working with native libraries in java - jug ru...
TRANSCRIPT
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1 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
Working with Native Libraries in Java
Vladimir Ivanov HotSpot JVM Compile r Oracle Corp.
Twitter: @iwan0www OpenJDK: vlivanov
23.04.2016
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2 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
Safe Harbor Statement
The following is intended to outline our general product direction. It is intended for information purposes only, and may not be incorporated into any contract. It is not a commitment to deliver any material, code, or functionality, and should not be relied upon in making purchasing decisions. The development, release, and timing of any features or functionality described for Oracle’s products remains at the sole discretion of Oracle.
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3 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
Why?
§ LAPACK – Linear Algebra Package
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4 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
Why?
§ LAPACK – Linear Algebra Package – written in Fortran 90 – highly optimized
§ “The original goal of the LAPACK was to … run efficiently on shared-memory vector and parallel processors.”
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5 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
Why?
§ LAPACK (Linear Algebra Package) – invoke library code – pass data into library – access data from Java
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6 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
§ Existing – Java Native Interface (JNI) & JNR library – java.nio.DirectByteBuffer – sun.misc.Unsafe (get*/set*)
§ JDK9 – j.l.i.VarHandle views over ByteBuffers
§ Future – Project Panama
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7 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
Native Code
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8 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
JNI @since 1.1
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9 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
JNI
classLibC{staticnativelonggetpid();}
jlongJNICALLJava_LibC_getpid(JNIEnv*env,jclassc){ returngetpid();}
Usage scenario
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10 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
JNI
jlongJNICALLJava_...(JNIEnv*env, jclasscls, jobjectobj){jmethodIDmid=env->GetMethodID(cls,“m”,“(I)J”);jlongresult=env->CallLongMethod(obj,mid,10);
Upcall
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11 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
JNI
jlongJNICALLJava_...(JNIEnv*env, jclasscls, jobjectobj){jfieldIDfid=env->GetFieldID(cls,“f”,“J”);jlongresult=env->GetLongField(obj,fid);jlongresult=env->SetLongField(obj,fid,10);
Data access
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12 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
JNI
§ Operations on – Classes – Strings – Arrays – Monitors
Native API: JNIEnv
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13 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
Java Frame
Java Heap Native Memory
Native Frame
GC roots
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14 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
Java Heap Native Memory
Java Frame Native Frame
GC roots
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15 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
jobjectraw ptr address
Java Heap
Native Memory
ptr
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16 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
jobjectraw ptr address
Java Heap
Native Memory
ptr
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17 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
Java Heap Native MemoryH
andl
es
Java Frame Native Frame
GC roots
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18 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
Java
Native
Java Heap
Native Memory
VM
Thread State
Anatomy of JNI call
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19 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
Java
Native
Java Heap
Native Memory
VM
Thread State
Anatomy of JNI call Safepoints
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20 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
JNI
§ Pros – seamless integration
§ looks like a Java method – rich native API to interact with Java
§ Cons – manual binding – invocation overhead
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21 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
JNI
A victim of its own success?
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22 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
JNI Sum elements
jintJNICALLJava_...(JNIEnv*env,jclassc,jobjectarr){jintlen=(*env)->GetArrayLength(env,arr);jbyte*a=(*env)->GetPrimitiveArrayCritical(env,arr,0);…returnsum;}
empty sum 1 sum 103 sum 106 JNI 11.4±0.3 ns 178±7.1 ns 798±32 ns 641±51 µs
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23 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
Critical JNI Sum elements
jintJNICALLJavaCritical_...(jintlength,jbyte*first){...returnsum;}
empty sum 1 sum 103 sum 106 JNI 11.4±0.3 ns 178.0±7.1 ns 798±32 ns 641±51 µs CriticalJNI 11.4±0.3 ns 17.2±0.8 ns 680±22 ns 636±12 µs
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24 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
Critical JNI
§ only static, non-synchronized methods supported § no JNIEnv* § arguments: primitives or primitive arrays
– [I => (length, I*) – null => (0, NULL)
§ no object arguments
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25 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
intprintf(constchar*format,...)
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26 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
voidqsort(void*base,size_tnel,size_twidth,int(*cmp)(constvoid*,constvoid*));
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27 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
JNR Java Native Runtime
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28 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
JNR
public interface LibC { @pid_t long getpid(); } LibC lib = LibraryLoader .create(LibC.class) .load("c");
libc.getpid()
Usage scenario
JNRJava
Native
bindings
Interfaces
libffi
Target
User-defined
generated on-the-fly
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29 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
DEMO
§ native call – getpid
§ structs – gettimeofday
§ qsort – upcalls
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30 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
JNR
§ Pros – automatic binding of native methods
§ Cons – manual interface extraction
§ doesn’t scale – still uses JNI to perform native calls
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31 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
Better JNI Easier, safer, faster!
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32 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
“If non-Java programmers find some library useful and easy to access, it should be similarly accessible to Java programmers.”
John Rose, JVM Architect,
Oracle Corporation
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33 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
Project Panama “Bridging the gap”
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34 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
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35 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
Better JNI
pid_t get_pid();
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36 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
Better JNI
publicinterfaceLibC{longgetpid();}LibClibc=Library .load(LibC.class,“c”);libc.getpid();
Easier
j.l.iJava
Native
bindings
Interfaces
JVM stubs
Target
User-defined
Library
generated on-the-fly
produced by jextract
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37 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
Better JNI
publicinterfaceLibC{longgetpid();}LibClibc=Library.load(LibC.class,“c”/*lib_name*/);libc.getpid();
Easier
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38 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
Better JNI
publicinterfaceLibC{longgetpid();}LibClibc=Library.load(LibC.class,“c”/*lib_name*/);libc.getpid();
Easier
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39 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
Better JNI Faster
callq 0x1057b2eb0 ; getpid entry
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40 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
Better JNI
MethodTypemt=MethodType.methodType(int.class);//pid_tMethodHandlemh=MethodHandles.lookup().findNative("getpid",mt);intpid=(int)mh.invokeExact();
Faster
getpid JNI 13.7 ± 0.5 ns Direct call 3.4 ± 0.2 ns
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41 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
Better JNI
§ no crashes § no leaks § no hangs § no privilege escalation § no unguarded casts
Safer
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42 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
Better JNI Trust Levels
Untrusted
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43 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
Better JNI Trust Levels
Trusted
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44 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
Better JNI Trust Levels
Privileged
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45 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
Better JNI
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46 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
Better JNI gettimeofday
/*time.h*/struct{time_ttv_sec;suseconds_ttv_usec;}timeval;
intgettimeofday(structtimeval*tv,structtimezone*tz);
struct{inttz_minuteswest;inttz_dsttime;}timezone;
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47 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
Carrier Types
§ Javabooleanbyteshortcharintlong
§ Ccharshortfloatintlonglonglong
?
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48 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
Carrier Types
§ Javaboolean(uint8_t)byte(int8_t)short(int16_t)char(uint16_t)int(int32_t)long(int64_t)
§ Ccharshortfloatintlonglonglong
?
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49 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
Better JNI $ jextract time.h
interfaceTime{interfaceTimeval{longtv_sec$get();voidtv_sec$set(long);longtv_usec$get();voidtv_usec$set(long);}
intgettimeofday(Timeval,Timezone);
interfaceTimezone{inttz_...$get();voidtz_...$set(int);inttz_...$get();voidtz_...$set(int);}
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50 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
Foreign Layouts
§ Native data requires special address arithmetic – Native layouts should not be built into the JVM (sorry, no native classes) – Native types are unsafe, so trusted code must manage the bits
§ Solution: A metadata-driven Layout API
§ As a bonus, layouts other than C and Java are naturally supported – Network protocols, specialized in-memory data stores, mapped files, etc.
50
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51 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
Better JNI Data Layout
interfaceTimeval{…@Offset(offset=0L)longtv_sec$get();…@Offset(offset=64L)longtv_usec$get();…§ work on Layout Definition Language (LDL) is in progress
– https://github.com/J9Java/panama-docs/blob/master/StateOfTheLDL.html
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52 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
Better JNI Runtime Librarylib=Library.create(“c”);Timetime=lib.create(Time.class);Timevaltval=lib.create(Timeval.class);intres=time.gettimeofday(tval,null);if(res==0){longtv_sec=tval.tv_sec$get();longtv_usec=tval.tv_usec$get();}
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53 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
Better JNI Resources
Timevaltval;try{tval=lib.create(Timeval.class);intres=time.gettimeofday(tval,null);if(res==0){longtv_sec=tval.tv_sec$get();longtv_usec=tval.tv_usec$get();}else{/*errorhandling*/}}finally{lib.free(tval);tval=null;}
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54 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
Better JNI Resources
interfaceTimevalextendsAutoCloseable{…}try(Timevaltval=lib.create(Timeval.class)){intres=time.gettimeofday(tval,null);if(res==0){longtv_sec=tval.tv_sec$get();longtv_usec=tval.tv_usec$get();}else{/*errorhandling*/}}
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55 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
Better JNI “Civilizer”
interfaceTimeval{voidgettimeofday(Timeval,Timezone)throwsErrNo;}try(Timevaltval=lib.create(Timeval.class)){time.gettimeofday(tval,null);//throwsexceptionlongtv_sec=tval.tv_sec$get();longtv_usec=tval.tv_usec$get();}
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56 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
Better JNI Variadic Function
int printf(const char *format, ...)
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57 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
Better JNI jextract + Civilizer
//int printf(const char *format, ...) interfaceStdio{…//Rawintprintf(Pointer<Byte>format,byte[]args);//Civilizedvoidprintf(Stringformat,Object…args);
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58 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
Optimize checks
void run(MyClass obj) { obj.nativeFunc1(); // checks & state trans. obj.nativeFunc2(); // checks & state trans. obj.nativeFunc3(); // checks & state trans. }
58
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59 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
Optimize checks
void run(MyClass obj) { obj.f1(); // NPE obj.f2(); // NPE obj.f3(); // NPE }
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60 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
Optimize checks
void run(MyClass obj) { if (obj == null) jump throwNPE_stub; call MyClass::f(obj); call MyClass::f1(obj); call MyClass::f3(obj); }
60
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61 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
Optimize checks
void run(MyClass obj) { obj.nativeFunc1(); // checks & state trans. obj.nativeFunc2(); // checks & state trans. obj.nativeFunc3(); // checks & state trans. }
61
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62 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
Optimize checks
void run(MyClass obj) { if (!performChecks()) jump failed_stub; call transJavaToNative(); MyClass::nativeFunc1(env, obj); MyClass::nativeFunc2(env, obj); MyClass::nativeFunc3(env, obj); call transNativeToJava(); }
62
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63 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
Java
Java Heap
Native Memory
VM
Native
Thread State
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64 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
Java
Java Heap
Native Memory
VM
Native
Thread State
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65 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
Better JNI
§ Native access between the JVM and native APIs – Native code via FFIs – Native data via safely-wrapped access functions – Tooling for header file API extraction and API metadata storage
§ Wrapper interposition mechanisms, based on JVM interfaces – add (or delete) wrappers for specialized safety invariants
§ Basic bindings for selected native APIs
Easier, Safer, Faster!
65
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66 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
Native Data
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67 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
NIO @since 1.4
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68 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
NIO
§ Provides access to the low-level I/O operations – Buffers for bulk memory operations
§ on-heap and off-heap – Character set encoders and decoders – Channels, a new primitive I/O abstraction – File interface
§ supports locks and memory mapping of files – Multiplexed, non-blocking I/O
“New I/O”
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69 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
java.nio.Buffer
§ java.nio.ByteBuffer / CharBuffer / … – MappedByteBuffer extends ByteBuffer
§ memory-mapped region of a file – DirectByteBuffer extends MappedByteBuffer
§ malloc’ed native memory – HeapByteBuffer
§ backed by byte[]
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70 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
java.nio.DirectByteBuffer
ByteBufferdbb=ByteBuffer.allocateDirect(size);dbb.rewind();//resetpositionwhile(dbb.hasRemaining()){byteb=dbb.get();}
Usage
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71 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
java.nio.Buffer
§ < 2GiB – ByteBuffer.allocateDirect(int size)
§ Stateful – Buffer.position – not thread-safe
§ Resource deallocation – GC-based (Cleaner) memory management
§ Zeroing – on initialization
§ Bounds checking
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72 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
sun.misc.Unsafe Anti-JNI
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73 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
sun.misc.Unsafe
Use case Example methods
Concurrency primitives compareAndSwap*
Serialization allocateInstance
Efficient memory management, layout, and access
allocateMemory/freeMemory get*/put*
Interoperate across the JVM boundary get*/put*
… …
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74 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
sun.misc.Unsafe
§ Unsafe.get*/put* – getInt(Object base, long offset) – putInt(Object base, long offset, int value);
§ double-register addressing mode – getInt(o, offset) == o + offset – getInt(null, address) == address
§ long allocateMemory(long size)
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75 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
sun.misc.Unsafe
§ Absolute addresses – byte getByte(long address) – int getInt(long address) – …
§ Object getObject(long address)?
§ long getAddress(long address)
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76 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
UNSAFE.putInt(new Object(), 0L, 0)
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77 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
UNSAFE.putInt(null, 0L, 0)
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78 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
UNSAFE.getObject(addr)
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79 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
Unsafe =? Fast
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80 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
Unsafe != Fast
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81 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
Unsafe != Fast
§ public native Object allocateInstance(Class<?> cls) throws …;
§ Array index vs raw offset long[]base=newlong[…];intidx=…;longoffset=(((long)idx)<<SCALE+OFFSET)longvalue=Unsafe.getLong(base,offset);
§ JDK-8078629: “VM should constant fold Unsafe.get*() loads from final fields”
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82 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
- How many of you have used the Unsafe API? …
John Rose, JVM Architect, Oracle JVM Language Summit 2014
82
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83 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
- How many of you have used the Unsafe API? …
- A lot of you. Gosh. I'm sorry.
John Rose, JVM Architect, Oracle JVM Language Summit 2014
83
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84 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
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85 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
sun.misc.Unsafe
Use case Example methods
Concurrency primitives compareAndSwap*
Serialization allocateInstance (ReflectionFactory.newConstructorForSerialization)
Efficient memory management, layout, and access
allocateMemory/freeMemory get*/put*
Interoperate across the JVM boundary
get*/put*
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86 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
sun.misc.Unsafe
Use case Replacement
Concurrency primitives JEP 193 Variable Handles
Serialization Reboot JEP 187 Serialization Improvements
Efficient memory management, layout, and access
Project Panama, Project Valhalla, Arrays 2.0, Better GC
Interoperate across the JVM boundary
Project Panama, JEP 191 Foreign Function Interface
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87 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
java.lang.invoke.
VarHandle @since 9
JEP 193: Variable Handles
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88 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
VarHandle
MethodHandles.Lookup:VarHandlebyteBufferViewVarHandle(Class<?>viewArrayClass,booleanbigEndian){…}
“Produces a VarHandle giving access to elements of a ByteBuffer viewed as if it were an array of elements of a different primitive component type to that of byte, such as int[] or long[].”
ByteBuffer View
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89 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
VarHandle
VarHandleVH=MethodHandles.byteBufferViewVarHandle(int[].class,ByteOrder.nativeOrder()==ByteOrder.BIG_ENDIAN);ByteBuffer dbb = ByteBuffer.allocateDirect(size); int v = (int)VH.get(dbb, idx);
ByteBuffer View
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90 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
java.nio.ByteBuffer vs VarHandle View
DirectByteBuffer VarHandle Size < 2 GiB < 2 GiB State Yes No Resource management GC-based No (delegates to DBB) Zeroing Yes No (delegates to DBB) Bound checks Yes (optimized) Yes (optimized)
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91 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
Optimized Bounds Checks
//nullcheck+(indexu<array.length)returnarray[index];
int[]
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92 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
Optimized Bounds Checks
//boundsandnullcheckif(index<0||index>=array.length)thrownew…();longoffset=BASE+(((long)index)<<2);returnUNSAFE.getInt(array,offset);
int[]
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93 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
Optimized Bounds Checks
//boundsandnullcheckindex=Objects.checkIndex(index,array.length);longoffset=BASE+(((long)index)<<2);returnUNSAFE.getInt(array,offset);
@HotSpotIntrinsicCandidatepublicstaticintcheckIndex(intindex,intlength,…);
int[]
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94 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
“Если не Unsafe, то кто: восход VarHandles”
Алексей Шипилёв, Oracle
Сегодня, 17:20, Зал №1
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95 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
§ Existing – Java Native Interface (JNI) & JNR library – java.nio.DirectByteBuffer – sun.misc.Unsafe (get*/set*)
§ JDK9 – j.l.i.VarHandle views over ByteBuffers
§ Future – Project Panama
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96 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
http://openjdk.java.net
Project Panama Foreign Function Interface Data Layout Control Vector API Arrays 2.0
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http://openjdk.java.net
Project Panama [email protected]://hg.openjdk.java.net/panama/panama
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Safe Harbor Statement
The preceding is intended to outline our general product direction. It is intended for information purposes only, and may not be incorporated into any contract. It is not a commitment to deliver any material, code, or functionality, and should not be relied upon in making purchasing decisions. The development, release, and timing of any features or functionality described for Oracle’s products remains at the sole discretion of Oracle.
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99 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
Graphic Section Divider
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Vector API
bits Java x86 reg 8 byte al 16 short ax 32 int eax 64 long rax 128 - xmm0 256 - ymm0 512 - zmm0
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Vector API
§ MIMD (SPMD), SIMD, SIMT (GPGPU)
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JNI Usage scenario
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103 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
JNI
Java: public class GetPid { public static native long getpid(); }
C/C++:
get_pid.h: JNIEXPORT jlong JNICALL Java_GetPid_getpid (JNIEnv *, jclass); get_pid.c: jlong JNICALL Java_GetPidJNI_getpid(JNIEnv *env, jclass c) {
return getpid(); }
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JNI: Method Invocation
1. if (GC_locker::needs_gc()) SharedRuntime::block_for_jni_critical()
2. transition to thread_in_native 3. unpack array arguments
4. call native entry point
Runtime checks before and after native call
1. call native entry point 2. check for safepoint in progress
3. check if any thread suspend flags are set – call into JVM and possibly unlock the
JNI critical if a GC was suppressed while in the critical native
4. transition to thread_in_Java
5. return
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105 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
§ Java Heap § Native Heap
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106 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
§ Panama – Vector API – Arrays 2.0 – Layout
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107 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
Java
Code
Data
Native
Code
Data
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108 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
GC roots
Java Heap Native Memory
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109 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
GC roots
Java Heap Native Memory
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110 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
GC roots
Java Heap Native Memory
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java.nio.ByteBuffer
public final ByteBuffer alignedSlice(int unitSize) { /** * Creates a new byte buffer whose content is a shared and aligned * subsequence of this buffer's content.
public final int alignmentOffset(int index, int unitSize) {
§ /** * Returns the memory address, pointing to the byte at the given index, * modulus the given unit size. * * @apiNote * This method may be utilized to determine if unit size bytes from an * index can be accessed atomically, if supported by the native platform. *
@since 9
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112 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
Java
Code
Data
Native
Code
Data