Thread safe with CAS (atomic_comapre_and_set) in embedded system
I am trying to use CAS to perform thread safe in an embedded system.
Unfortunatly, it fails to work properly.
Say there is a global array and several threads will access it.
typedef struct{
int in_use;
data_type data;
} item_type;
item_type global_array[N]
The idea is: threads could use available item in the global_array which indicated by "in_use" flag. the implementation as below:
item_type* get_available_item_pointer(void){
int available_index = N;
for (int i=0; i<N; i++){
if (atomic_compare_and_set(&(global_array[index].in_use), FALSE, TRUE))
{
available_index = i;
break;
}
}
return &(global_array[index]);
}
void free_item_pointer(item_type* item_ptr){
if (item_ptr->in_use){
memset(&item_ptr->data, 0x0, sizeof(data_type));
item_ptr->in_use = FALSE; //should I use atomic function for this line?
}
}
In bad case, I find 2 threads happen to access same item and have data corruption, I have no idea why it is possible?
thread A is calling get_available_item_pointer() //return index 0
thread B is calling free_item_pointer() //freeing index 0
BTW, the atomic_compare_and_set implementation is like:
static inline int atomic_compare_and_set(
unsigned int* target,
unsigned int old_val,
unsigned int new_val)
{
unsigned int current_val;
__asm__ __volatile__(
......
return current_val == old_val;
}
multithreading thread-safety cas
asked Nov 26 '18 at 3:23
云海帆云海帆
11
add a comment |
I am trying to use CAS to perform thread safe in an embedded system.
Unfortunatly, it fails to work properly.
Say there is a global array and several threads will access it.
typedef struct{
int in_use;
data_type data;
} item_type;
item_type global_array[N]
The idea is: threads could use available item in the global_array which indicated by "in_use" flag. the implementation as below:
item_type* get_available_item_pointer(void){
int available_index = N;
for (int i=0; i<N; i++){
if (atomic_compare_and_set(&(global_array[index].in_use), FALSE, TRUE))
{
available_index = i;
break;
}
}
return &(global_array[index]);
}
void free_item_pointer(item_type* item_ptr){
if (item_ptr->in_use){
memset(&item_ptr->data, 0x0, sizeof(data_type));
item_ptr->in_use = FALSE; //should I use atomic function for this line?
}
}
In bad case, I find 2 threads happen to access same item and have data corruption, I have no idea why it is possible?
thread A is calling get_available_item_pointer() //return index 0
thread B is calling free_item_pointer() //freeing index 0
BTW, the atomic_compare_and_set implementation is like:
static inline int atomic_compare_and_set(
unsigned int* target,
unsigned int old_val,
unsigned int new_val)
{
unsigned int current_val;
__asm__ __volatile__(
......
return current_val == old_val;
}
multithreading thread-safety cas
asked Nov 26 '18 at 3:23
云海帆云海帆
11
Without knowing the memory visibility rules for your platform, I'm not sure how we could know what you need to do differently. You're not using anything portable (for memory visibility).
– David Schwartz
Nov 26 '18 at 4:35
add a comment |
I am trying to use CAS to perform thread safe in an embedded system.
Unfortunatly, it fails to work properly.
Say there is a global array and several threads will access it.
typedef struct{
int in_use;
data_type data;
} item_type;
item_type global_array[N]
The idea is: threads could use available item in the global_array which indicated by "in_use" flag. the implementation as below:
item_type* get_available_item_pointer(void){
int available_index = N;
for (int i=0; i<N; i++){
if (atomic_compare_and_set(&(global_array[index].in_use), FALSE, TRUE))
{
available_index = i;
break;
}
}
return &(global_array[index]);
}
void free_item_pointer(item_type* item_ptr){
if (item_ptr->in_use){
memset(&item_ptr->data, 0x0, sizeof(data_type));
item_ptr->in_use = FALSE; //should I use atomic function for this line?
}
}
In bad case, I find 2 threads happen to access same item and have data corruption, I have no idea why it is possible?
thread A is calling get_available_item_pointer() //return index 0
thread B is calling free_item_pointer() //freeing index 0
BTW, the atomic_compare_and_set implementation is like:
static inline int atomic_compare_and_set(
unsigned int* target,
unsigned int old_val,
unsigned int new_val)
{
unsigned int current_val;
__asm__ __volatile__(
......
return current_val == old_val;
}
multithreading thread-safety cas
asked Nov 26 '18 at 3:23
云海帆云海帆
11
I am trying to use CAS to perform thread safe in an embedded system.
Unfortunatly, it fails to work properly.
Say there is a global array and several threads will access it.
typedef struct{
int in_use;
data_type data;
} item_type;
item_type global_array[N]
The idea is: threads could use available item in the global_array which indicated by "in_use" flag. the implementation as below:
item_type* get_available_item_pointer(void){
int available_index = N;
for (int i=0; i<N; i++){
if (atomic_compare_and_set(&(global_array[index].in_use), FALSE, TRUE))
{
available_index = i;
break;
}
}
return &(global_array[index]);
}
void free_item_pointer(item_type* item_ptr){
if (item_ptr->in_use){
memset(&item_ptr->data, 0x0, sizeof(data_type));
item_ptr->in_use = FALSE; //should I use atomic function for this line?
}
}
In bad case, I find 2 threads happen to access same item and have data corruption, I have no idea why it is possible?
thread A is calling get_available_item_pointer() //return index 0
thread B is calling free_item_pointer() //freeing index 0
BTW, the atomic_compare_and_set implementation is like:
static inline int atomic_compare_and_set(
unsigned int* target,
unsigned int old_val,
unsigned int new_val)
{
unsigned int current_val;
__asm__ __volatile__(
......
return current_val == old_val;
}
multithreading thread-safety cas
multithreading thread-safety cas
asked Nov 26 '18 at 3:23
云海帆云海帆
11
asked Nov 26 '18 at 3:23
云海帆云海帆
11
edited Nov 26 '18 at 4:26
云海帆
asked Nov 26 '18 at 3:23
云海帆云海帆
11
asked Nov 26 '18 at 3:23
云海帆云海帆
11
asked Nov 26 '18 at 3:23
云海帆云海帆
11
11
Without knowing the memory visibility rules for your platform, I'm not sure how we could know what you need to do differently. You're not using anything portable (for memory visibility).
– David Schwartz
Nov 26 '18 at 4:35
add a comment |
Without knowing the memory visibility rules for your platform, I'm not sure how we could know what you need to do differently. You're not using anything portable (for memory visibility).
– David Schwartz
Nov 26 '18 at 4:35
Without knowing the memory visibility rules for your platform, I'm not sure how we could know what you need to do differently. You're not using anything portable (for memory visibility).
– David Schwartz
Nov 26 '18 at 4:35
Without knowing the memory visibility rules for your platform, I'm not sure how we could know what you need to do differently. You're not using anything portable (for memory visibility).
– David Schwartz
Nov 26 '18 at 4:35
add a comment |
0
active
oldest
votes
Your Answer
StackExchange.ifUsing("editor", function () {
StackExchange.using("externalEditor", function () {
StackExchange.using("snippets", function () {
StackExchange.snippets.init();
});
});
}, "code-snippets");
StackExchange.ready(function() {
var channelOptions = {
tags: "".split(" "),
id: "1"
};
initTagRenderer("".split(" "), "".split(" "), channelOptions);
StackExchange.using("externalEditor", function() {
// Have to fire editor after snippets, if snippets enabled
if (StackExchange.settings.snippets.snippetsEnabled) {
StackExchange.using("snippets", function() {
createEditor();
});
}
else {
createEditor();
}
});
function createEditor() {
StackExchange.prepareEditor({
heartbeatType: 'answer',
autoActivateHeartbeat: false,
convertImagesToLinks: true,
noModals: true,
showLowRepImageUploadWarning: true,
reputationToPostImages: 10,
bindNavPrevention: true,
postfix: "",
imageUploader: {
brandingHtml: "Powered by u003ca class="icon-imgur-white" href="https://imgur.com/"u003eu003c/au003e",
contentPolicyHtml: "User contributions licensed under u003ca href="https://creativecommons.org/licenses/by-sa/3.0/"u003ecc by-sa 3.0 with attribution requiredu003c/au003e u003ca href="https://stackoverflow.com/legal/content-policy"u003e(content policy)u003c/au003e",
allowUrls: true
},
onDemand: true,
discardSelector: ".discard-answer"
,immediatelyShowMarkdownHelp:true
});
}
});
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
StackExchange.ready(
function () {
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fstackoverflow.com%2fquestions%2f53474398%2fthread-safe-with-cas-atomic-comapre-and-set-in-embedded-system%23new-answer', 'question_page');
}
);
Post as a guest
Required, but never shown
0
active
oldest
votes
0
active
oldest
votes
active
oldest
votes
active
oldest
votes
Thanks for contributing an answer to Stack Overflow!
- Please be sure to answer the question. Provide details and share your research!
But avoid …
- Asking for help, clarification, or responding to other answers.
- Making statements based on opinion; back them up with references or personal experience.
To learn more, see our tips on writing great answers.
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
StackExchange.ready(
function () {
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fstackoverflow.com%2fquestions%2f53474398%2fthread-safe-with-cas-atomic-comapre-and-set-in-embedded-system%23new-answer', 'question_page');
}
);
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Without knowing the memory visibility rules for your platform, I'm not sure how we could know what you need to do differently. You're not using anything portable (for memory visibility).
– David Schwartz
Nov 26 '18 at 4:35