This is the simplest possible ConcurrentHashMap I could come up with
that works and is actually concurrent in the way one would expect.
It's pretty unconventional, being based on a persistent red-black
tree, and not particularly memory-efficient or cache-friendly. I
think this is a good place to start, though, and it should perform
reasonably well for most workloads. Patches for a more efficient
implementation are welcome!
I also implemented AtomicReferenceArray, since I was using it in my
first, naive attempt to implement ConcurrentHashMap.
I had to do a bit of refactoring, including moving some non-standard
stuff from java.util.Collections to avian.Data so I could make it
available to code outside the java.util package, which is why I had to
modify several unrelated files.
This makes them available in all class libraries, not just the OpenJDK
library. Note that I've also removed the unecessary idle statements,
per ab4adef.
The former just defers to the latter for now, since it provides
strictly weaker guarantees. Thus it's correct to use full
volatile-style barriers, though not as efficient as it could be on
some architectures.
Unsafe.compareAndSwapLong was moved from classpath-openjdk.cpp to
builtin.cpp, but the fieldForOffset helper function was not, which
only caused problems when I tried to build for ARM. This commit moves
said helper function, along with Unsafe.getVolatileLong, which also
uses it.
The intent of this target is to run our test suite against the installed jre.
This should help prevent our VM from diverging in implementation from the jdk.
The remainder of this commit fixes the problems that this exposes.
Previously, I used a shell script to extract modification date ranges
from the Git history, but that was complicated and unreliable, so now
every file just gets the same year range in its copyright header. If
someone needs to know when a specific file was modified and by whom,
they can look at the Git history themselves; no need to include it
redundantly in the header.
This mainly moves several sun.misc.Unsafe method implementations from
classpath-openjdk.cpp to builtin.cpp so that the Avian and Android
builds can use them.
It also replaces FinalizerReference.finalizeAllEnqueued with a no-op,
since the real implementations assumes too much about how the VM
handles (or delegates) finalization.
OpenJDK uses an alternative to Object.finalize for resource cleanup in
the form of sun.misc.Cleaner. Normally, OpenJDK's
java.lang.ref.Reference.ReferenceHandler thread handles this, calling
Cleaner.clean on any instances it finds in its "pending" queue.
However, Avian handles reference queuing internally, so it never
actually adds anything to that queue, so the VM must call
Cleaner.clean itself.
The biggest change in this commit is to split the system classloader
into two: one for boot classes (e.g. java.lang.*) and another for
application classes. This is necessary to make OpenJDK's security
checks happy.
The rest of the changes include bugfixes and additional JVM method
implementations in classpath-openjdk.cpp.
