Motorola MCP750 Specifications download pdf (Page 137)

Understanding the Kernel Environmen

9-1

Synchronization Routines 9

The kernel provides three broad categories of synchronization/serialization routines: spin

locks, sleep locks, and event synchronization primitives. These routines are used to main-

tain data integrity in the system by serializing process access to shared resources and by

synchronizing processes. The routines associated with each category are presented in the

sections that follow. Guidelines for using these routines are provided in Chapter 11 (“Mul-

tithreading a Device Driver”).

Spin Locks 9

Spin locks are low-level, busy-waiting primitives. They are used to serialize access to

shared resources when blocking primitives cannot be used (at interrupt level, for example)

and when the expected wait time is very short. Spin locks are of two types: basic spin

locks and read/write spin locks.

Basic locks allow only one process to gain access to a shared resource at a time. The basic

lock routines are as follows:

LOCK(D3) Acquire a basic lock

LOCK_ALLOC(D3) Allocate and initialize a basic lock

LOCK_DEALLOC(D3) Deallocate an instance of a basic lock

TRYLOCK(D3) Try to acquire a basic lock

UNLOCK(D3) Release a basic lock

Read/write locks allow you to distinguish between readers and writers when controlling

access to shared resources. Multiple processes can simultaneously obtain a lock in read

mode. Only one process can obtain a lock in write mode. A lock is available in read mode

if it is idle or it is held by one or more readers and there are no waiting writers. A lock is

available in write mode only if it is idle.

The read/write lock routines are as follows:

RW_ALLOC(D3) Allocate and initialize a read/write lock

RW_DEALLOC(D3) Deallocate an instance of a read/write lock

RW_RDLOCK(D3) Acquire a read/write lock in read mode

RW_WRLOCK(D3) Acquire a read/write lock in write mode

RW_TRYRDLOCK(D3) Try to acquire a read/write lock in read mode

RW_TRYWRLOCK(D3) Try to acquire a read/write lock in write mode

RW_UNLOCK(D3) Release a read/write lock

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Motorola MCP750 Specifications Page 137