sun.misc.Unsafe.getUnsafe expects a null result if the class loader is
the boot classloader and will throw a SecurityException otherwise
(whereas it should really be checking both for null and comparing
against the system classloader). However, just returning null
whenever the loader is the boot loader can cause trouble for embedded
apps which put everything in the boot loader, including application
resources.
Therefore, we only return null if it's the boot loader and we're being
called from Unsafe.getUnsafe.
As described in readme.txt, a standalone OpenJDK build embeds all
libraries, classes, and other files needed at runtime in the resulting
binary, eliminating dependencies on external resources.
We now consult the JAVA_HOME environment variable to determine where
to find the system library JARs and SOs. Ultimately, we'll want to
support self-contained build, but this allows Avian to behave like a
conventional libjvm.so.
The main changes in this commit ensure that we don't hold the global
class lock when doing class resolution using application-defined
classloaders. Such classloaders may do their own locking (in fact,
it's almost certain), making deadlock likely when mixed with VM-level
locking in various orders.
Other changes include a fix to avoid overflow when waiting for
extremely long intervals and a GC root stack mapping bug.
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.
Whereas the GNU Classpath port used the strategy of patching Classpath
with core classes from Avian so as to minimize changes to the VM, this
port uses the opposite strategy: abstract and isolate
classpath-specific features in the VM similar to how we abstract away
platform-specific features in system.h. This allows us to use an
unmodified copy of OpenJDK's class library, including its core classes
and augmented by a few VM-specific classes in the "avian" package.
