dev:shared_strings
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dev:shared_strings [2007/03/22 08:19] 127.0.0.1 external edit |
dev:shared_strings [2018/04/13 05:23] (current) karl Add headline, formatting, add sstring, remove FIXME, add FIXME SVN viewvc |
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| - | To minimize memory use, Crossfire uses a shared string mechanism. This is intended to be used for strings whose contents is not expected to change during the server's life. Using shared strings saves memory and improved performance. | + | ====== Shared String ====== |
| - | Those strings are used like regular ''const char*'', but should not be changed via ''strcpy'', ''snprintf'' or other means because it would affect **all** structures using the shared string. Internally, they use a counter to track at how many places they are used. When it reaches 0, string is freed. | + | To minimize memory use, Crossfire uses a shared string mechanism. \\ |
| + | This is intended to be used for strings whose contents are not expected to change during the server's life. \\ | ||
| + | Using shared strings saves memory and improved performance. | ||
| + | Those strings are used like regular ''const char*'', \\ | ||
| + | but should not be changed via ''strcpy'', ''snprintf'' or other means \\ | ||
| + | because it would affect **all** structures using the shared string. \\ | ||
| + | Internally, they use a counter to track at how many places they are used. \\ | ||
| + | When it reaches 0, string is freed. | ||
| + | |||
| + | ---- | ||
| + | |||
| + | ===== Shared String Manipulation == | ||
| To alter such a string, the right behaviour is: | To alter such a string, the right behaviour is: | ||
| * write new value in a ''char[] new_value'' variable | * write new value in a ''char[] new_value'' variable | ||
| Line 8: | Line 19: | ||
| * call ''str = add_string(new_value)'' | * call ''str = add_string(new_value)'' | ||
| - | FIXME replace with sstring when done in code | + | To manipulate them, the following functions defined in \\ |
| + | [[http://crossfire.svn.sourceforge.net/viewvc/crossfire/server/trunk/common/shstr.c?view=markup|common/shstr.c]] <- FIXME file location \\ | ||
| + | are available: | ||
| + | * Old: ''const char* add_string(const char *str)'' | ||
| + | * New: ** ''sstring add_string(const char *str)'' ** | ||
| + | * Used to share an existing string. | ||
| + | * Returned value is a string with the same contents of ''str'' that can be shared with other objects. | ||
| + | * Returns return hash_table[ind]->string | ||
| + | |||
| + | * Old: ''const char* add_refcount(const char *str)'' | ||
| + | * New: ** ''sstring add_refcount(sstring str)'' ** | ||
| + | * This will increase the refcount of the string str. | ||
| + | * String str which *must* have been returned from a previous add_string(). | ||
| + | * :?: Equivalent of ''add_string'' when the string is already a shared string. :?: | ||
| + | |||
| + | |||
| + | * Old: ''const char* find_string(const char *str)'' | ||
| + | * New: ** ''sstring find_string(const char *str)'' ** | ||
| + | * To search if a string is shared or not. | ||
| + | * Returns pointer to identical string or NULL . | ||
| + | |||
| + | |||
| + | * Old: ''void free_string(const char *str)'' | ||
| + | * New: ** ''void free_string(sstring str)'' ** | ||
| + | * To decrement the use refcount counter. | ||
| + | * *Must* have been returned from a previous add_string(). | ||
| + | * After it's called, ''str'' should not be used anymore. | ||
| + | |||
| + | Because shared strings will return a pointer to a string if it exists, \\ | ||
| + | one can see if the strings are equal by comparing the shared string address they point to (ie ''str == str2'') directly. | ||
| + | |||
| + | ---- | ||
| + | |||
| + | ===== SSTRING ===== | ||
| + | sstring is defined in //server/include/shstr.h// since at least version 1.11.0 : | ||
| + | <code c> | ||
| + | /** | ||
| + | * One actual shared string. | ||
| + | */ | ||
| + | typedef struct _shared_string { | ||
| + | union { | ||
| + | struct _shared_string **array; | ||
| + | struct _shared_string *previous; | ||
| + | } u; | ||
| + | struct _shared_string *next; | ||
| + | /* The top bit of "refcount" is used to signify that "u.array" points | ||
| + | * at the array entry. | ||
| + | */ | ||
| + | unsigned REFCOUNT_TYPE refcount; | ||
| + | /* Padding will be unused memory, since we can't know how large | ||
| + | * the padding when allocating memory. We assume here that | ||
| + | * sizeof(long) is a good boundary. | ||
| + | */ | ||
| + | char string[PADDING]; | ||
| + | } shared_string; | ||
| + | </code> | ||
| + | |||
| + | ---- | ||
| - | To manipulate them, the following functions (defined in ''[[http://crossfire.svn.sourceforge.net/viewvc/crossfire/server/trunk/common/shstr.c?view=markup|common/shstr.c]]'') are available: | + | ===== Trivial == |
| - | * ''const char* add_string(const char *str)'', used to share a string. Returned value is a string with the same contents that can be shared with other objects | + | <code c> |
| - | * ''const char* add_refcount(const char *str)'', equivalent of ''add_string'' when the string is already a shared string | + | /** |
| - | * ''const char* find_string(const char *str)'', to search if a string is shared or not | + | * @file shstr.c |
| - | * ''void free_string(const char *str)'', to decrement the use counter. After it's called, ''str'' should not be used anymore. | + | * This is a simple shared strings package with a simple interface. |
| + | * | ||
| + | * Author: Kjetil T. Homme, Oslo 1992. | ||
| + | */ | ||
| + | </code> | ||
| - | Because shared strings will return a pointer to a string if it exists, one can see if the strings are equal by comparing the shared string address they point to (ie ''str == str2'' directly). | ||
dev/shared_strings.1174569577.txt.gz · Last modified: 2018/04/13 05:23 (external edit)
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