Is this function re-entrant?

DNM_Manager.c

struct DNM_s

{

    uint32_t Addr;

    uint32_t SerialNum;

    uint32_t SubnetMask;

    uint16_t Tick;

    uint8_t Name[NAME_SIZE];

}DNMTemp;



pDNM DNMManager_New(void)    //reentrant?

{

    return &DNMTemp;

}

GeeksForGeeks says: To be reentrant, the function may not use global and static data.

I do use global data "DNMTemp" in this case. However, DNMTemp's value is not changed and function only return its address.

edited Jan 19 at 3:30

asked Jan 19 at 3:25

Andy Lin

517

3

This function is reentrant, but whatever you call it from probably isn't.

– Matt Timmermans
Jan 19 at 3:40

I don't understand it. Can you give me an example?

– Andy Lin
Jan 19 at 4:04

1

You are handing out the same pointer for every call, so everyone who calls it will be accessing the same object. Whatever function calls this one, it will probably use that pointer for something that could be messed up by a reentrant call to the same function.

– Matt Timmermans
Jan 19 at 4:17

What global data do you think it uses? It doesn't use the value of DNMTemp.

– David Schwartz
Jan 19 at 8:58

add a comment |

DNM_Manager.c

struct DNM_s

{

    uint32_t Addr;

    uint32_t SerialNum;

    uint32_t SubnetMask;

    uint16_t Tick;

    uint8_t Name[NAME_SIZE];

}DNMTemp;



pDNM DNMManager_New(void)    //reentrant?

{

    return &DNMTemp;

}

GeeksForGeeks says: To be reentrant, the function may not use global and static data.

I do use global data "DNMTemp" in this case. However, DNMTemp's value is not changed and function only return its address.

edited Jan 19 at 3:30

asked Jan 19 at 3:25

Andy Lin

517

3

This function is reentrant, but whatever you call it from probably isn't.

– Matt Timmermans
Jan 19 at 3:40

I don't understand it. Can you give me an example?

– Andy Lin
Jan 19 at 4:04

1

You are handing out the same pointer for every call, so everyone who calls it will be accessing the same object. Whatever function calls this one, it will probably use that pointer for something that could be messed up by a reentrant call to the same function.

– Matt Timmermans
Jan 19 at 4:17

What global data do you think it uses? It doesn't use the value of DNMTemp.

– David Schwartz
Jan 19 at 8:58

add a comment |

DNM_Manager.c

struct DNM_s

{

    uint32_t Addr;

    uint32_t SerialNum;

    uint32_t SubnetMask;

    uint16_t Tick;

    uint8_t Name[NAME_SIZE];

}DNMTemp;



pDNM DNMManager_New(void)    //reentrant?

{

    return &DNMTemp;

}

GeeksForGeeks says: To be reentrant, the function may not use global and static data.

I do use global data "DNMTemp" in this case. However, DNMTemp's value is not changed and function only return its address.

edited Jan 19 at 3:30

asked Jan 19 at 3:25

Andy Lin

517

DNM_Manager.c

struct DNM_s

{

    uint32_t Addr;

    uint32_t SerialNum;

    uint32_t SubnetMask;

    uint16_t Tick;

    uint8_t Name[NAME_SIZE];

}DNMTemp;



pDNM DNMManager_New(void)    //reentrant?

{

    return &DNMTemp;

}

GeeksForGeeks says: To be reentrant, the function may not use global and static data.

I do use global data "DNMTemp" in this case. However, DNMTemp's value is not changed and function only return its address.

c reentrancy

edited Jan 19 at 3:30

asked Jan 19 at 3:25

Andy Lin

517

edited Jan 19 at 3:30

asked Jan 19 at 3:25

Andy Lin

517

edited Jan 19 at 3:30

asked Jan 19 at 3:25

Andy Lin

517

asked Jan 19 at 3:25

Andy Lin

517

asked Jan 19 at 3:25

Andy Lin

517

3

This function is reentrant, but whatever you call it from probably isn't.

– Matt Timmermans
Jan 19 at 3:40

I don't understand it. Can you give me an example?

– Andy Lin
Jan 19 at 4:04

1

You are handing out the same pointer for every call, so everyone who calls it will be accessing the same object. Whatever function calls this one, it will probably use that pointer for something that could be messed up by a reentrant call to the same function.

– Matt Timmermans
Jan 19 at 4:17

What global data do you think it uses? It doesn't use the value of DNMTemp.

– David Schwartz
Jan 19 at 8:58

add a comment |

3

This function is reentrant, but whatever you call it from probably isn't.

– Matt Timmermans
Jan 19 at 3:40

I don't understand it. Can you give me an example?

– Andy Lin
Jan 19 at 4:04

1

You are handing out the same pointer for every call, so everyone who calls it will be accessing the same object. Whatever function calls this one, it will probably use that pointer for something that could be messed up by a reentrant call to the same function.

– Matt Timmermans
Jan 19 at 4:17

What global data do you think it uses? It doesn't use the value of DNMTemp.

– David Schwartz
Jan 19 at 8:58

This function is reentrant, but whatever you call it from probably isn't.

– Matt Timmermans
Jan 19 at 3:40

I don't understand it. Can you give me an example?

– Andy Lin
Jan 19 at 4:04

You are handing out the same pointer for every call, so everyone who calls it will be accessing the same object. Whatever function calls this one, it will probably use that pointer for something that could be messed up by a reentrant call to the same function.

– Matt Timmermans
Jan 19 at 4:17

What global data do you think it uses? It doesn't use the value of DNMTemp.

– David Schwartz
Jan 19 at 8:58

add a comment |

2 Answers
2

active

oldest

votes

Yes.

From the tag excerpt of reentrancy:

A subroutine is considered reentrant if it can be safely called before a previous call has completed.

In your case, since the function only returns the address of a global (static) variable, which should remain constant after the program starts, the function is well re-entrant.

IMO, reentrant function can access global and static data, without changing any, so obtaining the address of a global variable isn't bad for a reentrant function.

answered Jan 19 at 3:28

iBug

20.4k63864

To your IMO, if global/static data is being changed then what happens?

– Andy Lin
Jan 19 at 6:16

@AndyLin Consider this minimal example: f() { return ++x; } If it's called concurrently by two threads, the result may possibly be both threads getting x+2 as the result, when one of them would be expecting x+1.

– iBug
Jan 19 at 6:53

I meant, although reentrant function doesn't change data, but may reads data that is being changed(and still not complete) by other thread and result in wrong reading.

– Andy Lin
Jan 19 at 7:05

@AndyLin If the data is changed by something other than this function itself, it doesn't affect the reentrancy of this very function.

– iBug
Jan 19 at 7:10

add a comment |

When considering the if the function is reentrant or not the example has to be a bit less trivial than this one.

pDNM DNMManager_New(void)    //reentrant?

{

    return &DNMTemp;

}

But the reference to the DNMTemp (its address) will remain the same during the program execution so this function is reentrant.

But if you access any real data it will not.

uint32_t DNMManager_read(void)    //reentrant?

{

    return SerialNum;

}

answered Jan 19 at 8:50

P__J__

10.2k2723

add a comment |

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
});

}
});

draft saved

draft discarded

Sign up or log in

StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});

Post as a guest

Name

Required, but never shown

StackExchange.ready(
function () {
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fstackoverflow.com%2fquestions%2f54263819%2fis-this-function-re-entrant%23new-answer', 'question_page');
}
);

Post as a guest

Name

Required, but never shown

2 Answers
2

active

oldest

votes

2 Answers
2

active

oldest

votes

Yes.

From the tag excerpt of reentrancy:

A subroutine is considered reentrant if it can be safely called before a previous call has completed.

In your case, since the function only returns the address of a global (static) variable, which should remain constant after the program starts, the function is well re-entrant.

IMO, reentrant function can access global and static data, without changing any, so obtaining the address of a global variable isn't bad for a reentrant function.

answered Jan 19 at 3:28

iBug

20.4k63864

To your IMO, if global/static data is being changed then what happens?

– Andy Lin
Jan 19 at 6:16

@AndyLin Consider this minimal example: f() { return ++x; } If it's called concurrently by two threads, the result may possibly be both threads getting x+2 as the result, when one of them would be expecting x+1.

– iBug
Jan 19 at 6:53

I meant, although reentrant function doesn't change data, but may reads data that is being changed(and still not complete) by other thread and result in wrong reading.

– Andy Lin
Jan 19 at 7:05

@AndyLin If the data is changed by something other than this function itself, it doesn't affect the reentrancy of this very function.

– iBug
Jan 19 at 7:10

add a comment |

Yes.

From the tag excerpt of reentrancy:

A subroutine is considered reentrant if it can be safely called before a previous call has completed.

In your case, since the function only returns the address of a global (static) variable, which should remain constant after the program starts, the function is well re-entrant.

IMO, reentrant function can access global and static data, without changing any, so obtaining the address of a global variable isn't bad for a reentrant function.

answered Jan 19 at 3:28

iBug

20.4k63864

To your IMO, if global/static data is being changed then what happens?

– Andy Lin
Jan 19 at 6:16

@AndyLin Consider this minimal example: f() { return ++x; } If it's called concurrently by two threads, the result may possibly be both threads getting x+2 as the result, when one of them would be expecting x+1.

– iBug
Jan 19 at 6:53

I meant, although reentrant function doesn't change data, but may reads data that is being changed(and still not complete) by other thread and result in wrong reading.

– Andy Lin
Jan 19 at 7:05

@AndyLin If the data is changed by something other than this function itself, it doesn't affect the reentrancy of this very function.

– iBug
Jan 19 at 7:10

add a comment |

Yes.

From the tag excerpt of reentrancy:

A subroutine is considered reentrant if it can be safely called before a previous call has completed.

In your case, since the function only returns the address of a global (static) variable, which should remain constant after the program starts, the function is well re-entrant.

IMO, reentrant function can access global and static data, without changing any, so obtaining the address of a global variable isn't bad for a reentrant function.

answered Jan 19 at 3:28

iBug

20.4k63864

Yes.

From the tag excerpt of reentrancy:

A subroutine is considered reentrant if it can be safely called before a previous call has completed.

In your case, since the function only returns the address of a global (static) variable, which should remain constant after the program starts, the function is well re-entrant.

IMO, reentrant function can access global and static data, without changing any, so obtaining the address of a global variable isn't bad for a reentrant function.

answered Jan 19 at 3:28

iBug

20.4k63864

answered Jan 19 at 3:28

iBug

20.4k63864

answered Jan 19 at 3:28

iBug

20.4k63864

answered Jan 19 at 3:28

iBug

20.4k63864

To your IMO, if global/static data is being changed then what happens?

– Andy Lin
Jan 19 at 6:16

@AndyLin Consider this minimal example: f() { return ++x; } If it's called concurrently by two threads, the result may possibly be both threads getting x+2 as the result, when one of them would be expecting x+1.

– iBug
Jan 19 at 6:53

I meant, although reentrant function doesn't change data, but may reads data that is being changed(and still not complete) by other thread and result in wrong reading.

– Andy Lin
Jan 19 at 7:05

@AndyLin If the data is changed by something other than this function itself, it doesn't affect the reentrancy of this very function.

– iBug
Jan 19 at 7:10

add a comment |

To your IMO, if global/static data is being changed then what happens?

– Andy Lin
Jan 19 at 6:16

@AndyLin Consider this minimal example: f() { return ++x; } If it's called concurrently by two threads, the result may possibly be both threads getting x+2 as the result, when one of them would be expecting x+1.

– iBug
Jan 19 at 6:53

I meant, although reentrant function doesn't change data, but may reads data that is being changed(and still not complete) by other thread and result in wrong reading.

– Andy Lin
Jan 19 at 7:05

@AndyLin If the data is changed by something other than this function itself, it doesn't affect the reentrancy of this very function.

– iBug
Jan 19 at 7:10

To your IMO, if global/static data is being changed then what happens?

– Andy Lin
Jan 19 at 6:16

@AndyLin Consider this minimal example: f() { return ++x; } If it's called concurrently by two threads, the result may possibly be both threads getting x+2 as the result, when one of them would be expecting x+1.

– iBug
Jan 19 at 6:53

I meant, although reentrant function doesn't change data, but may reads data that is being changed(and still not complete) by other thread and result in wrong reading.

– Andy Lin
Jan 19 at 7:05

@AndyLin If the data is changed by something other than this function itself, it doesn't affect the reentrancy of this very function.

– iBug
Jan 19 at 7:10

add a comment |

When considering the if the function is reentrant or not the example has to be a bit less trivial than this one.

pDNM DNMManager_New(void)    //reentrant?

{

    return &DNMTemp;

}

But the reference to the DNMTemp (its address) will remain the same during the program execution so this function is reentrant.

But if you access any real data it will not.

uint32_t DNMManager_read(void)    //reentrant?

{

    return SerialNum;

}

answered Jan 19 at 8:50

P__J__

10.2k2723

add a comment |

When considering the if the function is reentrant or not the example has to be a bit less trivial than this one.

pDNM DNMManager_New(void)    //reentrant?

{

    return &DNMTemp;

}

But the reference to the DNMTemp (its address) will remain the same during the program execution so this function is reentrant.

But if you access any real data it will not.

uint32_t DNMManager_read(void)    //reentrant?

{

    return SerialNum;

}

answered Jan 19 at 8:50

P__J__

10.2k2723

add a comment |

When considering the if the function is reentrant or not the example has to be a bit less trivial than this one.

pDNM DNMManager_New(void)    //reentrant?

{

    return &DNMTemp;

}

But the reference to the DNMTemp (its address) will remain the same during the program execution so this function is reentrant.

But if you access any real data it will not.

uint32_t DNMManager_read(void)    //reentrant?

{

    return SerialNum;

}

answered Jan 19 at 8:50

P__J__

10.2k2723

When considering the if the function is reentrant or not the example has to be a bit less trivial than this one.

pDNM DNMManager_New(void)    //reentrant?

{

    return &DNMTemp;

}

But the reference to the DNMTemp (its address) will remain the same during the program execution so this function is reentrant.

But if you access any real data it will not.

uint32_t DNMManager_read(void)    //reentrant?

{

    return SerialNum;

}

answered Jan 19 at 8:50

P__J__

10.2k2723

answered Jan 19 at 8:50

P__J__

10.2k2723

answered Jan 19 at 8:50

P__J__

10.2k2723

answered Jan 19 at 8:50

P__J__

10.2k2723

add a comment |

draft saved

draft discarded

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.

draft saved

draft discarded

Sign up or log in

StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});

Post as a guest

Name

Required, but never shown

Post as a guest

Name

Required, but never shown

Sign up or log in

StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});

Post as a guest

Name

Required, but never shown

Sign up or log in

StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});

Post as a guest

Name

Required, but never shown

Sign up or log in

StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});

Post as a guest

Name

Required, but never shown

Name

Required, but never shown

Name

Required, but never shown

This page is only for reference, If you need detailed information, please check here

搜尋此網誌

Brtdku