1 / 19

Java Virtual Machine (JVM)

Java Virtual Machine (JVM). Reasons for learning JVM Resource The Java TM Virtual Machine Specification (2 nd Ed), by Tim Lindholm & Frank Yellin, Addison-Wesley,1999 http://java.sun.com/docs/books/vmspec/. JVM Types and Words.

mschwab
Télécharger la présentation

Java Virtual Machine (JVM)

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Java Virtual Machine (JVM) • Reasons for learning JVM • Resource • The Java TM Virtual Machine Specification (2 nd Ed), by Tim Lindholm & Frank Yellin, Addison-Wesley,1999http://java.sun.com/docs/books/vmspec/ by Neng-Fa Zhou

  2. JVM Types and Words • byte, char, short, int, float, reference, and returnAddress in one word • boolean, byte, char, and short are converted to int • Special representations for byte, char, and short arrays are possible • long and double in two words by Neng-Fa Zhou

  3. JVM Architecture PC Method area OPTOP Operand stack EP Environment Heap Local vars LVARS ….. Registers Stack by Neng-Fa Zhou

  4. Data Areas of JVM • Method area (shared by all threads) • One record for each loaded class that contains: • Constant pool • Code for methods and constructors • Heap (shared by all threads) • One record for each class instance or array • Stack (one per thread) • Hold frames associated with method invocations by Neng-Fa Zhou

  5. Stack Frame Structure Operand stack: Evaluate expressions Pass method arguments and receive results Local variables: Addressed as word offsets Constant pool: Dynamic linking Operand stack Environment Constant pool PC EP LVARSLocal variables by Neng-Fa Zhou

  6. The class File Format ClassFile {     u4 magic;     u2 minor_version;     u2 major_version;     u2 constant_pool_count;     cp_info constant_pool[constant_pool_count-1];     u2 access_flags;     u2 this_class;     u2 super_class;     u2 interfaces_count;     u2 interfaces[interfaces_count];     u2 fields_count;     field_info fields[fields_count];     u2 methods_count;     method_info methods[methods_count];     u2 attributes_count;     attribute_info attributes[attributes_count];     } by Neng-Fa Zhou

  7. Names and Descriptors • Class, method, and field names are all stored symbolically as strings • A descriptor is a string representing the type of a field or method • Class names • Class names are always fully qualified • Use forward slash rather than dot as the delimeter • Ex: Java.util.Vector =>java/util/Vector by Neng-Fa Zhou

  8. Descriptors • Primitive types • B, C, D, F, I,J(long), S, Z(boolean), V(void) • Arrays • Use [ • Classes • Lclassname • Ex: • Type:String valueOf(char[] , int offset, int count) • Descriptor:([CII)Ljava/lang/String; by Neng-Fa Zhou

  9. Constants • CONSTANT_Class • CONSTANT_Fieldref • CONSTANT_Methodref • CONSTANT_InterfaceMthodref • CONSTANT_String, • CONSTANT_Integer • CONSTANT_Float • CONSTANT_Long • CONSTANT_Double • CONSTANT_NameAndType • CONSTANT_Utf8 by Neng-Fa Zhou

  10. field_info Access flags Name Descriptor Static values method_info Access flags Name Descriptor Code field_info and method_info by Neng-Fa Zhou

  11. Instruction Set • Load and store (e.g., iload, istore ldc, iconst_<i>) • Arithmetic (e.g., iadd, isub, imul, idiv, irem) • Type conversion (e.g., i2b, i2f, i2d) • Object creation and manipulation(e.g, new, newarray, iaload, iastore , getfield, putfield) • Operand stack manipulation (e.g., pop, dup, dup_x1, swap) • Control transfer (e.g., goto, ifeq, tableswitch) • Method invocation and return (invokevirtual, invokeinterface, invokespecial, invokestatic, ireturn) • Exception handling and synchronization (e.g.,athrow) by Neng-Fa Zhou

  12. Compiling for JVMConstants, Local Variables, and Controlconstructs void spin() { int i; for (i = 0;i<100;i++) ; } Method void spin() 0 iconst_0 // Push int constant 0 1 istore_1 // Store into local variable 1 (i=0) 2 goto 8 // First time through don't increment 5 iinc 1 1 // Increment local variable 1 by 1 (i++) 8 iload_1 // Push local variable 1 (i) 9 bipush 100 // Push int constant 100 11 if_icmplt 5 // Compare and loop if less than (i < 100) 14 return // Return void when done by Neng-Fa Zhou

  13. Compiling for JVMReceiving Arguments and Invoking Methods int m1(int a1, int a2) { return m2(2,3,a1,a2);} Method int m1() 0 aload_0 // Push local variable 0 (this) 1 bipush 2 // Push int constant 2 3 bipush 3 // Push int constant 3 5 iload_1 // Push local var a16 iload_2 // Push local var a27 invokevirtual #4 // Method Example.m(IIII)I 10 ireturn // Return int on top of operand stack by Neng-Fa Zhou

  14. Compiling for JVMWorking with Class Instances MyObj example() { MyObj o = new MyObj(); return silly(o); } Method MyObj example() 0 new #2 // Class MyObj 3 dup 4 invokespecial #5 // Method MyObj.<init>()V 7 astore_1 8 aload_0 9 aload_1 10 invokevirtual #4 // Method Example.silly(LMyObj;)LMyObj; 13 areturn by Neng-Fa Zhou

  15. Compiling for JVMArrays Creating arrays Manupulating arrays int x[] = new int[3];0 iconst_31 newarray int3 astore_1 x[2] = 0;4 aload_1 5 iconst_2 6 iconst_0 7 iastore x[0] = x[2]; 8 aload_1 9 iconst_010 aload_111 iconst_2 12 iaload13 iastore by Neng-Fa Zhou

  16. Compiling for JVMSwitches Method int chooseNear(int) 0 iload_1 1 tableswitch 0 to 2: 0: 28 1: 30 2: 32 default:34 28 iconst_0 29 ireturn 30 iconst_1 31 ireturn 32 iconst_2 33 ireturn 34 iconst_m1 35 ireturn int chooseNear(int i) { switch (i) { case 0: return 0; case 1: return 1; case 2: return 2; default: return -1; } } by Neng-Fa Zhou

  17. Compiling for JVMManipulation of the Operand Stack public long nextIndex(){ return index++; } private long index = 0; Method long nextIndex() 0 aload_0 // Push this 1 dup // Make a copy of it 2 getfield #4 // One of the copies of this is consumed // pushing long field index, // above the original this 5 dup2_x1 // The long on top of the operand stack is // inserted into the operand stack below the // original this 6 lconst_1 // Push long constant 1 7 ladd // The index value is incremented... 8 putfield #4 // ...and the result stored back in the field 11 lreturn // The original value of index is left on // top of the operand stack, ready to be returned by Neng-Fa Zhou

  18. Compiling for JVMException Handling void catchOne() { try { tryItOut(); } catch (TestExc e) { handleExc(e); } } Method void catchOne() 0 aload_0 // Beginning of try block 1 invokevirtual #6 // Method Example.tryItOut()V 4 return // End of try block; normal return 5 astore_1 // Store thrown value in local var 1 6 aload_0 // Push this 7 aload_1 // Push thrown value 8 invokevirtual #5 // Invoke handler method: // Example.handleExc(LTestExc;)V 11 return // Return after handling TestExc Exception table: From To Target Type 0 4 5 Class TestExc by Neng-Fa Zhou

  19. Review Questions • Does the efficiency of a program change after an int variable is changed to byte? • When does dynamic loading take place? • When does dynamic linking take place? • Why are run-time byte-code verification and type checking necessary? • How are exceptions handled in JVM? • How different is the JVM from a stack machine for Pascal? by Neng-Fa Zhou

More Related