Language Processors (The Interpreter) System Programing

Language Processors

Introduction

1.Language processing activities arise due to the differences between the manner in which a software designer describes the ideas concerning the behavior of software and the manner in which these ideas are implemented in computer system.

 2.The designer expresses the ideas in terms related to the application domain of the software.

 3.To implement these ideas, their description has to be interpreted in terms related to the execution domain.

Semantic Gap

The term semantics to represent the rules of meaning of a domain, and the term semantic gap to represent difference between the semantics of two domains.
 

 
The semantic gap has many consequences, some of the important are

1. Large development times
2. Large development effort
3. Poor quality software.

Key Software engineering steps

1. Specification and design of an application program, followed by its coding in a programming language Execution of the program with the help of language processor
2. An Application program written in a programming language is governed by semantics of a programming language.
3. Thus use of programming language has introduces a new domain, programming language domain PL Domain.

 Specification and execution Gap

Difference between specification gap and execution gap

Specification Gap:

Semantic gap between two specification of the same task

Execution Gap:

Semantic gap between the semantics of programs that performs the same task but written in different programming languages.

Problem and procedure oriented programming languages

Problem oriented programming languages:
Lets a user specify a computation using data and operation that are meaningful in the area of the computation
 

Procedure oriented programming languages:

It provides some standard methods of creating data and performing operations and lets the user describe the intended computation by using them
 

 

Language Processors

•  A language processor is software which bridge a specification or execution gap.

 

Language processor abandons generation of target program if it detects error in the source program 

Different Types of Language Processors:

1. A Language Translator
2. De-translator
3. Preprocessor 
4. Language migrator

Language translator:

bridges an execution gap between PL, and the machine language of a computer. 

De-translator

Bridges the same execution gap as the language translator but in the opposite direction

  Preprocessor

  Bridges an execution gap but is not a language translator

  Language Migrator

  Bridges specification gap between two programming languages

Example: Preprocessor and Translator 

 

Interpreter

An interpreter is language processor which bridges an execution gap without generating a machine language program that means the execution gap vanishes totally.

Fundamental activities divided into those that bridge the specification gap and execution gap.

• Program generation activities
• Program execution activities

Program Generation:

1. A program generation activity aims at automatic generation of a program.
2. A source language is a specification language of an application domain and the target language is procedure oriented PL.
3. Program generator introduces a new domain between the application and PL domain, call this the program generator domain.
4. Specification gap now between Application domain and program generation domain, reduction in the specification gap increases the reliability of the generated program.

 

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There are 2 popular models of program execution

1.Program Translation
2.Program Interpretation

Lets us know briefly about these two,

Program Translation:The program translation model bridges the execution gap by translating a sources program into program in the machine or assembly language of the computer system, called target program. 







Characteristics of the program translation model:

1. A program must be translated before it can be executed
2. The translated program may be saved in a file. The saved program may be executed repeatedly.
3. A program must be retranslated following modifications.

 


Program Interpretation: during interpretation interpreter takes source program statement, determines its meaning and performs actions which implement it.


The function of an interpreter is same as the execution of machine language program by CPU.  

 Characteristics:

1. The source program is retained in the source form itself, no target program form exists,
2. A statement is analyzed during its interpretation.

 


 Comparison

1.  In translator whole program is translated into target and if modified the source program, whole source program is translated irrespective to size of modification.
2. That not the in case of interpreter, interpretation is slower than execution of m/c language program. 

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What is Deadlock? Defination of Deadlock in Operating System Pdf/ebook/ppt Download Free

What is Deadlock?

• System Model
• Deadlock Characterization
• Methods for Handling Deadlocks
• Deadlock Prevention
• Deadlock Avoidance
• Deadlock Detection
• Recovery from Deadlock
• Combined Approach to Deadlock Handling

A set of blocked processes each holding a resource and waiting to acquire a resource held by another process in the set.
Example
System has 2 tape drives.
P1 and P2 each hold one tape drive and each needs another one.
Example
semaphores A and B, initialized to 1

    P0           P1
wait (A);        wait(B)
wait (B);        wait(A)


Meaning of Deadlock

A set of blocked processes each holding a resource and waiting to acquire a resource held by another process in the set.

 Example
A system having 2 tape drives or cd drives.

Here is a ppt which contains everything related to Deadlock, images, examples, problems,

you can view the ppt directly without downloading it,

  
 Bridge Crossing Example

• Traffic only in one direction.
• Each section of a bridge can be viewed as a resource.
• If a deadlock occurs, it can be resolved if one car backs up (preempt resources and rollback).
• Several cars may have to be backed up if a deadlock occurs.
• Starvation is possible.

Resource types R1, R2, . . ., Rm
CPU cycles, memory space, I/O devices
Each resource type Ri has Wi instances.
Each process utilizes a resource as follows:

• request
• use
• release

Deadlock Characterization
Deadlock can arise if four conditions hold simultaneously.

Mutual exclusion:  only one process at a time can use a resource.
 
Hold and wait:  a process holding at least one resource is waiting to acquire additional resources held by other processes.
 
No preemption:  a resource can be released only voluntarily by the process holding it, after that process has completed its task.
 
Circular wait:  there exists a set {P0, P1, …, P0} of waiting processes such that 

P0 is waiting for a resource that is held by P1,
    P1 is waiting for a resource that is held by  P2, …,
    Pn–1 is waiting for a resource that is held by Pn,
    and P0 is waiting for a resource that is held by P0.

Resource-Allocation Graph
A set of vertices V and a set of edges E.






V is partitioned into two types:
P = {P1, P2, …, Pn}, the set consisting of all the processes in the system.
R = {R1, R2, …, Rm}, the set consisting of all resource types in the system.
request edge – directed edge P1 -> Rj
assignment edge – directed edge Rj ->  Pi


Basic Facts 
If graph contains no cycles -> no deadlock.
If graph contains a cycle
if only one instance per resource type, then deadlock.
if several instances per resource type, possibility of deadlock

Methods for Handling Deadlocks

1. Ensure that the system will never enter a deadlock state.
2. Allow the system to enter a deadlock state and then recover.
3. Ignore the problem and pretend that deadlocks never occur in the system; used by most operating systems, including UNIX.

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 Deadlock Prevention


Mutual Exclusion – not required for sharable resources; must hold for nonsharable resources.
 
Hold and Wait – must guarantee that whenever a process requests a resource, it does not hold any other resources.
 
Require process to request and be allocated all its resources before it begins execution, or allow process to request resources only when the process has none.
Low resource utilization; starvation possible.

No Preemption – If a process that is holding some resources requests another resource that cannot be immediately allocated to it, then all resources currently being held are released.
 
Preempted resources are added to the list of resources for which the process is waiting.
 
Process will be restarted only when it can regain its old resources, as well as the new ones that it is requesting.
 
Circular Wait – impose a total ordering of all resource types, and require that each process requests resources in an increasing order of enumeration

Deadlock Avoidance

Simplest and most useful model requires that each process declare the maximum number of resources of each type that it may need.
 
The deadlock-avoidance algorithm dynamically examines the resource-allocation state to ensure that there can never be a circular-wait condition.
 
Resource-allocation state is defined by the number of available and allocated resources, and the maximum demands of the processes.


Safe State

When a process requests an available resource, system must decide if immediate allocation leaves the system in a safe state.
System is in safe state if there exists a safe sequence of all processes.
Sequence <P1, P2, …, Pn> is safe if for each Pi, the resources that Pi can still request can be satisfied by currently available resources + resources held by all the Pj, with j<I.
If Pi resource needs are not immediately available, then Pi can wait until all Pj have finished.
When Pj is finished, Pi can obtain needed resources, execute, return allocated resources, and terminate.
When Pi terminates, Pi+1 can obtain its needed resources, and so on.
 
Basic Facts

If a system is in safe state  no deadlocks.
If a system is in unsafe state  possibility of deadlock.
Avoidance  ensure that a system will never enter an unsafe state.
 
 

 Resource-Allocation Graph Algorithm

Claim edge Pi => Rj indicated that process Pi may request resource Rj; represented by a dashed line.
 
Claim edge converts to request edge when a process requests a resource.
When a resource is released by a process, assignment edge reconverts to a claim edge.
Resources must be claimed a priori in the system.

Resource-Allocation Graph For Deadlock Avoidance

Deadlock Condition System Programming & Operating system pdf

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