RFR (M): 8149159: Clean up Unsafe

[Christian Thalinger]

! UNSAFE_ENTRY(jobject, Unsafe_GetObject(JNIEnv *env, jobject unsafe, jobject obj, jlong offset)) {
    UnsafeWrapper("Unsafe_GetObject”);

Could UnsafeWrapper be part of the UNSAFE_ENTRY?  I mean, it’s empty anyway:

#define UnsafeWrapper(arg) /*nothing, for the present*/

> On Feb 18, 2016, at 9:22 AM, Mikael Vidstedt <mikael.vidstedt at oracle.com> wrote:
> 
> 
> Please review the following change which does some relatively significant cleaning up of the Unsafe implementation.
> 
> Bug: https://bugs.openjdk.java.net/browse/JDK-8149159
> Webrev (hotspot): http://cr.openjdk.java.net/~mikael/webrevs/8149159_unsafecleanup/hotspot/webrev.00/webrev/
> Webrev (jdk): http://cr.openjdk.java.net/~mikael/webrevs/8149159_unsafecleanup/jdk/webrev.00/webrev/
> 
> Summary:
> 
> * To avoid code duplication sun.misc.Unsafe now delegates all work to jdk.internal.misc.Unsafe. This also means that the VM - and unsafe.cpp specifically - no longer needs to know or care about s.m.Unsafe.
> * The s.m.Unsafe delegation methods have all been decorated with @ForceInline to minimize the risk of performance regressions, though it is highly likely that they will be inlined even without the annotations.
> * The documentation has been updated to reflect that it is the responsibility of the user of Unsafe to make sure arguments are valid.
> * The argument checking has, to the extent possible, been moved from unsafe.cpp up to Java to simplify the native code and allow the JIT to optimize it.
> * Some of the argument checks have been relaxed. For example, the recently introduced U.copySwapMemory does not check for null pointers anymore. See docs for j.i.m.U.checkPointer for the complete reasoning behind this. Note that the Unsafe methods today, apart from U.copySwapMemory, do not perform the NULL related check(s).
> * A test was added for j.i.m.U.copyMemory, based on U.copySwapMemory. Feel free to point out that I should merge them (because I should).
> 
> Also, unsafe.cpp was cleaned up rather dramatically. Some specific highlights:
> 
> * Unsafe_ functions are now declared static, as are the other unsafe.cpp local functions.
> * Created unsafe.hpp and moved some functions used in other parts of the VM to that. Removed some "extern" function declarations (extern is bad, kittens die when extern is (over-)used).
> * Remove scary looking comment about UNSAFE_LEAF not being possible to use - there's nothing special about it, it's just a JVM_LEAF.
> * Used UNSAFE_LEAF for a few simple leaf methods
> * Added helpful braces around UNSAFE_ENTRY/UNSAFE_END to help auto-indent
> * Removed unused Unsafe_<...>##140 functions/macros
> * Updated macro argument names to be consistent throughout unsafe.cpp macro definitions
> * Replaced some checks with asserts - as per above the checks are now performed in j.i.m.Unsafe instead.
> * Removed all the s.m.Unsafe related code
> 
> 
> Testing:
> 
> * jtreg: hotspot_jprt group, jdk/internal
> * JPRT: hotspot testset
> * Perf: JMH unsafe-bench.jar (no significant changes)
> 
> I'm taking suggestions on additional things to test.
> 
> Cheers,
> Mikael
>