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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
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.
3 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
Why?
§ LAPACK – Linear Algebra Package
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.”
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
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
7 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
Native Code
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JNI @since 1.1
9 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
JNI
classLibC{staticnativelonggetpid();}
jlongJNICALLJava_LibC_getpid(JNIEnv*env,jclassc){ returngetpid();}
Usage scenario
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
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
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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Java Frame
Java Heap Native Memory
Native Frame
GC roots
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Java Heap Native Memory
Java Frame Native Frame
GC roots
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jobjectraw ptr address
Java Heap
Native Memory
ptr
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jobjectraw ptr address
Java Heap
Native Memory
ptr
17 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
Java Heap Native MemoryH
andl
es
Java Frame Native Frame
GC roots
18 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
Java
Native
Java Heap
Native Memory
VM
Thread State
Anatomy of JNI call
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
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
21 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
JNI
A victim of its own success?
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
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
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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intprintf(constchar*format,...)
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voidqsort(void*base,size_tnel,size_twidth,int(*cmp)(constvoid*,constvoid*));
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JNR Java Native Runtime
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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
29 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
DEMO
§ native call – getpid
§ structs – gettimeofday
§ qsort – upcalls
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
31 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
Better JNI Easier, safer, faster!
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
33 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
Project Panama “Bridging the gap”
34 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
35 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
Better JNI
pid_t get_pid();
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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
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
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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Better JNI Faster
callq 0x1057b2eb0 ; getpid entry
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
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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Better JNI Trust Levels
Untrusted
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Better JNI Trust Levels
Trusted
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Better JNI Trust Levels
Privileged
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Better JNI
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;
47 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
Carrier Types
§ Javabooleanbyteshortcharintlong
§ Ccharshortfloatintlonglonglong
?
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Carrier Types
§ Javaboolean(uint8_t)byte(int8_t)short(int16_t)char(uint16_t)int(int32_t)long(int64_t)
§ Ccharshortfloatintlonglonglong
?
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);}
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
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
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();}
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;}
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*/}}
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();}
56 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
Better JNI Variadic Function
int printf(const char *format, ...)
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);
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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Optimize checks
void run(MyClass obj) { obj.f1(); // NPE obj.f2(); // NPE obj.f3(); // NPE }
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
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
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
63 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
Java
Java Heap
Native Memory
VM
Native
Thread State
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Java
Java Heap
Native Memory
VM
Native
Thread State
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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Native Data
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NIO @since 1.4
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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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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[]
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
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
72 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
sun.misc.Unsafe Anti-JNI
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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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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)
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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UNSAFE.putInt(new Object(), 0L, 0)
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UNSAFE.putInt(null, 0L, 0)
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UNSAFE.getObject(addr)
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Unsafe =? Fast
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Unsafe != Fast
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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”
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
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
84 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
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*
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
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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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
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
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)
91 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
Optimized Bounds Checks
//nullcheck+(indexu<array.length)returnarray[index];
int[]
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[]
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[]
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
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
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
98 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
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.
99 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
Graphic Section Divider
100 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
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)
102 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
JNI Usage scenario
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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(); }
104 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
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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§ Java Heap § Native Heap
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§ Panama – Vector API – Arrays 2.0 – Layout
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Java
Code
Data
Native
Code
Data
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GC roots
Java Heap Native Memory
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GC roots
Java Heap Native Memory
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GC roots
Java Heap Native Memory
111 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
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
112 Copyright © 2016, Oracle and/or its affiliates. All rights reserved
Java
Code
Data
Native
Code
Data