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Add comments on String and Variant usage regarding memory contexts.

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Contributed by Cynthia Shang.
This commit is contained in:
Cynthia Shang 2018-12-06 11:53:38 -05:00 committed by David Steele
parent 11181e69b8
commit a72759eb5b
2 changed files with 28 additions and 0 deletions
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14
src/common/type/string.h
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@ -1,5 +1,19 @@
/***********************************************************************************************************************************
String Handler
Strings are lightweight objects in that they do not have their own memory context, instead they exist in the current context in
which they are instantiated. If a string is needed outside the current memory context, the memory context must be switched to the
old context and then back. Below is a simplified example:
String *result = NULL; <--- is created in the current memory context (referred to as "old context" below)
MEM_CONTEXT_TEMP_BEGIN() <--- begins a new temporary context
{
String *resultStr = strNewN("myNewStr"); <--- creates a string in the temporary memory context
memContextSwitch(MEM_CONTEXT_OLD()); <--- switch to the old context so the duplication of the string is in that context
result = strDup(resultStr); <--- recreates a copy of the string in the old context where "result" was created.
memContextSwitch(MEM_CONTEXT_TEMP()); <--- switch back to the temporary context
}
MEM_CONTEXT_TEMP_END(); <-- frees everything created inside this temporary memory context - i.e resultStr
***********************************************************************************************************************************/
#ifndef COMMON_TYPE_STRING_H
#define COMMON_TYPE_STRING_H

14
src/common/type/variant.h
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@ -1,5 +1,19 @@
/***********************************************************************************************************************************
Variant Data Type
Variants are lightweight objects in that they do not have their own memory context, instead they exist in the current context in
which they are instantiated. If a variant is needed outside the current memory context, the memory context must be switched to the
old context and then back. Below is a simplified example:
Variant *result = NULL; <--- is created in the current memory context (referred to as "old context" below)
MEM_CONTEXT_TEMP_BEGIN() <--- begins a new temporary context
{
String *resultStr = strNewN("myNewStr"); <--- creates a string in the temporary memory context
memContextSwitch(MEM_CONTEXT_OLD()); <--- switch to old context so creation of the variant from the string is in old context
result = varNewUInt64(cvtZToUInt64(strPtr(resultStr))); <--- recreates variant from the string in the old context.
memContextSwitch(MEM_CONTEXT_TEMP()); <--- switch back to the temporary context
}
MEM_CONTEXT_TEMP_END(); <-- frees everything created inside this temporary memory context - i.e resultStr
***********************************************************************************************************************************/
#ifndef COMMON_TYPE_VARIANT_H
#define COMMON_TYPE_VARIANT_H