hydra: using HASH_REPLACE_STR instead of HASH_ADD_STR

[Jayyee-HPC]

Pull Request Description

Currently PMI server adds KVSs to the hash table without checking if same key exsiting, which may cause undefined behaviors since same keys are not allowed in Uthash.

A stable way to reproduce related bugs.

    char kvsname[KVSNAMELEN];
    char kvs_key[MAXKEYLEN];
    char value[MAXVALLEN];
    char get_value[MAXVALLEN];
    uint64_t key = 1001;
    uint64_t val = key;

    PMI_KVS_Get_my_name(kvsname, KVSNAMELEN);
    for (int i = 0; i < 101; ++i)
    {
        val++;
        char kvs_key[MAXKEYLEN];
        sprintf(kvs_key, "%.16"PRIx64"", key);
        sprintf(value, "%.16"PRIx64"", val);
        PMI_KVS_Put(kvsname, kvs_key, value);
        PMI_Barrier();
        PMI_KVS_Get(kvsname, kvs_key, get_value, MAXVALLEN);
        printf("P%d itr %d put %s get %s\n", comm_ptr->rank, i, value, get_value);
    }

Two issues can be found:
1.Using this test case, the same key with different values can be pushed without any warning.
2.In cases using 2 processes, the 10th and 100th iteration, the values are lost.

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[hzhou]

Whitespace checker is for each commit. You need to squash the commits in order to pass.

[Jayyee-HPC]

Whitespace checker is for each commit. You need to squash the commits in order to pass.

Thanks. The Whitespace checker is so frustrating.

[raffenet]

What is the use-case for replacing values in the KVS? FYI, this type of behavior is not allowed by PMI1 and PMI2, though as you found, Hydra does not explicitly check for duplicate keys. It would be good to understand what you are trying to enable.

[hzhou]

What is the use-case for replacing values in the KVS? FYI, this type of behavior is not allowed by PMI1 and PMI2, though as you found, Hydra does not explicitly check for duplicate keys. It would be good to understand what you are trying to enable.

It's for heartbeat implementation. The heartbeat needs to update its status.

[hzhou]

Picked in PR #6564