf or #8015. But
it looks like an explicit allocation was missed in the copy(int,int)
method.
Modification
Just use alloc().heapBuffer(...) for the allocation
Result
No possibility of "missing" array allocations when ByteBuf#copy is used.
Motivation:
#9224 introduced overrides of ByteBufUtil#writeUtf8(...) and related
methods to operate on a sub-CharSequence directly to save having to
allocate substrings, but it missed an edge case where the subsequence
does not extend to the end of the CharSequence and the last char in the
sequence is a high surrogate.
Due to the catch-IndexOutOfBoundsException optimization that avoids an
additional bounds check, it would be possible to read past the specified
end char index and successfully decode a surrogate pair which would
otherwise result in a '?' byte being written.
Modifications:
- Check for end-of-subsequence before reading next char after a high
surrogate is encountered in the
writeUtf8(AbstractByteBuf,int,CharSequence,int,int) and
utf8BytesNonAscii methods
- Add unit test for this edge case
Result:
Bug is fixed.
This removes the bounds-check-avoidance optimization but it does not
appear to have a measurable impact on benchmark results, including when
the char sequence contains many surrogate pairs (which should be rare in
any case).
* Correctly take length of ByteBufInputStream into account for readLine() / readByte()
Motivation:
ByteBufInputStream did not correctly take the length into account when validate bounds for readLine() / readByte() which could lead to read more then allowed.
Modifications:
- Correctly take length into account
- Add unit tests
- Fix existing unit test
Result:
Correctly take length of ByteBufInputStream into account.
Related to https://github.com/netty/netty/pull/9306.
Motivation:
buffer.isReadable() should not be used to limit the amount of data that can be read as the amount may be less then was is readable.
Modification:
- Use available() which takes the length into account
- Add unit test
Result:
Fixes https://github.com/netty/netty/issues/9305
Motivation:
Fix the issue of incorrectly calculating the number of dump rows when using prettyHexDumpmethod in ByteBufUtil. The way to find the remainder is either length % 16 or length & 15
Modification:
Fixed the way to calculate the remainder
Result:
Fixed#9301
Motivation:
Some methods that either override others or are implemented as part of implementation an interface did miss the `@Override` annotation
Modifications:
Add missing `@Override`s
Result:
Code cleanup
Motivation:
At the moment EmptyByteBuf.getCharSequence(0,...) will return null while it must return a "".
Modifications:
- Let EmptyByteBuf.getCharSequence(0,...) return ""
- Add unit test
Result:
Fixes https://github.com/netty/netty/issues/9271.
Motivation
It would be useful to be able to write UTF-8 encoded subsequence of
CharSequence characters to a ByteBuf without needing to create a
temporary object via CharSequence#subSequence().
Modification
Add overloads of ByteBufUtil writeUtf8, reserveAndWriteUtf8 and
utf8Bytes methods which take explicit subsequence bounds.
Result
More efficient writing of substrings to byte buffers possible
Motivation
There's quite a lot of duplicate/equivalent logic across the various
concrete ByteBuf implementations. We could take this even further but
for now I've focused on the PooledByteBuf sub-hierarchy.
Modifications
- Move common logic/methods into existing PooledByteBuf abstract
superclass
- Shorten PooledByteBuf.capacity(int) method implementation
Result
Less code to maintain
Motivation
While digging around looking at something else I noticed that these
share a lot of logic and it would be nice to reduce that duplication.
Modifications
Have UnpooledUnsafeDirectByteBuf extend UnpooledDirectByteBuf and make
adjustments to ensure existing behaviour remains unchanged.
The most significant addition needed to UnpooledUnsafeDirectByteBuf was
re-overriding the getPrimitive/setPrimitive methods to revert back to
the AbstractByteBuf versions which include bounds checks
(UnpooledDirectByteBuf excludes these as an optimization, relying on
those done by underlying ByteBuffer).
Result
~200 fewer lines, less duplicate logic.
Motivation:
1. Users will be able to use an optimized version of
`UnpooledHeapByteBuf` and override behavior of methods if required.
2. Consistency with `UnpooledDirectByteBuf`, `UnpooledHeapByteBuf`, and
`UnpooledUnsafeDirectByteBuf`.
Modifications:
- Add `public` access modifier to `UnpooledUnsafeHeapByteBuf` class and
ctor;
Result:
Public access for optimized version of `UnpooledHeapByteBuf`.
Motivation
There are a few minor inconsistencies / redundant operations in the
ByteBuf implementations which would be good to fix.
Modifications
- Unnecessary ByteBuffer.duplicate() performed in
CompositeByteBuf.nioBuffer(int,int)
- Add missing checkIndex(...) check to
ReadOnlyByteBufferBuf.nioBuffer(int,int)
- Remove duplicate bounds check in
ReadOnlyByteBufferBuf.getBytes(int,byte[],int,int)
- Omit redundant bounds check in
UnpooledHeapByteBuf.getBytes(int,ByteBuffer)
Result
More consistency and slightly less overhead
Motivation
ByteBuf capacity is automatically increased as needed up to maxCapacity
when writing beyond the buffer's current capacity. However there's no
way to tell in general whether such an increase will result in a
relatively costly internal buffer re-allocation.
For unpooled buffers it always does, in pooled cases it depends on the
size of the associated chunk of allocated memory, which I don't think is
currently exposed in any way.
It would sometimes be useful to know where this limit is when making
external decisions about whether to reuse or preemptively reallocate.
It would also be advantageous to take this limit into account when
auto-increasing the capacity during writes, to defer such reallocation
until really necessary.
Modifications
Introduce new AbstractByteBuf.maxFastWritableBytes() method which will
return a value >= writableBytes() and <= maxWritableBytes().
Make use of the new method in the sizing decision made by the
AbstractByteBuf.ensureWritable(...) methods.
Result
Less reallocation/copying.
Motivation
A small thread-safety bug was introduced during the internal
optimizations of ComponentByteBuf made a while back in #8437. When there
is a single component which was added as a slice,
internalNioBuffer(int,int) will currently return the unwrapped slice's
un-duplicated internal NIO buffer. This is not safe since it could be
modified concurrently with other usage of that parent buffer.
Modifications
Delegate internalNioBuffer to nioBuffer in this case, which returns a
duplicate. This matches what's done in derived buffers in general
(for the same reason). Add unit test.
Result
Fixed possible thread-safety bug
Motivation
Direct buffers are normally preferred when interfacing with raw
sockets. Currently netty will only return direct io buffers (for reading
from a channel) when a platform has unsafe. However, this is
inconsistent with the write-side (filterOutboundMessage) where a direct
byte buffer will be returned if pooling is enabled. This means that
environments without unsafe (and no manual netty configurations) end up
with many pooled heap byte buffers for reading, many pooled direct byte
buffers for writing, and jdk pooled byte buffers (for reading).
Modifications
This commit modifies the AbstractByteBufAllocator to return a direct
byte buffer for io handling when the platform has unsafe or direct byte
buffers are pooled.
Result:
Use direct buffers when direct buffers are pooled for IO.
* Fix incorrect behavior of ReadOnlyByteBufferBuf.getBytes(int,ByteBuffer)
Motivation
It currently will succeed when the destination is larger than the source
range, but the ByteBuf javadoc states this should be a failure, as is
the case with all the other implementations.
Modifications
- Fix logic to fail the bounds check in this case
- Remove explicit null check which isn't done in any equivalent method
- Add unit test
Result
More correct/consistent behaviour
Motivation:
1f93bd3 introduced a regression that could lead to not have the lastAccessed field correctly null'ed out when the endOffset of the internal Component == CompositeByteBuf.readerIndex()
Modifications:
- Correctly null out the lastAccessed field in any case
- Add unit tests
Result:
Fixes regression in CompositeByteBuf.discard*ReadBytes()
Motivation
AbstractReferenceCounted and AbstractReferenceCountedByteBuf contain
duplicate logic for managing the volatile refcount in an optimized and
consistent manner, which increased in complexity in #8583. It's possible
to extract this into a common helper class now that all access is via an
AtomicIntegerFieldUpdater.
Modifications
- Move duplicate logic into a shared ReferenceCountUpdater class
- Incorporate some additional simplification for the most common single
increment/decrement cases (fewer checks/operations)
Result
Less code duplication, better encapsulation of the "non-trivial"
internal volatile refcount manipulation
Motivation:
The CompositeByteBuf discardReadBytes / discardReadComponents methods are currently quite inefficient, including when there are no read components to discard. We would like to call the latter more frequently in ByteToMessageDecoder#COMPOSITE_CUMULATOR.
In the same context it would be beneficial to perform a "shallow copy" of a composite buffer (for example when it has a refcount > 1) to avoid having to allocate and copy the contained bytes just to obtain an "independent" cumulation.
Modifications:
- Optimize discardReadBytes() and discardReadComponents() implementations (start at first comp rather than performing a binary search for the readerIndex).
- New addFlattenedComponents(boolean,ByteBuf) method which performs a shallow copy if the provided buffer is also composite and avoids adding any empty buffers, plus unit test.
- Other minor optimizations to avoid unnecessary checks.
Results:
discardReadXX methods are faster, composite buffers can be easily appended without deepening the buffer "tree" or retaining unused components.
Motivation:
We synchronize on the chunk.arena when produce the String returned by PoolSubpage.toString() which may raise a NPE when chunk == null. Chunk == null for the head of the linked-list and so a NPE may raised by a debugger. This NPE can never happen in real code tho as we never access toString() of the head.
Modifications:
Add null checks and so fix the possible NPE
Result:
No NPE when using a debugger and inspect the PooledByteBufAllocator.
Motivation:
We currently use a thread local cache for all threads which often is suprising to users as it may result in a lot of memory usage if they allocate buffers from outside the EventLoop in different threads. We should better not do this by default to keep suprises to a minimum. Users that need the performance and know what they are doing can still change this.
Modifications:
Change io.netty.allocator.useCacheForAllThreads to false by default
Result:
Related to https://github.com/netty/netty/issues/8536.
Motivation:
In MemoryRegionCache.Entry we use the Recycler to reduce GC pressure and churn. The problem is that these will also be recycled when the PoolThreadCache is collected and finalize() is called. This then can have the effect that we try to load class but the WebApp is already stoped.
This will produce an stacktrace like this on Tomcat:
```
19-Mar-2019 15:53:21.351 INFO [Finalizer] org.apache.catalina.loader.WebappClassLoaderBase.checkStateForResourceLoading Illegal access: this web application instance has been stopped already. Could not load [java.util.WeakHashMap]. The following stack trace is thrown for debugging purposes as well as to attempt to terminate the thread which caused the illegal access.
java.lang.IllegalStateException: Illegal access: this web application instance has been stopped already. Could not load [java.util.WeakHashMap]. The following stack trace is thrown for debugging purposes as well as to attempt to terminate the thread which caused the illegal access.
at org.apache.catalina.loader.WebappClassLoaderBase.checkStateForResourceLoading(WebappClassLoaderBase.java:1383)
at org.apache.catalina.loader.WebappClassLoaderBase.checkStateForClassLoading(WebappClassLoaderBase.java:1371)
at org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1224)
at org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1186)
at io.netty.util.Recycler$3.initialValue(Recycler.java:233)
at io.netty.util.Recycler$3.initialValue(Recycler.java:230)
at io.netty.util.concurrent.FastThreadLocal.initialize(FastThreadLocal.java:188)
at io.netty.util.concurrent.FastThreadLocal.get(FastThreadLocal.java:142)
at io.netty.util.Recycler$Stack.pushLater(Recycler.java:624)
at io.netty.util.Recycler$Stack.push(Recycler.java:597)
at io.netty.util.Recycler$DefaultHandle.recycle(Recycler.java:225)
at io.netty.buffer.PoolThreadCache$MemoryRegionCache$Entry.recycle(PoolThreadCache.java:478)
at io.netty.buffer.PoolThreadCache$MemoryRegionCache.freeEntry(PoolThreadCache.java:459)
at io.netty.buffer.PoolThreadCache$MemoryRegionCache.free(PoolThreadCache.java:430)
at io.netty.buffer.PoolThreadCache$MemoryRegionCache.free(PoolThreadCache.java:422)
at io.netty.buffer.PoolThreadCache.free(PoolThreadCache.java:279)
at io.netty.buffer.PoolThreadCache.free(PoolThreadCache.java:270)
at io.netty.buffer.PoolThreadCache.free(PoolThreadCache.java:241)
at io.netty.buffer.PoolThreadCache.finalize(PoolThreadCache.java:230)
at java.lang.System$2.invokeFinalize(System.java:1270)
at java.lang.ref.Finalizer.runFinalizer(Finalizer.java:102)
at java.lang.ref.Finalizer.access$100(Finalizer.java:34)
at java.lang.ref.Finalizer$FinalizerThread.run(Finalizer.java:217)
```
Beside this we also need to ensure we not try to lazy load SizeClass when the finalizer is used as it may not be present anymore if the ClassLoader is already destroyed.
This would produce an error like:
```
20-Mar-2019 11:26:35.254 INFO [Finalizer] org.apache.catalina.loader.WebappClassLoaderBase.checkStateForResourceLoading Illegal access: this web application instance has been stopped already. Could not load [io.netty.buffer.PoolArena$1]. The following stack trace is thrown for debugging purposes as well as to attempt to terminate the thread which caused the illegal access.
java.lang.IllegalStateException: Illegal access: this web application instance has been stopped already. Could not load [io.netty.buffer.PoolArena$1]. The following stack trace is thrown for debugging purposes as well as to attempt to terminate the thread which caused the illegal access.
at org.apache.catalina.loader.WebappClassLoaderBase.checkStateForResourceLoading(WebappClassLoaderBase.java:1383)
at org.apache.catalina.loader.WebappClassLoaderBase.checkStateForClassLoading(WebappClassLoaderBase.java:1371)
at org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1224)
at org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1186)
at io.netty.buffer.PoolArena.freeChunk(PoolArena.java:287)
at io.netty.buffer.PoolThreadCache$MemoryRegionCache.freeEntry(PoolThreadCache.java:464)
at io.netty.buffer.PoolThreadCache$MemoryRegionCache.free(PoolThreadCache.java:429)
at io.netty.buffer.PoolThreadCache$MemoryRegionCache.free(PoolThreadCache.java:421)
at io.netty.buffer.PoolThreadCache.free(PoolThreadCache.java:278)
at io.netty.buffer.PoolThreadCache.free(PoolThreadCache.java:269)
at io.netty.buffer.PoolThreadCache.free(PoolThreadCache.java:240)
at io.netty.buffer.PoolThreadCache.finalize(PoolThreadCache.java:229)
at java.lang.System$2.invokeFinalize(System.java:1270)
at java.lang.ref.Finalizer.runFinalizer(Finalizer.java:102)
at java.lang.ref.Finalizer.access$100(Finalizer.java:34)
at java.lang.ref.Finalizer$FinalizerThread.run(Finalizer.java:217)
```
Modifications:
- Only try to put the Entry back into the Recycler if the PoolThredCache is not destroyed because of the finalizer.
- Only try to access SizeClass if not triggered by finalizer.
Result:
No IllegalStateException anymoe when a webapp is reloaded in Tomcat that uses netty and uses the PooledByteBufAllocator.
Motivation:
The special case fixed in #8497 also requires that we keep a derived slice when trimming components in place, as done by the capacity(int) and discardReadBytes() methods.
Modifications:
Ensure that we keep a ref to trimmed components' original retained slice in capacity(int) and discardReadBytes() methods, so that it is released properly when the they are later freed. Add unit test which fails prior to the fix.
Result:
Edge case leak is eliminated.
Motivation:
PooledByteBufAllocator uses a PoolThreadCache per Thread that allocates / deallocates to minimize the performance overhead. This PoolThreadCache is trimmed after X allocations to free up buffers that are not allocated for a long time. This works out quite well when the app continues to allocate but fails if the app stops to allocate frequently (for whatever reason) and so a lot of memory is wasted and not given back to the arena / freed.
Modifications:
- Add a ThreadExecutorMap that offers multiple methods that wrap Runnable / ThreadFactory / Executor and allow to call ThreadExecutorMap.currentEventExecutor() to get the current executing EventExecutor for the calling Thread.
- Use these methods in the constructors of our EventExecutor implementations (which also covers the EventLoop implementations)
- Add io.netty.allocator.cacheTrimIntervalMillis system property which can be used to specify a fixed rate / interval on which we should try to trim the PoolThreadCache for a EventExecutor that allocates.
- Add PooledByteBufAllocator.trimCurrentThreadCache() to allow the user to trim the cache of the calling thread manually.
- Add testcases
- Introduce FastThreadLocal.getIfExists()
Result:
Allow to better / more frequently trim PoolThreadCache and so give back memory to the area / system.
Motivation:
We should run a CI job using J9 to ensure netty also works when using different JVMs.
Modifications:
- Adjust PooledByteBufAllocatorTest to be able to complete faster when using a JVM which takes longer when joining Threads (this seems to be the case with J9).
Result:
Be able to run CI against J9.
Motivation:
We can remove some properties for which we introduced replacements.
Modifications:
io.netty.buffer.bytebuf.checkAccessible, io.netty.leakDetectionLevel, org.jboss.netty.tryUnsafe properties removed
Result:
Code cleanup
Motivation:
We can just use Objects.requireNonNull(...) as a replacement for ObjectUtil.checkNotNull(....)
Modifications:
- Use Objects.requireNonNull(...)
Result:
Less code to maintain.
