Block Structure and Non-Block Structure Storage Allocation

Block Structure and Non-Block Structure Storage Allocation:

• Compiler must carry out the storage allocation and provide access to variables and data
• Allocation can be done in two ways:

Compiler Time Allocation or Static Storage Allocation

• A static storage allocation decision is taken by the compiler by looking only at the text of the program, but not by looking at what the program does when it executes
• Allocation is done at compile time

Runtime Allocation or Dynamic Storage Allocation

• A storage allocation decision is dynamic if it can be decided only while program is running
• Allocation is done at runtime 
• Storage allocation can be done for two types of data variable:

                Local data

                Non local data

• The local data can be handled using activation record where as non-local data can be handled using scope information
• The block structured storage allocation can be done using static scope
• The non-block structured allocation can be done using dynamic scope

Scope storage allocation includes,

• Definition of procedure
• Declaration of a name or variable
• Scope of declaration

Dynamic storage allocation includes,

• Activation of procedure
• Binding of a name
• Lifetime of a binding

Activation Record

• Information needed for each execution of a procedure is stored in a record called activation record
• Procedure calls and returns are usually managed by a runtime stack called the control stack
• Each live activation has an activation record or a frame
• The root of activation tree is a the bottom of the stack
• The current execution path specifies the content of the stack with the last activation as record in the top of the stack
• Activation record contains 7 fields which are:

Returned

Actual parameters

Control link

Access link

Machine status

Local data

Temporary data

• Size of each field of activation record can be estimated at compile time.

Temporary Values: 

• Temporary values are those arising from the evaluation of expressions, in case where those temporaries cannot be held in registers.

Local Data: 

• The local data is a data that is local to the execution of a procedure which is stored in activation record.

Machine Status: 

• It holds the information regarding the status of the machine just before the call to a procedure. It contains the machine registers and program counter.

Access Link:

• It is an optional link
• It locates data needed by the called procedure which is found somewhere else i.e., in another activation record
• It also known as static link field

Control Link:

• it is an optional link
• It points to the activation record of the calling procedure
• It is also known as dynamic link field

Actual Parameters:

• The parameters of a calling procedure are known as actual parameters
• Actual parameters are passed to the called procedure
• These values are not placed in the activation record but rather in registers

Return Values:

• Return values return the results from called procedure to calling procedure
• It is used to store the result of a function call

Note:

• Not all fields mentioned are used by all compilers or languages. Registers can take the place of one or more fields.
• Sizes of almost all fields can be determined at compile time. An execution arises when the procedure has a local array whose size is determined by the value of an actual parameter that is available only when the procedure is called at runtime

Example:

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About Data Sciences by Venu

Hi, My name is Venugopala Chary and I'm Currently working as Associate Professor in Reputed Engineerng College, Hyderabad. I have B.Tech and M.tech in regular from JNTU Hyderabad. I have 11 Years of Teaching Experience for both B.Tech and M.Tech Courses.