Another update:
http://cr.openjdk.java.net/~mcimadamore/panama/8234049_v3/
And a delta of the changes since last version (v2) here:
http://cr.openjdk.java.net/~mcimadamore/panama/8234049_v3_delta/
The javadoc has been updated inline here:
http://cr.openjdk.java.net/~mcimadamore/panama/memaccess_javadoc/jdk/incubator/foreign/package-summary.html
Summary of changes:
* fixed some (cosmetic) issues in FileChannelmpl following offline
discussion with Alan
* changed tests group definition, so that now jdk_foreign is part of
tier1_part3
* updated javadoc in various places to fix code samples (as per Paul
comments)
* updated javadoc in MemoryHandles to talk about access modes (as per
Paul comments) - I added a new section on top, and then referred to in
from all relevant places
* some changes to use Objects.hash (as per Paul comments), and some
minor refactor in the AddreddGenerator (to use switch expression)
* tightened javadoc for MemoryAddress::copy - the method now is
specified to throw IAE if the range of source/dest addresses overlap -
I've fixed the impl and added a test (as per Raffaello comments)
* tightened byte buffer VarHandle view - if the view is created from a
byte buffer obtained from a segment (!!!) we should do a segment check -
added tests
And here's a list of the pending API-related issues. Since these are
IMHO minor issues, I suggest we defer them to a followup minor cleanup,
so that we can move ahead with finalization of the CSR with the current
API. Here's the list:
* Should MemoryAddress implement Comparable? I think the answer is
"probably not" - an address doesn't have a 'length' so you can't really
do a range comparison (maybe memory segments though?). For now, users
can project to byte buffer and take it from there (since ByteBuffer <:
Comparable)
* should we have a way to ask a Layout if its size is specified ? (Paul)
* MemoryAddress::offset() vs. MemoryAddress::offset(long) -- not much
distance between these two semantically different operations (Paul
suggested using 'add' - which I'm not enthusiastic about because it's
not adding two addresses - it's adding a long to an address...)
* MemorySegment::isAccessible() -- as the A* word is overloaded, some
other name should be found?
* MemorySegment::acquire() -- replace with MemorySegment::fork?
Thanks
Maurizio
On 06/12/2019 10:43, Maurizio Cimadamore wrote:
Hi,
here's an updated version of the patch:
http://cr.openjdk.java.net/~mcimadamore/panama/8234049_v2/
And a delta of the changes since last version here:
http://cr.openjdk.java.net/~mcimadamore/panama/8234049_v2_delta/
The javadoc has been updated inline here:
http://cr.openjdk.java.net/~mcimadamore/panama/memaccess_javadoc/jdk/incubator/foreign/package-summary.html
Summary of changes:
* fixed spurious protected methods in AbstractLayout and subclasses
which leaked into API
* removed library_call.cpp changes, as these are being tracked
separately by Vlad
* compacted ILOAD code in AddressVarHandleGenerator
* replaced uses of ++i/--i with i + 1/i - 1 in MemoryScope
I have made no changes to the *name* of the methods in the API. In
fact, I suggest we keep a list of the names we'd like to revisit, and
we address them all at once at the end of the review (once we're happy
with the contents). Here's a list of the current open naming issues:
* MemoryAddress::offset() vs. MemoryAddress::offset(long) -- not much
distance between these two semantically different operations
* MemorySegment::isAccessible() -- as the A* word is overloaded, some
other name should be found?
* MemorySegment::acquire() -- replace with MemorySegment::fork?
Cheers
Maurizio
On 05/12/2019 21:04, Maurizio Cimadamore wrote:
Hi,
as part of the effort to upstream the changes related to JEP 370
(foreign memory access API) [1], I'd like to ask for a code review
for the corresponding core-libs and hotspot changes:
http://cr.openjdk.java.net/~mcimadamore/panama/8234049/
A javadoc for the memory access API is also available here:
http://cr.openjdk.java.net/~mcimadamore/panama/memaccess_javadoc/jdk/incubator/foreign/package-summary.html
Note: the patch passes tier1, tier2 and tier3 testing (**)
Here is a brief summary of the changes in java.base and hotspot (the
remaining new files are implementation classes and tests for the new
API):
* ciField.cpp - this one is to trust final fields in the foreign
memory access implementation (otherwise VM doesn't trust memory
segment bounds)
* Modules.gmk - these changes are needed to require that the
incubating module is loaded by the boot loader (otherwise the above
changes are useless)
* library_call.cpp - this one is a JIT compiler change to treat
Thread.currentThread() as a well-known constant - which helps a lot
in the confinement checks (thanks Vlad!)
* various Buffer-related changes; these changes are needed because
the memory access API allows a memory segment to be projected into a
byte buffer, for interop reasons. As such, we need to insert a
liveness check in the various get/put methods. Previously we had an
implementation strategy where a BB was 'decorated' by a subclass
called ScopedBuffer - but doing so required some changes to the BB
API (e.g. making certain methods non-final, so that we could decorate
them). Here I use an approach (which I have discussed with Alan)
which doesn't require any public API changes, but needs to add a
'segment' field in Buffer - and then have constructors which keep
track of this extra parameter.
* FileChannel changes - these changes are required so that we can
reuse the Unmapper class from the MemorySegment implementation, to
deterministically deallocate a mapped memory segment. This should be
a 'straight' refactoring, no change in behavior should occur here.
Please double check.
* VarHandles - this class now provides a factory to create memory
access VarHandle - this is a bit tricky, since VarHandle cannot
really be implemented outside java.base (e.g. VarForm is not public).
So we do the usual trick where we define a bunch of proxy interfaces
(see jdk/internal/access/foreign) have the classes in java.base refer
to these - and then have the implementation classes of the memory
access API implement these interfaces.
* JavaNIOAccess, JavaLangInvokeAccess - because of the above, we need
to provide access to otherwise hidden functionalities - e.g. creating
a new scoped buffer, or retrieving the properties of a memory access
handle (e.g. offset, stride etc.), so that we can implement the
memory access API in its own separate module
* GensrcVarHandles.gmk - these changes are needed to enable the
generation of the new memory address var handle implementations;
there's an helper class per carrier (e.g.
VarHandleMemoryAddressAsBytes, ...). At runtime, when a memory access
var handle is needed, we dynamically spin a new VH implementation
which makes use of the right carrier. We need to spin because the VH
can have a variable number of access coordinates (e.g. depending on
the dimensions of the array to be accessed). But, under the hood, all
the generated implementation will be using the same helper class.
* tests - we've tried to add fairly robust tests, often checking all
possible permutations of carriers/dimensions etc. Because of that,
the tests might not be the easiest to look at, but they have proven
to be pretty effective at shaking out issues.
I think that covers the main aspects of the implementation and where
it differs from vanilla JDK.
P.S.
In the CSR review [2], Joe raised a fair point - which is
MemoryAddress has both:
offset(long) --> move address of given offset
offset() --> return the offset of this address in its owning segment
And this was considered suboptimal, given both methods use the same
name but do something quite different (one is an accessor, another is
a 'wither'). one obvious option is to rename the first to
'withOffset'. But I think that would lead to verbose code (since that
is a very common operation). Other options are to:
* rename offset(long) to move(long), advance(long), or something else
* drop offset() - but then add an overload of MemorySegment::asSlice
which takes an address instead of a plain long offset
I'll leave the choice to the reviewers :-)
Finally, I'd like to thank Mark, Brian, John, Alan, Paul, Vlad,
Stuart, Roger, Joe and the Panama team for the feedback provided so
far, which helped to get the API in the shape it is today.
Cheers
Maurizio
(**) There is one failure, for "java/util/TimeZone/Bug6329116.java" -
but that is unrelated to this patch, and it's a known failing test.
[1] - https://openjdk.java.net/jeps/370
[2] - https://bugs.openjdk.java.net/browse/JDK-8234050
