CSI402 Systems Programming Spring 1999
COURSE LOG
Lecture 1 (1/27)
Some Course Policies:
Prerequisites: CSI310 and CSI333 are critical for success.
Incompletes: None will be given except
under extenuating circumstances that begin after drop day, and only to
people who have
Passing: At least one project must earn at least 20% before
the midterm, and at least one project must earn at least 20% after the
midterm. (Passing means at least a D)
Don't plan to get by with just the minimum.
Grading: 50% weight for projects, 50% weight for exams.
Midterm: will be given in two lecture centers,
outside of class time, to be announced.
Textbooks, email addresses, office hrs, etc: See course web page.
Subject is about
(1) Details of how programs, especially multiple source module
ones, get compiled, loaded into the computer and execute there.
(2) Introduction to programming with system facilities:
files, system calls, libraries, etc.
(3) Big projects whose specifications combine many features and use
details from real industry documents.
First view of first project: text based command processor.
Runtime information can be passed to already compiled programs via
(1) command line arguments and
(2) the environment.
(1) uses first 2 arguments of main(),
(2) uses 3rd argument of main(),
or (global variable) char **environ;
(or system library functions)
Slide showing ragged array data structure, argc, argv, env, and legal
environment strings.
USER=sdc example
What a dictionary is, key, value.
How to achieve consistancy
of implementing and calling functions of a module,
use of header files,
preprocessor #include operation,
dictionary.c example
Separate files for
module implementation, interface specification and use.
dictionary.c, .h and main.c example introduced.
Lecture 2 (1/29)
Full Notes.
Compilation Steps Diagram.
Project1 Part1 assignment handed out.
Details of steps performed by compiling a compilation unit.
dictionary.h, .c and main.c details.
Obtaining type safe function use,
avoid calling a function with argument types different from what the
function implementation expects.
Module implementation, module user and module interface specification
How done in C/C++ with files
Declarations and definition,
signature of a function.
What extern means
Multiple declarations
declaration plus definition in the same compilation unit are OK,
see example
Definition helps produce memory allocation and address assignment.
Lecture 3 (2/1)
Design Sketch of the demo program(.ps)
3 Modules:
Command interface
insert, retrieve.
You add delete, dump
StringDict module
StringDict uses Listof2CharPtrs
Design described
with modified UML-like diagram showing data structures.
StringDict takes care of managing the keys and values as strings.
Listof2Ptrs is used by StringDict
to manage a list of char pointer pairs.
Walk through files main.cc showing
StringDict instance and command interface
Lecture 4 (2/3)
How data members of structs are referenced
variable.name name
(with the member function invocation associated with this object.
this->name
(*this).name
New ideas about member functions and structures:
(1) function to operate on the structure is
declared within
and thus tightly connected with that structure type.
Those functions are called member functions.
(2) Every member functions invocation is associated
with an instance of the structure
that contains the member function.
(3) Structure elements (members)
may be accessed from within the member function invocation
by their (field) name
or via the "this" pointer
C++ structs ARE classes whose member protections
specifiers start with public: (instead of private:)
Walk through code with pager
demo is C++ code
demoC
translation into C that uses variables named "this"
to illustrate the "this" pointer.
Walk through with debugger
under EMACS M-x gdm
Print value of argv[1] and argv[0] with debugger-
see pointer (Hex) value expression
plus the string for convenience.
Observe calls to initializers.
Lecture 5 (2/5)
Project 1-Part 2 assigned, due 2/17
.PS
.PDF
Interactive command loop,
scan an indefinite number of tokens,
suggest array of char *,
pointer variable to it is char **,
use strtok initially.
Three storage extents of C/C++
Each extent is implemented by a different
region in virtual memory.
How to specify each extent in C/C++
C/C++ function parameters (except reference) are automatic extent.
Pitfalls of automatic variables
Local scope
(2 different variables with the same name)
Uninitialized by default
Risk of pointer with illegal address
Static extent
Dynamically allocated by new, malloc, calloc
Importance of only using properly allocated space,
cause of "illegal addess" or "bus error" crashes,
consequence of using a bad pointer to accessible space
(hard to find bugs)
Lecture 6 (2/8)
Review of 3 storage extents and what extent means.
optional extant qualifier "auto"
calloc clears allocated space, malloc doesn't
Example situations that require static extent:
Function call counter.
(initialization done once for each allocation operation)
Stopwatch facility required in project.
Slide
Combinations of (name) scopes with variable extents
Scopes:
What a name is
Same identifier name different variables.
Local (to function) scope
Compilation unit (local symbol) scope
Global (global symbol) scope
Unfortunate two different meanings for "static" qualifier
Optimizing compilers allocate automatic variables to registers
Slide
Responsibility of program designer to design storage allocation policy.
Slide
Storage management policies:
A "client" is a module that initiates a service request
"selfish" (most common)
occurs when the module uses an automatic variable
examples
cin >> buff;
times system call required for project.
how to read the man page from man -s 2 times
"lender"
readdir facility use required for project.
Slide
------------------------------------------
Reading reference on C extents and scopes:
Harbison and Steele:
Section 4.3 Storage Class Specifiers
Lecture 7 (2/10)
Storage management policies for items in current project
Policies:
Extent (3 kinds)
Ownership
Owner is the module that reclaims, ie.
deletes, destroys, deallocates the storage unit
Failure to reclaim
dynamic memory causes "memory leakage"
(automatic memory causes stack overflow,
that is caused by recursions that do not return)
See Maguire's Solid Code book for lots of philosophy on storage management
Items in project:
() StringDict
StringDict is revised now in demo-part2:
Documentation added to StringDict.h
demo.cc now runs delete[] on value string pointer returned
by dict.retrieve( ... )
StringDict manages storage for key and value strings
all by itself. It never passes ownership away nor
takes ownership. key and value strings are copied when
they are stored.
() command input and tokenization by strtok
OK to decompose and insert '\0' in the static extent variable
named buffer in the command reader module for project items
1-15 since that processing
does not increase the length of each token
token strings are not needed after use by each command
item 16 DOES require getting new space for quoted tokens
because variable substitution can increase the length
Example:
>>>> import
>>>> tokens "$PWD"
token[0]: tokens
token[1]: /home2/classes/csi402/public_html/pub/LectureMaterial
() ls
IF you use system("ls") you will lose credit because it is too easy!!
See man directory. readdir is a "lender" service. New calls to
readdir make the pointers returned by the older calls into garbage
() stopwatch
Clients of the times() system call are selfish. You must allocate
space a for the struct tms and pass a pointer P to this space by
calling times(P)
This policy is just like cin >> somevar;
cin.operator<<( ... ) writes data into your variable somevar
State diagram describing the operation of the stopwatch
Explanation of stopwatches used in clocked sports (basketball, hocky, football, etc)
2 states ON, OFF
How -zero, -on, and -off commands make the states change.
Need for persistant (static extent) storage to store
stopwatch state and the times counts when the stopwatch was started from 0.
() environment
See various Unix resources about the environment, and log in to eve, type
printenv and see what comes out.
Demo slide of using gdb to view types and values of
env, *env, **env, env[0], env[1] etc
Slide(unspaced)
Slide(spaced)
Lecture 8 (2/12)
Environment applications, environment (ragged array) structure,
copying an environment string requires
(1) obtaining its length (strlen can be used)
(2) allocating space for your copy (requires length+1 bytes)
(3) actual copy (strcpy can be used)
Lexical Scanning and Table driven programming
Ref: Beck 5.1.2
Write program logic by filling in a table rather than by writing statements.
Outline for invoking table driven scanner for part2 project:
Code simple scan to find beginning of each token. If the
token begins with ", use table driven scanner.
If not, use say strtok to find the end.
"PAC-man" slide. Use of end-of-input or "Tack".
Scan step action:
1. Determine the class of the current character
2. Based on scanner's
*current state
*class of current character
->perform an action
->change state
3. "Gobble" the current character
exit when state is an exit state
Glimpse at scanner code:
classify()
enumerated type for states.
struct transition
represents ONE ARROW coming out of ONE state
has 3 components: ch_class, new state, action
arrays of transitions
state table drawn on blackboard (array of *tranition)
(See also notes.txt in the Lecture08 directory)
Lecture 9 (2/17)
Meanings compared:
char A[100]; char *pch="xxx"; char B[]="yyy";
Function pointer explanation and demo program.
(1) Declaring function pointer variables.
(2) Loading a function pointer value into a function
pointer variable
(3) Calling the function pointed to by a function pointer
variable
Quick glimpse at the scanner operation.
Lecture 10 (2/19)
Details of Scanner Demo design and code.
Design Slide (.ps, .pdf )
Public interface:
Analysis structure, storage management,
specifying scan extent
fsa structure: Cursor, state, symbol, buf, extent
Basic scanner theory (again)
Table representation
Scanner loop walkthrough (Scanner.C)
compared to theory slide
Use of action functions, what they return
Use of variable "Mark" to preserve beginning
position of a token.
Lecture 11 (2/22)
Formats must be "exact" for full credit.
Internet service protocols specify exact spellings of
keywords used in conversations over network connections.
email client (pine, elm, mail, browser email) converses with server
"RFC"s contains the standards
Build steps reviewed, understanding them is important for
understanding the problem solved by make and how make works
Executing a file, "x" indicator of in ls -l listing
Shell script
Magic number #! at the beginning of a Unix executable file
means run the program named on the first line with standard
input this file.
Shell script saves typing effort, is like DOS/Win .bat file
RCS database required for build.sh as with all other project files.
Question on what ci -l means
Type safe linkage and mangled names
using say strcpy(45,22,96) in a C program
is not detected, but in C++, the
class of a member function, the name, and the
types of arguments are coded in a "mangled"
name or symbol
Lecture 12 (2/24)
Reading for next project: As assigned for part1, assembling, skip relocation for
now, Beck chapter 3 on absolute loading (no relocation for now)
Patterson and Hennessy, review MIPS processor and assembly language.
Overview of project2.
Lecture 13 (2/26)
Introduction to the cpu component of project2.
cpu will use the tester (person) as memory by default,
should also accept 512 bytes of MIPS instructions in a file.
Basic bus oriented computer architecture, bus errors.
Introduction to MIPS instruction interpretation.
Hexadecimal and binary.
ADDIU instruction interpretationin detail.
You can get MIPS instructions from software in ~csi402/usr/bin
or from spim (installed in CSC unix cluster)
16 to 32 bit sign extension and 2-s complement arithmetic
used in ADDIU instruction,
example of why 0xFFFFFFE0 is -32
What overflow means: wrong arithmetic result.
2-s complement overflow is detected by carries out of
sign bit and bit next to sign bit being unequal.
Year 2000 overflow example.
unsigned binary represents only positive or 0 integers.
Lecture 14 (3/8)
Project 4 Assigned
All work (except README files for messages to the TAs)
must be submitted as RCS databases in an RCS directory
RCS database must include RCS/Makefile,v (produced
by ci -l Makefile)
For full credit,
gmake cpu
must generate an executable file named cpu.
Review of args of main to provide command line arguments
for spec. 1
See Topics in C on ragged arrays if necessary
Use of global variables to record options
(Question on why main(int argc, char *argv[argc] ) cannot
be done in C/C+)
State report format
for spec. 2,3
see ~csi402/pub/Project2/Messages
in particular, demo-MP.C, MP.h
slide of demo-MP run
Initialization of state
for spec. 3
report should print state before the next instruction execute
Basic fetch m[PC], execute, set new PC value loop
The 5 steps that suffice to execute every MIPS instruction
Lecture 15 (3/10)
Examples of MIPS instruction interpretation
~csi402/pub/Project2/RISCSimulation/InstrExamples.txt
The 5 basic RISC pipeline stages
When done in sequence, they suffice for all instruction types
~csi402/pub/Project2/RISCSimulation/soutline.txt
Use of mask and shift to extract bit fields
Signed and unsigned integers pairs with the same bit patterns
can compare oppositely (see sign-types.C)
Lecture 16 (3/12)
Exam: 1hr, 1sheet of notes.
Topics for exam: Concepts and programming techniques from projects
Executable program build steps:
Preprocess (header files), compile, assemble, link
Separate compilations
Command line args and environment
Dictionaries
Member functions of C++ struct,
how to access structure instance
"for which a member function is called"
Declarations versus definitions, undefined symbol
linking errors, extern
Modules (software design concept)
Tools: RCS, gdb
Storage extents:
what they mean
how to specify each
pitfalls, dangling pointers
Memory management policies
steps needed for using dynamic ("new operator") memory
pointers
ownership
Lexical scanning
simple scanner design
express design in table using C/C++ initializers
table loop driver
function pointers
Accessing and using directories, system time, stopwatch
What is overflow
MIPS instructions
Registers
Field extraction (using mask and shifts)
Interpreting a few instruction types from examples
that will appear in ~csi402/pub/Project2/Tests
How to specify signed or unsigned integer comparison
in C/C++
How to prepare for the exam:
"object for which a member function is called"
C++ struct member function review
defining an object (instance) allocates memory
invoking a member function
referring to instance data members in the member function body
the "this" pointer; (*this).pnext, this->pnext
How to start the project:
Explore all of ~csi402/pub/Project2
Messages subdirectory: formats for input and output
RISCSimulation subdirectory: Supplemental information
Care in use of C types is needed for accurate simulation
Integer comparison (<) depends on type (signed or unsigned)
of its operands.
C++ examples (see Lecture16 directory)
C Types: (see C_types_quotes)
A type is a set of values and operations.
C integers must use binary representation
Lecture 17 (3/15)
The types of the operands determine what operation the
operator symbol does
Examples: float, unsigned int, signed int
Unsigned ints use straight binary representation
Signed int (generally) use 2-s complement binary representation
Type of operands determines the kind of comparison done
When types are mixed, promotion rules are used to convert
to a common type to which the operator can apply.
signed int SI; unsigned int UI;
if( SI == UI ) { ... }
C/C++ rule here: Promote to unsigned!
The type of a pointer P
determines the operations in expressions with *P
long unsigned int *P;
if( (*P) < 0 ) { // Never reached, since unsigned values
// are never negative
}
if( static_cast(*P) < 0 ) {// sign bit == 1}
P++ increments an ADDRESS by 4, since
4 == sizeof(long unsigned int)
Demonstration of byte orderings beginning with the first 4 bytes
of an ELF file.
Endianness:
RULE 1: Memory is Byte Addressable. Model of memory: Array of bytes
each byte is 8 bits.
Here is BIG ENDIAN,
also known as Most Significant Byte byte ordering,
also known as Left to Right ordering
0 1 2 3 4 5 . . . . 28 29 2a 2b . . . <- address
--------------------------------------------
1 9 9 5 <- contents
Address is 28
1 is the HIGH digit
RULE 2: A MULTI-BYTE unit is ALWAYS addressed by the LOWEST NUMBERED
BYTE ADDRESS of its bytes.
Here is LITTLE ENDIAN,
also known as Least Significant Byte byte ordering
also known as Right to Left ordering
. . . 2b 2a 29 28 . . . . 5 4 3 2 1 0 <- address
--------------------------------------------
1 9 9 5 <- contents
Address is 28
5 is the LOW digit
RULE 3: Hardware processes data in multibyte units correctly.
(X & 0xFF) == low byte (ALWAYS)
((X >> 24) & 0xFF) == high byte (ALWAYS)
Lecture 18 (3/17) Midterm Exam
Lecture 19 (3/19)
More on byte order
Delayed branches: what they mean
Reason for delayed branches explained in terms of
pipelined operation of the processor.
Demonstration of opertion of the 5 stage pipeline with slides.
Overflow intro
Lecture 20 (3/22)
Make
Reason for the make utility
Review of inputs and build operation for the dictionary demo.
Rules are basic components of the Makefile
Target, Dependencies, Commands are the 3 parts of a rule
The (recursive) make algorithm
Integer addition/subtraction overflow meaning and detection.
Lecture 21 (3/24)
Make: Builtin rules
Basic memory concepts:
Data storage facility
Addresses
DATA and ADDRESS are conceptually DIFFERENT
Unformatted file reading
Lecture 23 (3/29)
Virtual Memory
Pr2 is not a hardware simulator, it is a process simulator
Process: one "running" of a program
A program is static software, an executable file
Processes have resources, which are parts of a virtual
(sometimes called abstract) machine
(Virtual DOS machines used in Windows95/NT)
Each process runs in its own virtual machine instance
Different processes do not interfere
Multitasking or multiprocessing operating system
Hardware CPU is time shared among the processes
Scheduler: Part of the operating system that chooses
which process is running by the hardware CPU now
ps command
ps aux displays all processes
ps displays just your processes
Virtual memory resource contains:
data (free-store (new, dynamic), constants. C++ variables)
stack (automatic (local) variables, return addresses)
use gdb where command to see stack trace
code (copied from the executable file
when the process is started)
CPU resource: registers, PC,
ability to fetch and execute instructions,
ability to load and store data
between registers and virtual memory
System Calls: an interface to operating system services
Lecture 24 (3/31)
Virtual memory support hardware in MIPS (the translation
lookaside buffer), explained using diagrams from the
MIPS R4000 User Manual.
Lecture 25 (4/7)
How to simulate virtual memory.
Page alignment.
Lecture 26 (4/9)
Reading and processing an ELF file
Symbols defined in some object files and referenced from
other object files illustrated with symbol table listings
obtained from ELF object and executable files from the
StringDict demo project.
Symbol table listings
Symbols are defined relative to a section.
How symbols are listed as undefined.
See linking slide
Review of mangled symbols used for member functions.
Lecture 27 (4/12)
Reference to Beck's book sections 3.1 and 3.2
402 object file == Beck's control section
402 section == Beck's "different parts" page 169, problem 16
402 segment == not discussed, should have been in Chapter 6
page: Unit of allocation of physical/virtual memory
Relocation and linking.
Lecture 28 (4/14)
Relocation and linking illustrated with Beck's material
in detail.
Modification Records.
Use of symbol table: defined and undefined symbols.
Lecture 29 (4/16)
Illustration of ELF object files and their sections
linked to form an executable file, then the executable
file is used to initialize the processes virtual memory.
Linking and Loading slide
Lecture 30 (4/19)
Description of Project 3
(cooperative dictionary editing)
Grading Policies: only RCS databases accepted,
Log must record what work you did,
we might or might not compile and test
submitted programs
What a process means
Resources: CPU, virtual memory
Sometimes "process" refers to the
virtual memory only, and it can
contain multiple abstract CPUs
called threads
Interprocess communication using sockets
Server is the passive listening process
Client performs connect operation
Data is passed through the connection
by being written by write() by sender
and read by read() by the recipient.
Lecture 31 (4/21)
C++ iostream and C stdio file
access functions:
ifstream constructor, fopen
C++: Myfile << var; Myfile.read(pch,count)
C: fread(FILE *, pch, count)
Pathnames, current directory in unix
cd, pwd commands
Absolute and relative pathnames
Low level Unix functions
open, read
File descriptor (int) numbers, handles
File descriptor 0 is standard input
Blocking reads, discussion for terminal
input (read call blocks until ENTER key is pressed)
Return value of read:
-1 for error, use of errno and perror()
0 for end of file,
positive value equals actual number of chars read.
Computer Demonstration of ClientServer demo program
What happens when a second client is started
when the first client is still connected,
and when the first client exits.
Lecture 32 (4/23)
Walkthru of client.C code.
socket function
return value, errno and perror use.
return code of a process returned by exit()
A process is usually created by another process
called the parent.
Parent can receive the return code
via the wait() system call
The shell is the parent for programs you run
The shell can print the return code with
echo $? (<-CORRECTED!!)
Address family
Need for a rendezvous address.
AF_UNIX uses file name tree names
AF_INET uses IP address/port number pairs
32 bit Internet Protocol Addresses, to
become 128 bit IPv6 addresses in the future.
connect function
socket number (file descriptor)
address structure
address structure length
Address structure details
how program fills them
write function
return value, test of it
read function (brief)
implicit synchronization with server process.
Lecture 33 (4/26)
See Lecture33/misc.txt
Kochan and Wood good for files, read, write and shells
Use netstat -a (and read the man page) to observe sockets
Use of netstat -a | grep mysocket
grep = "(g)eneral (r)egular (e)xpression (p)arser"
Client/Server program operation and interaction timeline.
Building the address structure:
sockaddr_un and sockaddr types, why and how casting is used.
Lecture 34 (4/28)
How are the characters written by Process A's write
transmitted to Process B's read?
The operating system or operating system and networking
infrastructure does the job.
This question is analogous to asking how the
characters you type on the keyboard get
to the char array BUFFER in the code
char BUFFER[BUFSIZE]
cin.getline(BUFFER, BUFSIZE);
Flow Control problem in stream connections,
Stream connection means the channel does not provide
message boundaries
Explained
It is an example of DEADLOCK,
studied in operating systems courses
Solutions based on application level protocol
Fixed message size
Termination sequence, escape sequences, use of scanner
Message composed of header and body with the body
length coded in the header (used in http)
Computer Demo of the Threader program
Please read Threader.C code, how to run threader
Demonstration of the multiple threads' outputs
interfering with each other.
Unix Virtual memory layout:
Class Slide Images
Linking and Loading slide: See Virtual memory at the bottom
Code, data, free-store at lower addresses,
environment, argv, and stack at higher addresses.
Threads: Multiple CPUs running on the SAME virtual memory.
Each thread has its own stack region
within that one virtual memory space.
Lecture 35 (4/30)
Threader demo program useage instructions
Threader program outline
Draw the threads in...
Process is ONE virtual memory plus one or more CPU,
each CPU runs one thread
Each CPU has its own PC and register set
Threading is an easy to program and efficient way
to make applications work on several tasks
concurrently (to be defined)
Dictionary server that server many simultaneous
client is an example
Client and Server terminology
Server is started ahead of time, waits for
"passive opening" of connections
Client initiates an connection, it performs
an "active open"
Diagram of non-threaded server and client
Diagram of threaded server
Diagram of single process memory
used by multiple threads
Separate threads have separate stacks.
Lecture 36 (5/3)
Using threads
#include
g++ -g -c -D_REENTRANT threaded.C
g++ -o executablename threaded.o -lpthread
DO NOT USE STRTOK or other thread unsafe functions!!
USE ONLY automatic (i.e.,stack) or free-store ("new or malloc")
memory for variables you want private to one thread
pthread_t
pthread_create( , , pf, (void *) argument)
pthread_self
pthread_detach( myid )
exit() kills the whole precess,
pthread_exit or return from (*pf)(..)
terminates the thread executing it
How Virtual memory is used for threads
Reentrant procedures.
Do not use static variables, so independently called
activations of the procedure do not interfere.
Using mutexs
Allocation and initialization:
pthread_mutex_t mp; or pmp = new( pthread_mutex_t );
pthread_mutex_init(&mp, NULL);
or pthread_mutex_init(pmp, NULL);
Allocation and initialization are done only once!
pthread_mutex_lock( &mp );
or pthread_mutex_lock( pmp );
BLOCKS current thread if mutex mp is locked
Returns when some other thread unlocks mp.
//put the code to use protected data structures here
pthread_mutex_unlock(&mp);
Lecture 37 (5/5)
Demonstration of stepping through server and client
programs with gdb debugger in separate windows,
Where each process blocks
View process and socket tables with
ps -la and netstat -a
Concurrency: Multiple computations for which the time order
among the instructions of the different computations
is unpredictable.
(True) parallelism: Multiple computations that are really done
at the same time.
Scheduler: Part of the operating system that chooses which thread
or process to run now.
Lecture 38 (5/7)
Concurrency and parallelism definitions.
Time sharing.
System runs scheduler to decide what process or thread to
run next every time the CPU is interrupted by a clock tick
Clock ticks are generated by a timer clock,
typical tick period is 1/100 second
Processor modes: user and system (priviliged)
System instructions cause exceptions when processor is in system mode.
Examples of system instructions:
Instructions to change virtual memory mappings
syscall instructions
Instructions to change processor mode
Exception action:
1. Make mode become priviliged
2. Save PC in a fixed place
3. PC = fixed value (should be address of kernel's
interrupt processing routine)
4. Set register bit so software can determine exception's cause
Causes:
Timer
(Operating system runs the scheduler)
Scheduler decides chooses which process/thread to run now
syscall instruction
used to call for operating system services
Examples: open, read, write, socket, fork, exec, exit
Counting Semaphores
Used to control concurrent access to resources
used in producer-consumer situations
Model: Shared "toybox"
wait(S) [aka P(s), down(S), TAKE(S)]
{block until S > 0, then S=S-1}
(sleep until at least one toy appears, then
take it)
signal(S) [aka V(S), up(S) GIVE(S)]
{S=S+1; alert other processes to check S}
(put a toy in the box)
Lecture 39 (5/10)
Java
Compile once, execute everywhere
sam.java (source file), sam.class (object file), javac
Java Virtual Machine Language Specification
From www.javasoft.com
Running java programs
java (application runner)
Web browser, applet viewer (applet)
Fully qualified class names
Java design goals
Small (static) program size
.class file contains "bytecodes"
Stack oriented machine language
Demo of disassembled sample program
Sample
Dynamic Linking
Classes can be loaded via the Internet
Security
try to run untrusted applets "safely"
Units of Modularization
Package (hierarchical package name, eg
EDU.albany.csi402.java.
Class (like C++ classes)
Fully qualified class name is
package name.class-name
Virtual functions (as in C++)
An instance of a class with no virtual functions
only has data members.
An instance of a class with virtual functions
(has in addition to any data members)
a pointer to a
virtual function table
class wide
contains function pointers to bodies
of functions
Different function bodies
can be called for different instances.
All Java functions are virtual
Lecture 40 (5/12)
Exam Topics:
Java Intro, Java versus C++
Concurrency, scheduler, mutexs, threads, processes
System calls, what operating systems do, timesharing/multitasking
Client-Server applications using socket interface, read/write functions
Application message protocols
Assembling, relocation, linking, symbol tables
Beck sections 2.1 and 2.2
Beck section 3.2, Beck problem 16 of section 3.2 (on sections)
Applications of dictionaries
Virtual Memory: Address Translation, page alignment
Reading and interpreting an "unformatted" or "binary" such as ELF
Decoding and executing MIPS instructions, MIPS memory references,
delayed branches, intro to pipelining
C++ storage extents, use of the stack, free-store, data segment,
pointers and strings
Unix technicalities
PATH environment variable, absolute and relative pathnames
process list (ps command), socket list (netstat command)
job control (background, foreground, C-Z, C-C)
Make algorithm
Arithmetic: Overflow, sign extension, big and little endian
Java continued
Java class
one structure type, could be empty
some INSTANCE functions
some CLASS functions
some CLASS variables or constants
Every function must belong to a class
Class sources compiled into .class files
loaded and executed by Java Virtual Machine (JVM)
JVM Language
"byte coded"
stack oriented, small code size
JVM storage areas
Threads
Each thread has a PC and stack of frames
Each frame has local vars and an operand stack
Heap
Stores instances, like C/C++ free store
Method Area
Stores classes, like the code segment
Java types of variables
Primative: byte, short, char, int, long, float, double
Standardized
Reference: null or point to a class instance
C/C++, not Java have object (structure) variables
C/C++ = does copying of structures, copy operator can be
customized by the programmer, is complicated
Java, not C++, StringDict MyDict = new StringDict(..);
Reference assignment copies pointers, not objects.
Every non-primative is a pointer; the word pointer is eliminated
No "delete/free" operation; the heap is garbage collected
How an object reference is implemented in Sun's implementation
Handle, virtual function table, pointer to object data in heap
The invokevirtual instruction and how it calls a function
Caller has complete symbolic information about the function called
A reference to the instance FOR WHICH the function is called
should be in the stack and is passed to the called function.
Called Classes can be resolved in different ways by ClassLoaders,
including retrieval on the Internet.
