How to know if a function will be called for the last time
I'm working on a self-made malloc(), realloc() and free() for a school project.
I would like to know if there is a way for my function free() to know if it's his last call in the program.
Edit : I don't have main() under control, it's for a library.
I would like to use sbrk() to free just one time at the end, because for now i'm calling it after all free() and it's not optimised.
(I deleted the piece of code because i don't want to be strike by my school)
Seems that it's not possible.. Thanks for your reply.
c
asked Nov 15 '18 at 12:25
William ChoukrounWilliam Choukroun
11
|
show 8 more comments
I'm working on a self-made malloc(), realloc() and free() for a school project.
I would like to know if there is a way for my function free() to know if it's his last call in the program.
Edit : I don't have main() under control, it's for a library.
I would like to use sbrk() to free just one time at the end, because for now i'm calling it after all free() and it's not optimised.
(I deleted the piece of code because i don't want to be strike by my school)
Seems that it's not possible.. Thanks for your reply.
c
asked Nov 15 '18 at 12:25
William ChoukrounWilliam Choukroun
11
5
What are you trying to achieve with that knowledge?
– Fildor
Nov 15 '18 at 12:26
4
Sounds equivalent to the Halting Problem.
– aschepler
Nov 15 '18 at 12:28
2
Not really sure what you're asking, or why you'd need to know that. Do you mean that if you havefree(); if(rand()%2) free();the firstfree()should somehow know if the second one will be called or not?
– JJJ
Nov 15 '18 at 12:31
1
Knowing the "last potential call" is practically worthless – either the cleanup code will sometimes not be called, which leads to bugs that are hard to debug, or if it doesn't matter if the cleanup code is sometimes not called, why include it at all?
– JJJ
Nov 15 '18 at 12:43
1
@JJJ Even worse, what if the "last call" isn't? For example, anexit()handler registered withatexit()callsfree()after the supposed-to-be "last" call.
– Andrew Henle
Nov 15 '18 at 12:48
|
show 8 more comments
I'm working on a self-made malloc(), realloc() and free() for a school project.
I would like to know if there is a way for my function free() to know if it's his last call in the program.
Edit : I don't have main() under control, it's for a library.
I would like to use sbrk() to free just one time at the end, because for now i'm calling it after all free() and it's not optimised.
(I deleted the piece of code because i don't want to be strike by my school)
Seems that it's not possible.. Thanks for your reply.
c
asked Nov 15 '18 at 12:25
William ChoukrounWilliam Choukroun
11
I'm working on a self-made malloc(), realloc() and free() for a school project.
I would like to know if there is a way for my function free() to know if it's his last call in the program.
Edit : I don't have main() under control, it's for a library.
I would like to use sbrk() to free just one time at the end, because for now i'm calling it after all free() and it's not optimised.
(I deleted the piece of code because i don't want to be strike by my school)
Seems that it's not possible.. Thanks for your reply.
c
c
asked Nov 15 '18 at 12:25
William ChoukrounWilliam Choukroun
11
asked Nov 15 '18 at 12:25
William ChoukrounWilliam Choukroun
11
edited Nov 15 '18 at 12:50
William Choukroun
asked Nov 15 '18 at 12:25
William ChoukrounWilliam Choukroun
11
asked Nov 15 '18 at 12:25
William ChoukrounWilliam Choukroun
11
asked Nov 15 '18 at 12:25
William ChoukrounWilliam Choukroun
11
11
5
What are you trying to achieve with that knowledge?
– Fildor
Nov 15 '18 at 12:26
4
Sounds equivalent to the Halting Problem.
– aschepler
Nov 15 '18 at 12:28
2
Not really sure what you're asking, or why you'd need to know that. Do you mean that if you havefree(); if(rand()%2) free();the firstfree()should somehow know if the second one will be called or not?
– JJJ
Nov 15 '18 at 12:31
1
Knowing the "last potential call" is practically worthless – either the cleanup code will sometimes not be called, which leads to bugs that are hard to debug, or if it doesn't matter if the cleanup code is sometimes not called, why include it at all?
– JJJ
Nov 15 '18 at 12:43
1
@JJJ Even worse, what if the "last call" isn't? For example, anexit()handler registered withatexit()callsfree()after the supposed-to-be "last" call.
– Andrew Henle
Nov 15 '18 at 12:48
|
show 8 more comments
5
What are you trying to achieve with that knowledge?
– Fildor
Nov 15 '18 at 12:26
4
Sounds equivalent to the Halting Problem.
– aschepler
Nov 15 '18 at 12:28
2
Not really sure what you're asking, or why you'd need to know that. Do you mean that if you havefree(); if(rand()%2) free();the firstfree()should somehow know if the second one will be called or not?
– JJJ
Nov 15 '18 at 12:31
1
Knowing the "last potential call" is practically worthless – either the cleanup code will sometimes not be called, which leads to bugs that are hard to debug, or if it doesn't matter if the cleanup code is sometimes not called, why include it at all?
– JJJ
Nov 15 '18 at 12:43
1
@JJJ Even worse, what if the "last call" isn't? For example, anexit()handler registered withatexit()callsfree()after the supposed-to-be "last" call.
– Andrew Henle
Nov 15 '18 at 12:48
5
5
What are you trying to achieve with that knowledge?
– Fildor
Nov 15 '18 at 12:26
What are you trying to achieve with that knowledge?
– Fildor
Nov 15 '18 at 12:26
4
4
Sounds equivalent to the Halting Problem.
– aschepler
Nov 15 '18 at 12:28
Sounds equivalent to the Halting Problem.
– aschepler
Nov 15 '18 at 12:28
2
2
Not really sure what you're asking, or why you'd need to know that. Do you mean that if you have
free(); if(rand()%2) free(); the first free() should somehow know if the second one will be called or not?– JJJ
Nov 15 '18 at 12:31
Not really sure what you're asking, or why you'd need to know that. Do you mean that if you have
free(); if(rand()%2) free(); the first free() should somehow know if the second one will be called or not?– JJJ
Nov 15 '18 at 12:31
1
1
Knowing the "last potential call" is practically worthless – either the cleanup code will sometimes not be called, which leads to bugs that are hard to debug, or if it doesn't matter if the cleanup code is sometimes not called, why include it at all?
– JJJ
Nov 15 '18 at 12:43
Knowing the "last potential call" is practically worthless – either the cleanup code will sometimes not be called, which leads to bugs that are hard to debug, or if it doesn't matter if the cleanup code is sometimes not called, why include it at all?
– JJJ
Nov 15 '18 at 12:43
1
1
@JJJ Even worse, what if the "last call" isn't? For example, an
exit() handler registered with atexit() calls free() after the supposed-to-be "last" call.– Andrew Henle
Nov 15 '18 at 12:48
@JJJ Even worse, what if the "last call" isn't? For example, an
exit() handler registered with atexit() calls free() after the supposed-to-be "last" call.– Andrew Henle
Nov 15 '18 at 12:48
|
show 8 more comments
3 Answers
3
active
oldest
votes
No, there is, in general, no way to know whether a function is being called for the last time in a program execution.
A program could be designed to convey this knowledge, by passing an argument indicating it. You would have to build this into all functions in the call chain. Even so, it may cause some code to be awkward, as the last iterations of some loops may need special treatment.
Generally, it is preferable to call separate clean-up code at suitable times rather than trying to incorporate it automatically into routine operations in the way you seem to be attempting.
answered Nov 15 '18 at 12:35
Eric PostpischilEric Postpischil
78.2k883166
add a comment |
No you cannot.
Example :
- A GUI will call your function every time the user clicks "ok".
- There is no way for the program to known if the user will click again or switch-off the computer after a click.
A little joke:
The only possiblity for you, to achieve what you want, is have your function free() abort the whole program, so that you are sure it will not be called again.
answered Nov 15 '18 at 12:38
user803422user803422
9472623
add a comment |
No, it's not possible, as other answers have stated.
The closest thing you can do is register an atexit handler to perform whatever cleanup you want to do:
static int init = 0;
void cleanup()
{
// last call to sbrk to clean up
}
void *my_malloc(size_t size)
{
if (!init) {
init = 1;
atexit(cleanup);
}
...
}
answered Nov 15 '18 at 12:57
dbushdbush
101k13105142
add a comment |
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3 Answers
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active
oldest
votes
3 Answers
3
active
oldest
votes
active
oldest
votes
active
oldest
votes
No, there is, in general, no way to know whether a function is being called for the last time in a program execution.
A program could be designed to convey this knowledge, by passing an argument indicating it. You would have to build this into all functions in the call chain. Even so, it may cause some code to be awkward, as the last iterations of some loops may need special treatment.
Generally, it is preferable to call separate clean-up code at suitable times rather than trying to incorporate it automatically into routine operations in the way you seem to be attempting.
answered Nov 15 '18 at 12:35
Eric PostpischilEric Postpischil
78.2k883166
add a comment |
No, there is, in general, no way to know whether a function is being called for the last time in a program execution.
A program could be designed to convey this knowledge, by passing an argument indicating it. You would have to build this into all functions in the call chain. Even so, it may cause some code to be awkward, as the last iterations of some loops may need special treatment.
Generally, it is preferable to call separate clean-up code at suitable times rather than trying to incorporate it automatically into routine operations in the way you seem to be attempting.
answered Nov 15 '18 at 12:35
Eric PostpischilEric Postpischil
78.2k883166
add a comment |
No, there is, in general, no way to know whether a function is being called for the last time in a program execution.
A program could be designed to convey this knowledge, by passing an argument indicating it. You would have to build this into all functions in the call chain. Even so, it may cause some code to be awkward, as the last iterations of some loops may need special treatment.
Generally, it is preferable to call separate clean-up code at suitable times rather than trying to incorporate it automatically into routine operations in the way you seem to be attempting.
answered Nov 15 '18 at 12:35
Eric PostpischilEric Postpischil
78.2k883166
No, there is, in general, no way to know whether a function is being called for the last time in a program execution.
A program could be designed to convey this knowledge, by passing an argument indicating it. You would have to build this into all functions in the call chain. Even so, it may cause some code to be awkward, as the last iterations of some loops may need special treatment.
Generally, it is preferable to call separate clean-up code at suitable times rather than trying to incorporate it automatically into routine operations in the way you seem to be attempting.
answered Nov 15 '18 at 12:35
Eric PostpischilEric Postpischil
78.2k883166
answered Nov 15 '18 at 12:35
Eric PostpischilEric Postpischil
78.2k883166
answered Nov 15 '18 at 12:35
Eric PostpischilEric Postpischil
78.2k883166
answered Nov 15 '18 at 12:35
Eric PostpischilEric Postpischil
78.2k883166
78.2k883166
add a comment |
add a comment |
No you cannot.
Example :
- A GUI will call your function every time the user clicks "ok".
- There is no way for the program to known if the user will click again or switch-off the computer after a click.
A little joke:
The only possiblity for you, to achieve what you want, is have your function free() abort the whole program, so that you are sure it will not be called again.
answered Nov 15 '18 at 12:38
user803422user803422
9472623
add a comment |
No you cannot.
Example :
- A GUI will call your function every time the user clicks "ok".
- There is no way for the program to known if the user will click again or switch-off the computer after a click.
A little joke:
The only possiblity for you, to achieve what you want, is have your function free() abort the whole program, so that you are sure it will not be called again.
answered Nov 15 '18 at 12:38
user803422user803422
9472623
add a comment |
No you cannot.
Example :
- A GUI will call your function every time the user clicks "ok".
- There is no way for the program to known if the user will click again or switch-off the computer after a click.
A little joke:
The only possiblity for you, to achieve what you want, is have your function free() abort the whole program, so that you are sure it will not be called again.
answered Nov 15 '18 at 12:38
user803422user803422
9472623
No you cannot.
Example :
- A GUI will call your function every time the user clicks "ok".
- There is no way for the program to known if the user will click again or switch-off the computer after a click.
A little joke:
The only possiblity for you, to achieve what you want, is have your function free() abort the whole program, so that you are sure it will not be called again.
answered Nov 15 '18 at 12:38
user803422user803422
9472623
answered Nov 15 '18 at 12:38
user803422user803422
9472623
answered Nov 15 '18 at 12:38
user803422user803422
9472623
answered Nov 15 '18 at 12:38
user803422user803422
9472623
9472623
add a comment |
add a comment |
No, it's not possible, as other answers have stated.
The closest thing you can do is register an atexit handler to perform whatever cleanup you want to do:
static int init = 0;
void cleanup()
{
// last call to sbrk to clean up
}
void *my_malloc(size_t size)
{
if (!init) {
init = 1;
atexit(cleanup);
}
...
}
answered Nov 15 '18 at 12:57
dbushdbush
101k13105142
add a comment |
No, it's not possible, as other answers have stated.
The closest thing you can do is register an atexit handler to perform whatever cleanup you want to do:
static int init = 0;
void cleanup()
{
// last call to sbrk to clean up
}
void *my_malloc(size_t size)
{
if (!init) {
init = 1;
atexit(cleanup);
}
...
}
answered Nov 15 '18 at 12:57
dbushdbush
101k13105142
add a comment |
No, it's not possible, as other answers have stated.
The closest thing you can do is register an atexit handler to perform whatever cleanup you want to do:
static int init = 0;
void cleanup()
{
// last call to sbrk to clean up
}
void *my_malloc(size_t size)
{
if (!init) {
init = 1;
atexit(cleanup);
}
...
}
answered Nov 15 '18 at 12:57
dbushdbush
101k13105142
No, it's not possible, as other answers have stated.
The closest thing you can do is register an atexit handler to perform whatever cleanup you want to do:
static int init = 0;
void cleanup()
{
// last call to sbrk to clean up
}
void *my_malloc(size_t size)
{
if (!init) {
init = 1;
atexit(cleanup);
}
...
}
answered Nov 15 '18 at 12:57
dbushdbush
101k13105142
answered Nov 15 '18 at 12:57
dbushdbush
101k13105142
answered Nov 15 '18 at 12:57
dbushdbush
101k13105142
answered Nov 15 '18 at 12:57
dbushdbush
101k13105142
101k13105142
add a comment |
add a comment |
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5
What are you trying to achieve with that knowledge?
– Fildor
Nov 15 '18 at 12:26
4
Sounds equivalent to the Halting Problem.
– aschepler
Nov 15 '18 at 12:28
2
Not really sure what you're asking, or why you'd need to know that. Do you mean that if you have
free(); if(rand()%2) free();the firstfree()should somehow know if the second one will be called or not?– JJJ
Nov 15 '18 at 12:31
1
Knowing the "last potential call" is practically worthless – either the cleanup code will sometimes not be called, which leads to bugs that are hard to debug, or if it doesn't matter if the cleanup code is sometimes not called, why include it at all?
– JJJ
Nov 15 '18 at 12:43
1
@JJJ Even worse, what if the "last call" isn't? For example, an
exit()handler registered withatexit()callsfree()after the supposed-to-be "last" call.– Andrew Henle
Nov 15 '18 at 12:48