hashmap

Hashmap implementation written in C

Hashmaps are a key value store with quick look up times. The hashmap_stats() function will provide a summary of the current lookup times including average, worst case key not found, and worst case key found.

This hashmap implementation is a simple and, generally, quick method to include a hashmap in C programs. It was developed to provide a basis for testing and benchmarking performance along with providing a purposeful, low overhead library.

To use the library, copy the src/hashmap.h and src/hashmap.c files into your project, compile and link the library, and include it where needed.

NOTE: The key is of type char* as in a c-string

License

MIT 2016

Usage:

#include "hashmap.h"

HashMap h;
hashmap_init(&h);

hashmap_set_string(&h, "google", "search engine, android, web ads");
hashmap_set_string(&h, "facebook", "social media site");
hashmap_set_string(&h, "twitter", "the sound of little birds");

char* tmp = (char*)hashmap_get(&h, "google");
if (tmp == NULL) {
    printf("'google' was not in the hashmap\n");
} else {
    printf("key: test\tvalue: %s\n", tmp);
    hashmap_set_string(&h, "google", "search engine, android, web ads, and automobiles");
}

hashmap_stats(&h);
hashmap_destroy(&h);

Thread safety

Due to the the overhead of enforcing thread safety, it is up to the user to ensure that each thread has controlled access to the hashmap. For OpenMP code, the following should suffice.

#include "set.h"
#include <omp.h>

int main(int argc, char** argv) {
    HashMap h;
    hashmap_init(&h);

    #pragma omp parallel for
    for (int i = 0; i < 500000; i++) {
        char key[KEY_LEN] = {0};
        sprintf(key, "%d", i);

        #pragma omp critical (hashmap_set_lock)
        {
            hashmap_add_int(&h, key, i);
        }
    }
    hashmap_destroy(&h);
}

Guards must be used when inserting and removing elements as the layout of the nodes may change. When there are only retrievals, hashmap_get, then there is no need for guards. If the retrievals are simultaneous to the insertions and deletions then guards must be placed around hashmap_get to ensure that the node location doesn't change.

Required Compile Flags:

None

Future Enhancements: