8000 [BUG] kernel/msgqueue.h -- Not Bug. · Issue #353 · sogou/workflow · GitHub
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[BUG] kernel/msgqueue.h -- Not Bug. #353

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daidai21 opened this issue May 2, 2021 · 4 comments
Closed

[BUG] kernel/msgqueue.h -- Not Bug. #353

daidai21 opened this issue May 2, 2021 · 4 comments

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@daidai21
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daidai21 commented May 2, 2021 
#include <stdio.h>
#include "./msgqueue.h"

int main(int argc, char* argv[]) {
  msgqueue_t* tmp_mq = msgqueue_create(10, 0);
  char str[] = "hello";

  msgqueue_put(str, tmp_mq);
  char* p = msgqueue_get(tmp_mq);
  printf("%s\n", p);
  printf("%c\n", *p++);

  return 0;
}
➜  workflow gcc example.c msgqueue.c;./a.out
[1]    64749 segmentation fault  ./a.out
@Barenboim
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Barenboim commented May 2, 2021 •
edited
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Not a bug.
The second argument of msgqueue_create() is the offset from the head each message, where users have to reserve bytes of a pointer size for internal linking. This will reduce the allocating and freeing of memory.
In you case, maybe:

int main(void)
{
    msgqueue_t *mq = msgqueue_create(10, -sizeof (void *));
    char str[sizeof (void *) + 6];
    char *p = str + sizeof (void *);
    strcpy(p, "hello");
    msgqueue_put(p, mq);
    p = msgqueue_get(mq);
    printf("%s\n", p);
    return 0;
}

@Barenboim Barenboim changed the title [BUG] kernel/msgqueue.h [BUG] kernel/msgqueue.h -- Not Bug. May 2, 2021
@daidai21 daidai21 closed this as completed May 3, 2021
@sourcema
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Not a bug. The second argument of msgqueue_create() is the offset from the head each message, where users have to reserve bytes of a pointer size for internal linking. This will reduce the allocating and freeing of memory. In you case, maybe:

int main(void)
{
    msgqueue_t *mq = msgqueue_create(10, -sizeof (void *));
    char str[sizeof (void *) + 6];
    char *p = str + sizeof (void *);
    strcpy(p, "hello");
    msgqueue_put(p, mq);
    p = msgqueue_get(mq);
    printf("%s\n", p);
    return 0;
}

请问下我改成这样为什么输出为空了：
msgqueue_t *mq = msgqueue_create(10, -1);
char str[1 + 6];
char p = str + 1;
strcpy(p, "hello");
msgqueue_put(p, mq);
p = (char)msgqueue_get(mq);
printf("%s\n", p);
return 0;

@Barenboim
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Linkoff的位置，需要用户预留一个指针大小的空间。内部要拉链的。

@sourcema
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Linkoff的位置，需要用户预留一个指针大小的空间。内部要拉链的。

好的，谢谢

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@daidai21 @sourcema @Barenboim
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