Synchronization methods

This document is a draft.

1 Atomic Integet Operations

As the name says, it provides instructions the execute atomically over integers, in other words, without any interruption. The atomic_t type is defined in inlcude/linux/types.h

The table bellow lists the Atomic Integer Methods:

Atomic Integer Operation	Description
ATOMIC_INIT(int i)	At declaration, initialize to i.
int atomic_read(atomic_t *v)	Atomically read the integer value of v.
void atomic_set(atomic_t *v, int i)	Atomically set v equal to i.
void atomic_add(int i, atomic_t *v)	Atomically add i to v.
void atomic_sub(int i, atomic_t *v)	Atomically subtract i from v.
void atomic_inc(atomic_t *v)	Atomically add one to v.
void atomic_dec(atomic_t *v)	Atomically subtract one from v.
int atomic_sub_and_test(int i, atomic_t *v)	Atomically subtract i from v and return true if the result is zero; otherwise false.
int atomic_add_negative(int i, atomic_t *v)	Atomically add i to v and return true if the result is negative; otherwise false.
int atomic_add_return(int i, atomic_t *v)	Atomically add i to v and return the result.
int atomic_sub_return(int i, atomic_t *v)	Atomically subtract i from v and return the result.
int atomic_inc_return(int i, atomic_t *v)	Atomically increment v by one and return the result.
int atomic_dec_return(int i, atomic_t *v)	Atomically decrement v by one and return the result.
int atomic_dec_and_test(atomic_t *v)	Atomically decrement v by one and return true if zero; false otherwise.
int atomic_inc_and_test(atomic_t *v)	Atomically increment v by one and return true if the result is zero; false otherwise.

Theses methos are define in include/asm-generic/atomic.h for 32 bit integers. In include/asm-generic/atomic64.h one can find a 64 bit generic implementation, that can be used in 32 bit processors as well.

1.1 Atomic Bitwise Operations

2 Mutexes

3 Semaphores

Semaphores should be avoided in new code, instead use mutexes.

4 Spin Locks

5 RCU (Read-Copy Update)