An atomic operation is an operation that can only be done once at a certain "tick" time, eventhough another same operation is simultaneously performed by another thread on another CPU core.
For example
Code:
mkdir /home/flag
is an atomic operation (without the -p option)
so that even if you submit it many time
if I rename a dir
mv dir dir2
Is this operation atomic? Suppose there 100 files in dir, does linux rename them one by one or at once?
In other words, is there a time at which both dir and dir2 exist, with dir has, say 30 files and dir2 has the rest 70 files? (4 Replies)
Hello,
I need to implement a locking system in C. My problem is how to make the check if the lock file exist and locking it atomic operation.
I want to make something like this:
FILE* lock_fname;
lock_fname = fopen ( "file.lock", "r");
/*check if file exsists*/
if (lock_fname)
{
fclose... (7 Replies)
hi guys.
can we use fread and fwrite with pipes to write data more than PIPE_BUF atomically since they lock FILE object until I/O operation finish? (1 Reply)
Are system calls atomic operations?
Is a system call can be interrupted? (2 Replies)
Discussion started by: vistastar
2 Replies
LEARN ABOUT SUNOS
atomic_ops
atomic_ops(9F)atomic_ops(9F)NAME
atomic_ops - atomic operations
SYNOPSIS
#include <sys/atomic.h>
This collection of functions provides atomic memory operations. There are 8 different classes of atomic operations:
atomic_add(9F) These functions provide an atomic addition of a signed value to a variable.
atomic_and(9F) These functions provide an atomic logical 'and' of a value to a variable.
atomic_bits(9F) These functions provide atomic bit setting and clearing within a variable.
atomic_cas(9F) These functions provide an atomic comparison of a value with a variable. If the comparison is equal, then swap in a new
value for the variable, returning the old value of the variable in either case.
atomic_dec(9F) These functions provide an atomic decrement on a variable.
atomic_inc(9F) These functions provide an atomic increment on a variable.
atomic_or(9F) These functions provide an atomic logical 'or' of a value to a variable.
atomic_swap(9F) These functions provide an atomic swap of a value with a variable, returning the old value of the variable.
See attributes(5) for descriptions of the following attributes:
+-----------------------------+-----------------------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+-----------------------------+-----------------------------+
|Interface Stability |Evolving |
+-----------------------------+-----------------------------+
atomic_add(9F), atomic_and(9F), atomic_bits(9F), atomic_cas(9F), atomic_dec(9F), atomic_inc(9F), atomic_or(9F), atomic_swap(9F), mem-
bar_ops(9F), attributes(5)
Atomic instructions ensure global visibility of atomically-modified variables on completion. In a relaxed store order system, this does
not guarantee that the visibility of other variables will be synchronized with the completion of the atomic instruction. If such synchro-
nization is required, memory barrier instructions must be used. See membar_ops(9F).
Atomic instructions can be expensive. since they require synchronization to occur at a hardware level. This means they should be used with
care to ensure that forcing hardware level synchronization occurs a minimum number of times. For example, if you have several variables
that need to be incremented as a group, and each needs to be done atomically, then do so with a mutex lock protecting all of them being
incremented rather than using the atomic_inc(9F) operation on each of them.
28 Mar 2005 atomic_ops(9F)
10-29-2012
