Inside Macintosh: Memory /

Chapter 1 - Introduction to Memory Management

This chapter is a general introduction to memory management on Macintosh computers. It describes how the Operating System organizes and manages the available memory, and it shows how you can use the services provided by the Memory Manager and other system software components to manage the memory in your application partition effectively.

You should read this chapter if your application or other software allocates memory dynamically during its execution. This chapter describes how to

• set up your application partition at launch time
• determine the amount of free memory in your application heap
• allocate and dispose of blocks of memory in your application heap
• minimize fragmentation in your application heap caused by blocks of memory that cannot move
• implement a scheme to avoid low-memory conditions

You should be able to accomplish most of your application's memory allocation and management by following the instructions given in this chapter. If, however, your application needs to allocate memory outside its own partition (for instance, in the system heap), you need to read the chapter "Memory Manager" in this book. If your application has timing-critical requirements or installs procedures that execute at interrupt time, you need to read the chapter "Virtual Memory Manager" in this book. If your application's executable code is divided into multiple segments, you might also want to look at the chapter "Segment Manager" in Inside Macintosh: Processes for guidelines on how to divide your code into segments. If your application uses resources, you need to read the chapter "Resource Manager" in Inside Macintosh: More Macintosh Toolbox for information on managing memory allocated to resources.

This chapter begins with a description of how the Macintosh Operating System organizes the available physical random-access memory (RAM) in a Macintosh computer and how it allocates memory to open applications. Then this chapter describes in detail how the Memory Manager allocates blocks of memory in your application's heap and how to use the routines provided by the Memory Manager to perform the memory-management tasks listed above.

This chapter ends with descriptions of the routines used to perform these tasks. The "Memory Management Reference" and "Summary of Memory Management" sections
in this chapter are subsets of the corresponding sections in the remaining chapters in
this book.

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Chapter Contents

About Memory

Organization of Memory by the Operating System

The System Heap

The System Global Variables

Organization of Memory in an Application Partition

The Application Stack

The Application Heap

The Application Global Variables and A5 World

Temporary Memory

Virtual Memory

Addressing Modes

Heap Management

Relocatable and Nonrelocatable Blocks

Properties of Relocatable Blocks

Locking and Unlocking Relocatable Blocks

Purging and Reallocating Relocatable Blocks

Memory Reservation

Heap Purging and Compaction

Heap Fragmentation

Deallocating Nonrelocatable Blocks

Reserving Memory

Locking Relocatable Blocks

Allocating Nonrelocatable Blocks

Summary of Preventing Fragmentation

Dangling Pointers

Compiler Dereferencing

Loading Code Segments

Callback Routines

Invalid Handles

Disposed Handles

Empty Handles

Fake Handles

Low-Memory Conditions

Memory Cushions

Memory Reserves

Grow-Zone Functions

Using Memory

Setting Up the Application Heap

Changing the Size of the Stack

Expanding the Heap

Allocating Master Pointer Blocks

Determining the Amount of Free Memory

Allocating Blocks of Memory

Maintaining a Memory Reserve

Defining a Grow-Zone Function

Memory Management Reference

Memory Management Routines

Setting Up the Application Heap

Allocating and Releasing Relocatable Blocks of Memory

Allocating and Releasing Nonrelocatable Blocks of Memory

Setting the Properties of Relocatable Blocks

Managing Relocatable Blocks

Manipulating Blocks of Memory

Assessing Memory Conditions

Grow-Zone Operations

Setting and Restoring the A5 Register

Application-Defined Routines

Grow-Zone Functions

Summary of Memory Management

Pascal Summary

Data Types

Memory Management Routines

Application-Defined Routines

C Summary

Data Types

Memory Management Routines

Application-Defined Routines

Assembly-Language Summary

Global Variables

Result Codes