From 9c76875f413190a547244e72a3f9e9bbeb6811e9 Mon Sep 17 00:00:00 2001
From: Yossi Gottlieb <yossigo@gmail.com>
Date: Fri, 23 Jun 2017 10:29:49 +0300
Subject: [PATCH] Add RM_ModuleTypeReplaceValue.

This is a light-weight replace function, useful for use cases such as
realloc()ing an existing value, etc.  Using RM_ModuleTypeSetValue() in
such cases is wasteful and complex as it attempts to delete the old
value, call its destructor, etc.
---
 src/module.c      | 29 ++++++++++++++++++++++++++++-
 src/redismodule.h |  2 ++
 2 files changed, 30 insertions(+), 1 deletion(-)

diff --git a/src/module.c b/src/module.c
index ad34e7b64..0f22178c9 100644
--- a/src/module.c
+++ b/src/module.c
@@ -1950,7 +1950,7 @@ int RM_DeleteKey(RedisModuleKey *key) {
     return REDISMODULE_OK;
 }
 
-/* If the key is open for writing, unlink it (that is delete it in a 
+/* 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
@@ -6768,6 +6768,32 @@ int RM_GetLRUOrLFU(RedisModuleKey *key, long long *lfu_freq, long long *lru_idle
     return REDISMODULE_OK;
 }
 
+/* Replace the value assigned to a module type.
+ *
+ * The key must be open for writing, have an existing value, and have a moduleType
+ * that matches the one specified by the caller.
+ *
+ * Unlike RM_ModuleTypeSetValue() which will free the old value, this function
+ * simply swaps the old value with the new value.
+ *
+ * The function returns the old value, or NULL if any of the above conditions is
+ * not met.
+ */
+void *RM_ModuleTypeReplaceValue(RedisModuleKey *key, moduleType *mt, void *new_value) {
+    if (!(key->mode & REDISMODULE_WRITE) || key->iter)
+        return NULL;
+    if (!key->value || key->value->type != OBJ_MODULE)
+        return NULL;
+
+    moduleValue *mv = key->value->ptr;
+    if (mv->type != mt)
+        return NULL;
+
+    void *old_val = mv->value;
+    mv->value = new_value;
+    return old_val;
+}
+
 /* Register all the APIs we export. Keep this function at the end of the
  * file so that's easy to seek it to add new entries. */
 void moduleRegisterCoreAPI(void) {
@@ -6857,6 +6883,7 @@ void moduleRegisterCoreAPI(void) {
     REGISTER_API(PoolAlloc);
     REGISTER_API(CreateDataType);
     REGISTER_API(ModuleTypeSetValue);
+    REGISTER_API(ModuleTypeReplaceValue);
     REGISTER_API(ModuleTypeGetType);
     REGISTER_API(ModuleTypeGetValue);
     REGISTER_API(IsIOError);
diff --git a/src/redismodule.h b/src/redismodule.h
index 728c7f584..8cf789fb0 100644
--- a/src/redismodule.h
+++ b/src/redismodule.h
@@ -517,6 +517,7 @@ int REDISMODULE_API_FUNC(RedisModule_GetContextFlags)(RedisModuleCtx *ctx);
 void *REDISMODULE_API_FUNC(RedisModule_PoolAlloc)(RedisModuleCtx *ctx, size_t bytes);
 RedisModuleType *REDISMODULE_API_FUNC(RedisModule_CreateDataType)(RedisModuleCtx *ctx, const char *name, int encver, RedisModuleTypeMethods *typemethods);
 int REDISMODULE_API_FUNC(RedisModule_ModuleTypeSetValue)(RedisModuleKey *key, RedisModuleType *mt, void *value);
+void *REDISMODULE_API_FUNC(RedisModule_ModuleTypeReplaceValue)(RedisModuleKey *key, RedisModuleType *mt, void *new_value);
 RedisModuleType *REDISMODULE_API_FUNC(RedisModule_ModuleTypeGetType)(RedisModuleKey *key);
 void *REDISMODULE_API_FUNC(RedisModule_ModuleTypeGetValue)(RedisModuleKey *key);
 int REDISMODULE_API_FUNC(RedisModule_IsIOError)(RedisModuleIO *io);
@@ -726,6 +727,7 @@ static int RedisModule_Init(RedisModuleCtx *ctx, const char *name, int ver, int
     REDISMODULE_GET_API(PoolAlloc);
     REDISMODULE_GET_API(CreateDataType);
     REDISMODULE_GET_API(ModuleTypeSetValue);
+    REDISMODULE_GET_API(ModuleTypeReplaceValue);
     REDISMODULE_GET_API(ModuleTypeGetType);
     REDISMODULE_GET_API(ModuleTypeGetValue);
     REDISMODULE_GET_API(IsIOError);
-- 
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