CODEWITHSUNDEEP
cfile-descriptor
skanzariya
skanzariya

Reputation: 407

C program, strange behaviour

Recently I came across the problem of geting 'Oops, Spwan error, can not allocate memory' while working with one C Application.

To understand the File Descriptor and Memory management better I give a try this sample program and it gives me shocking result.

Here is the code.

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

int main(int ac, char *av[]);

int main(int ac, char *av[])
{
int fd = 0;
unsigned long counter=0;
while (1)
{
char *aa = malloc(16384);
usleep(5);
fprintf(stderr,"Counter is %ld \n", counter);
fd = fopen("/dev/null",r")
}

return 0;
}

Here in the sample program I am trying to allocate memory every 5 micro second and also open a file descriptor at the same time.

Now when I run the program it started increasing the memory and also file descriptor star increasing, but memory increase upto 82.5% and file descriptor increase upto 1024. I know 'ulimit' set this parameter and it is 1024 by default.

But this program must crash by eating the memory or it should gives error ' Can't spawn child', but it is working.

So Just wanted to know why it is not crashing and why it is not giving child error as it reached file descriptor limit.

Upvotes: 0

Views: 200

Answers (2)

Maresh
Maresh

Reputation: 4712

What's the point in doing that?

Plus on linux, the system won't even eat up the memory if nothing is actually written on "aa".

And anyway, if you could actually take all the memory (which will never happen, for Linux and *bsd, don't know about windows), it would just result in making the system lag like hell or even freeze, not just crashing your application.

Upvotes: 0

user529758
user529758

Reputation:

It's not crashing probably because when malloc() finds no more memory to allocate and return, it simply returns NULL. Likewise, open() also just returns a negative value. In other words, the cooperation of your OS and the standard library is smarter than it would enable your program to crash.

Upvotes: 2

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