memory leak in dlopen / dlcose, or user error?

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Calling dlopen then dlclose causes an increase in the amount of memory used by the program. If I create a loop that calls dlopen / dlclose repeatedly on the same dynamic library, memory usage increases continuously. Is this a bug, or am I using dlopen / dlclose incorrectly?

I can reproduce this by modifying the sample code in the Apple Developer docs Creating Dynamic Libraries. If I modify Runtime.c, changing the line void *lib_handle = dlopen(lib_name, RTLD_NOW); to add the infinite loop, as below:

void *lib_handle = dlopen(lib_name, RTLD_NOW);
for (int ii = 0; ; ++ii) {
    printf("loop %i\n", ii);
    int close_err = dlclose(lib_handle);
    printf("close error: %i\n", close_err);
    printf("dlopen(%s, RTLD_NOW)\n", lib_name);
    lib_handle = dlopen(lib_name, RTLD_NOW);
}

then opening and closing the dynamic library will succeed, but memory usage (as reported by top) will rapidly increase.

I'm running on x86_64 macOS 13.6.6. Full code for the modified Runtime.c is attached, the rest of the code is available in the Apple Developer docs.

Any suggestions?

Many thanks, Chris

Runtime.c

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Answer 1

DTS Engineer OP

Apple

8h

I'm running on x86_64 macOS 13.6.6

Are you able to reproduce this on a more modern version of macOS?

There’s a couple of reasons why this matters:

The dynamic linker has received significant updates in the last few years, so it’s possible that this is fixed already.
If that’s the case, there’s no point filing a bug against macOS 13 because there’s no release vehicle for such a fix.

Notwithstanding the above, be aware that dlclose has a significant limitation on macOS: In many cases its unable to actually unload the library. This limitation is fundamental to the system, rather than a bug. The dlclose man page lists some of the causes, but those are just the start.

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