Question

Are g_hash_table_lookup and g_hash_table_insert thread-safe? Can I use code like this:

dict = g_hash_table_new();
for (i = 0; i < N; i++) {
    compute_A();
    find_hash_of_A();
    void *value = g_hash_table_lookup(dict, key);
    struct MyStruct *obj;
    if (!value) {
        obj = (struct MyStruct *)value;
    } else {
        compute_obj
        g_hash_table_insert(dict, key, obj);
    }
    do_something_with_obj
}

with #pragma omp parallel for, or I need to use some other OpenMP pragmas?
At times I got an error in that loop. One thread version works fine.

Answer 1

No. From the Threads section of the GLib Reference Manual:

GLib itself is internally completely thread-safe (all global data is automatically locked), but individual data structure instances are not automatically locked for performance reasons. For example, you must coordinate accesses to the same GHashTable from multiple threads. The two notable exceptions from this rule are GMainLoop and GAsyncQueue, which are thread-safe and need no further application-level locking to be accessed from multiple threads. Most refcounting functions such as g_object_ref() are also thread-safe.