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Eina_Stringshare_Group

NAME

Stringshare -

These functions allow you to store one copy of a string, and use it throughout your program.

Functions

static Eina_Bool eina_stringshare_replace (const char **p_str, const char *news)
Replace the previously stringshared pointer with a new content.
EAPI const char * eina_stringshare_add_length (const char *str, unsigned int slen)
Retrieve an instance of a string for use in a program.
EAPI const char * eina_stringshare_add (const char *str)
Retrieve an instance of a string for use in a program.
EAPI const char * eina_stringshare_ref (const char *str)
Increment references of the given shared string.
EAPI void eina_stringshare_del (const char *str)
Note that the given string has lost an instance.
EAPI int eina_stringshare_strlen (const char *str)
Note that the given string must be shared.
EAPI void eina_stringshare_dump (void)
Dump the contents of the stringshare.

Detailed Description

These functions allow you to store one copy of a string, and use it throughout your program.

This is a method to reduce the number of duplicated strings kept in memory. It's pretty common for the same strings to be dynamically allocated repeatedly between applications and libraries, especially in circumstances where you could have multiple copies of a structure that allocates the string. So rather than duplicating and freeing these strings, you request a read-only pointer to an existing string and only incur the overhead of a hash lookup.

It sounds like micro-optimizing, but profiling has shown this can have a significant impact as you scale the number of copies up. It improves string creation/destruction speed, reduces memory use and decreases memory fragmentation, so a win all-around.

For more information, you can look at the Stringshare Tutorial.

Function Documentation

static Eina_Bool eina_stringshare_replace (const char ** p_str, const char * news) [inline, static]

Replace the previously stringshared pointer with a new content. The string pointed by p_str should be previously stringshared or NULL and it will be eina_stringshare_del(). The new string will be eina_stringshare_add() and then assigned to *p_str.

Parameters:

p_str pointer to the stringhare to be replaced. Must not be NULL, but *p_str may be NULL as it is a valid stringshare handle.
news new string to be stringshared, may be NULL.

Returns:

EINA_TRUE if the strings were different and thus replaced, EINA_FALSE if the strings were the same after shared.

EAPI const char * eina_stringshare_add_length (const char * str, unsigned int slen)

Retrieve an instance of a string for use in a program. Parameters:

str The string to retrieve an instance of.
slen The string size (<= strlen(str)).

Returns:

A pointer to an instance of the string on success. NULL on failure.

This function retrieves an instance of str. If str is NULL, then NULL is returned. If str is already stored, it is just returned and its reference counter is increased. Otherwise it is added to the strings to be searched and a duplicated string of str is returned.

This function does not check string size, but uses the give the exact given size. This can be used to stringshare part of a larger buffer or substring.

Note:

it's not possible to have more than 65k references or strings bigger than 65k since we use 'unsigned short' to save space.

See also:

eina_stringshare_add()

EAPI const char * eina_stringshare_add (const char * str)

Retrieve an instance of a string for use in a program. Parameters:

str The NULL terminated string to retrieve an instance of.

Returns:

A pointer to an instance of the string on success. NULL on failure.

This function retrieves an instance of str. If str is NULL, then NULL is returned. If str is already stored, it is just returned and its reference counter is increased. Otherwise it is added to the strings to be searched and a duplicated string of str is returned.

The string str must be NULL terminated ('\0') and its full length will be used. To use part of the string or non-null terminated, use eina_stringshare_add_length() instead.

Note:

it's not possible to have more than 65k references or strings bigger than 65k since we use 'unsigned short' to save space.

See also:

eina_stringshare_add_length()

EAPI const char * eina_stringshare_ref (const char * str)

Increment references of the given shared string. Parameters:

str The shared string.

Returns:

A pointer to an instance of the string on success. NULL on failure.

This is similar to eina_stringshare_add(), but it's faster since it will avoid lookups if possible, but on the down side it requires the parameter to be shared before, in other words, it must be the return of a previous eina_stringshare_add().

There is no unref since this is the work of eina_stringshare_del().

EAPI void eina_stringshare_del (const char * str)

Note that the given string has lost an instance. Parameters:

str string The given string.

This function decreases the reference counter associated to str if it exists. If that counter reaches 0, the memory associated to str is freed. If str is NULL, the function returns immediatly.

Note that if the given pointer is not shared or NULL, bad things will happen, likely a segmentation fault.

EAPI int eina_stringshare_strlen (const char * str)

Note that the given string must be shared. Parameters:

str the shared string to know the length. It is safe to give NULL, in that case -1 is returned.

This function is a cheap way to known the length of a shared string. Note that if the given pointer is not shared, bad things will happen, likely a segmentation fault. If in doubt, try strlen().

EAPI void eina_stringshare_dump (void)

Dump the contents of the stringshare. This function dumps all strings in the stringshare to stdout with a DDD: prefix per line and a memory usage summary.

Author

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