Redis Modules: Ctx becomes inaccessible upon exiting Callback Function

[Dhruv Umesh]

Hello all,

I am currently writing a module that will first set 10 keys in the database, and then iterate through the keys using RedisModule_Scan, printing the key value pairs where the value is greater than 10. However, during testing, I keep getting a segmentation fault in line 3672 in moduleInitKey(): kp->db = ctx->client->db; . Using gdb, I've determined that this happens because the ctx object becomes inaccessible after exiting the callback function. I have attached my code below. Any help/advice on this matter is appreciated.

Thanks in advance,

Dhruv.

#include "../../redis/src/redismodule.h"

#include <stdlib.h>

void redisModuleScanCallback(RedisModuleCtx *ctx, RedisModuleString *keyname,

                   RedisModuleKey *key, void *privdata) {

        size_t len = 0;

        //double *threshold = (double *) privdata;

        RedisModule_Log(ctx, REDISMODULE_LOGLEVEL_NOTICE, "Pre key read");

        const char *val = RedisModule_StringDMA(key, &len, REDISMODULE_READ);

        //RedisModule_Log(ctx, REDISMODULE_LOGLEVEL_NOTICE, "Val: %s", val);

        double *d;

        sscanf(val, "%lf", d);

        if(*d >= 10.0){ //I'm not using the threshold variable for now

                RedisModule_Log(ctx, REDISMODULE_LOGLEVEL_NOTICE, "Hit -> %s", val);

        } else {

                RedisModule_Log(ctx, REDISMODULE_LOGLEVEL_NOTICE, "Miss");

        }

        return;

}

void populateDB(RedisModuleCtx *ctx){

        for(int i = 0; i < 10; i++){

                const char k = 65 + i;

                size_t len;

                int v = i+5;

                RedisModuleString *val = RedisModule_CreateStringPrintf(ctx, "%d", v);

                RedisModuleString *keyname = RedisModule_CreateStringPrintf(ctx, "%c", k);

                RedisModuleKey *key = RedisModule_OpenKey(ctx, keyname, REDISMODULE_WRITE);

                int status = RedisModule_StringSet(key, val);

                if (status == REDISMODULE_ERR)

                        RedisModule_Log(ctx, REDISMODULE_LOGLEVEL_NOTICE, "Error setting");

        }

        return;

}

int getKeyValuePairs(RedisModuleCtx *ctx, RedisModuleString **argv, int argc) {

        if(argc != 2)

                return RedisModule_WrongArity(ctx);

        RedisModule_AutoMemory(ctx);

        populateDB(ctx);

        double threshold = 0;

        if(RedisModule_StringToDouble(argv[1], &threshold) == REDISMODULE_ERR)

                return REDISMODULE_ERR;

        int num_keys = (int) RedisModule_DbSize(ctx), key_count = 0;

        RedisModule_Log(ctx, REDISMODULE_LOGLEVEL_NOTICE, "Num keys: %d", num_keys);

        RedisModuleScanCursor *cursor = RedisModule_ScanCursorCreate();

        while(RedisModule_Scan(ctx, cursor, redisModuleScanCallback, NULL));

        RedisModule_ScanCursorDestroy(cursor);

        return REDISMODULE_OK;

}

int RedisModule_OnLoad(RedisModuleCtx *ctx) {

        if (RedisModule_Init(ctx, "keyQueries", 1, REDISMODULE_APIVER_1) == REDISMODULE_ERR) {

                return REDISMODULE_ERR;

        }

        if (RedisModule_CreateCommand(ctx, "GETVALUESGEQ", getKeyValuePairs,

                "write", 1,1,1) == REDISMODULE_ERR) {

                return REDISMODULE_ERR;

        }

}

[Dhruv Umesh]

Update: I've solved my problem. I'm not sure why but sscanf was the issue.