Segmentation fault while setting hiredis.hiredisAllocFuncs by je_malloc

Debugging a Segmentation Fault with Jemalloc and Hiredis in a C Project

Recently, I encountered a perplexing issue while integrating jemalloc into a C project that also makes use of the Hiredis library. I want to share my experience and the solution I found, which might help others facing similar challenges.

The Setup

My goal was to enhance memory management in a project that utilizes Hiredis for Redis interactions. To achieve this, I opted to use jemalloc, a memory allocation library known for its performance benefits. I compiled jemalloc v5.3.0 with the configure command argument --with-jemalloc-prefix=jee_ to avoid namespace collisions. This prefix is intended to redefine jemalloc’s malloc, calloc, etc., to jee_malloc, jee_calloc, and so on.

In the C code, I updated Hiredis allocation functions to use these custom-prefixed functions from jemalloc:

hiredisAllocFuncs myfuncs = {
    .mallocFn = jee_malloc,
    .callocFn = jee_calloc,
    .reallocFn = jee_realloc,
    .strdupFn = strdup,  // Note: strdup is not prefixed
    .freeFn = jee_free,
};

hiredisAllocFuncs orig = hiredisSetAllocators(&myfuncs);

With these changes, I compiled the project using the GCC with options linking to Hiredis, pthread, and jemalloc. However, running the compiled binary resulted in a segmentation fault.

The Issue

Using GDB, I traced the problem to the function tcache_bin_flush_impl inside jemalloc, which deals with thread-specific cache bins of memory. This indicated that the issue was likely related to how memory allocation and deallocation were being handled across different threads.

The Investigation

Upon closer inspection and repeated trials, I discovered that using the built-in allocation functions without the prefix (i.e., replacing jee_malloc with malloc and so forth directly in the Hiredis allocator setup), the segmentation fault vanished, and the application functioned as expected.

This clue suggested that there could be an inconsistency or hidden bug linked with the prefixed versions of the memory management functions—perhaps an initialization issue or a mismatch in how the memory was being managed across different parts of the application.

The Solution

After much reflection and debugging, I chose to simplify the configuration by removing the custom prefix:

1. I recompiled jemalloc without the --with-jemalloc-prefix argument.

1. Aligned the allocation function pointers directly to the default names (malloc, free, etc.).

This adjustment, although it dismissed the use of the custom prefix (intended to avoid symbol conflicts), resolved the segmentation fault entirely.

Conclusion

This journey taught me that while custom prefixes for libraries like jemalloc can be useful for avoiding namespace issues, they can introduce complications—especially if not every system component (like thread-specific data in jemalloc) handles them gracefully. This experience emphasized the importance of thorough testing when integrating multiple complex libraries, particularly in multithreaded environments.

Analyzing the subtle ways in which different libraries interact and ensuring compatibility across different system layers is essential, especially in managing memory in multi-threaded applications. Sometimes, a simpler configuration not only works better but also avoids unexpected issues down the road. If you ever find yourself in a similar situation, consider taking a step back and reevaluating the complexity of your solution. Simplification might just be the key.