Added RM_UnlinkKey - a low level analog to UNLINK command

src/module.c

@@ -1456,6 +1456,20 @@ int RM_DeleteKey(RedisModuleKey *key) {
     return REDISMODULE_OK;
 }
 
+/* If the key is open for writing, unlink it (that is delete it in a 
+ * non-blocking way, not reclaiming memory immediately) and setup the key to
+ * accept new writes as an empty key (that will be created on demand).
+ * On success REDISMODULE_OK is returned. If the key is not open for
+ * writing REDISMODULE_ERR is returned. */
+int RM_UnlinkKey(RedisModuleKey *key) {
+    if (!(key->mode & REDISMODULE_WRITE)) return REDISMODULE_ERR;
+    if (key->value) {
+        dbAsyncDelete(key->db,key->key);
+        key->value = NULL;
+    }
+    return REDISMODULE_OK;
+}
+
 /* Return the key expire value, as milliseconds of remaining TTL.
  * If no TTL is associated with the key or if the key is empty,
  * REDISMODULE_NO_EXPIRE is returned. */
@@ -3960,6 +3974,7 @@ void moduleRegisterCoreAPI(void) {
     REGISTER_API(Replicate);
     REGISTER_API(ReplicateVerbatim);
     REGISTER_API(DeleteKey);
+    REGISTER_API(UnlinkKey);
     REGISTER_API(StringSet);
     REGISTER_API(StringDMA);
     REGISTER_API(StringTruncate);

src/modules/testmodule.c

@@ -120,6 +120,38 @@ int TestStringPrintf(RedisModuleCtx *ctx, RedisModuleString **argv, int argc) {
     return REDISMODULE_OK;
 }
 
+int failTest(RedisModuleCtx *ctx, const char *msg) {
+    RedisModule_ReplyWithError(ctx, msg);
+    return REDISMODULE_ERR;
+}
+int TestUnlink(RedisModuleCtx *ctx, RedisModuleString **argv, int argc) {
+    RedisModule_AutoMemory(ctx);
+    REDISMODULE_NOT_USED(argv);
+    REDISMODULE_NOT_USED(argc);
+
+    RedisModuleKey *k = RedisModule_OpenKey(ctx, RedisModule_CreateStringPrintf(ctx, "unlinked"), REDISMODULE_WRITE | REDISMODULE_READ);
+    if (!k) return failTest(ctx, "Could not create key");
+    
+    if (REDISMODULE_ERR == RedisModule_StringSet(k, RedisModule_CreateStringPrintf(ctx, "Foobar"))) {
+        return failTest(ctx, "Could not set string value");
+    }
+
+    RedisModuleCallReply *rep = RedisModule_Call(ctx, "EXISTS", "c", "unlinked");
+    if (!rep || RedisModule_CallReplyInteger(rep) != 1) {
+        return failTest(ctx, "Key does not exist before unlink");
+    }
+
+    if (REDISMODULE_ERR == RedisModule_UnlinkKey(k)) {
+        return failTest(ctx, "Could not unlink key");
+    }
+
+    rep = RedisModule_Call(ctx, "EXISTS", "c", "unlinked");
+    if (!rep || RedisModule_CallReplyInteger(rep) != 0) {
+        return failTest(ctx, "Could not verify key to be unlinked");
+    }
+    return RedisModule_ReplyWithSimpleString(ctx, "OK");
+    
+}
 
 /* TEST.CTXFLAGS -- Test GetContextFlags. */
 int TestCtxFlags(RedisModuleCtx *ctx, RedisModuleString **argv, int argc) {
@@ -269,6 +301,9 @@ int TestIt(RedisModuleCtx *ctx, RedisModuleString **argv, int argc) {
     T("test.string.append","");
     if (!TestAssertStringReply(ctx,reply,"foobar",6)) goto fail;
 
+    T("test.unlink","");
+    if (!TestAssertStringReply(ctx,reply,"OK",2)) goto fail;
+
     T("test.string.append.am","");
     if (!TestAssertStringReply(ctx,reply,"foobar",6)) goto fail;
 
@@ -311,6 +346,10 @@ int RedisModule_OnLoad(RedisModuleCtx *ctx, RedisModuleString **argv, int argc)
         TestCtxFlags,"readonly",1,1,1) == REDISMODULE_ERR)
         return REDISMODULE_ERR;
     
+    if (RedisModule_CreateCommand(ctx,"test.unlink",
+        TestUnlink,"write deny-oom",1,1,1) == REDISMODULE_ERR)
+        return REDISMODULE_ERR;
+
     if (RedisModule_CreateCommand(ctx,"test.it",
         TestIt,"readonly",1,1,1) == REDISMODULE_ERR)
         return REDISMODULE_ERR;

src/redismodule.h

@@ -185,6 +185,7 @@ int REDISMODULE_API_FUNC(RedisModule_ReplicateVerbatim)(RedisModuleCtx *ctx);
 const char *REDISMODULE_API_FUNC(RedisModule_CallReplyStringPtr)(RedisModuleCallReply *reply, size_t *len);
 RedisModuleString *REDISMODULE_API_FUNC(RedisModule_CreateStringFromCallReply)(RedisModuleCallReply *reply);
 int REDISMODULE_API_FUNC(RedisModule_DeleteKey)(RedisModuleKey *key);
+int REDISMODULE_API_FUNC(RedisModule_UnlinkKey)(RedisModuleKey *key);
 int REDISMODULE_API_FUNC(RedisModule_StringSet)(RedisModuleKey *key, RedisModuleString *str);
 char *REDISMODULE_API_FUNC(RedisModule_StringDMA)(RedisModuleKey *key, size_t *len, int mode);
 int REDISMODULE_API_FUNC(RedisModule_StringTruncate)(RedisModuleKey *key, size_t newlen);
@@ -306,6 +307,7 @@ static int RedisModule_Init(RedisModuleCtx *ctx, const char *name, int ver, int
     REDISMODULE_GET_API(Replicate);
     REDISMODULE_GET_API(ReplicateVerbatim);
     REDISMODULE_GET_API(DeleteKey);
+    REDISMODULE_GET_API(UnlinkKey);
     REDISMODULE_GET_API(StringSet);
     REDISMODULE_GET_API(StringDMA);
     REDISMODULE_GET_API(StringTruncate);