Eina_UStringshare_Group(3)

NAME
Eina_UStringshare_Group - Unicode Stringshare

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

SYNOPSIS

  Functions
static Eina_Bool eina_ustringshare_replace (const Eina_Unicode **p_str, const Eina_Unicode *news)
Replace the previously stringshared pointer with new content.
static Eina_Bool eina_ustringshare_replace_length (const Eina_Unicode **p_str, const Eina_Unicode *news, unsigned int slen)
Replace the previously stringshared pointer with a new content.
EINA_API const Eina_Unicode * eina_ustringshare_add_length (const Eina_Unicode *str, unsigned int slen)
Retrieves an instance of a string for use in a program.
EINA_API const Eina_Unicode * eina_ustringshare_add (const Eina_Unicode *str)
Retrieves an instance of a string for use in a program.
EINA_API const Eina_Unicode * eina_ustringshare_ref (const Eina_Unicode *str)
Increments references of the given shared string.
EINA_API void eina_ustringshare_del (const Eina_Unicode *str)
Notes that the given string has lost an instance.
EINA_API int eina_ustringshare_strlen (const Eina_Unicode *str)
Notes that the given string must be shared.
EINA_API void eina_ustringshare_dump (void)
Dumps the contents of the share_common.

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 UStringshare Tutorial.

Function Documentation

  static Eina_Bool eina_ustringshare_replace (const Eina_Unicode ** p_str, const Eina_Unicode * news) [inline], [static]

Replace the previously stringshared pointer with new content. The string pointed by p_str should be previously stringshared or NULL and it will be eina_ustringshare_del(). The new string will be passed to eina_ustringshare_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.

References EINA_FALSE, EINA_TRUE, eina_ustringshare_add(), and eina_ustringshare_del().

  static Eina_Bool eina_ustringshare_replace_length (const Eina_Unicode ** p_str, const Eina_Unicode * news, unsigned int slen) [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_ustringshare_del(). The new string will be passed to eina_ustringshare_add_length() 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.
    slen The string size (<= strlen(str)).

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

References EINA_FALSE, EINA_TRUE, eina_ustringshare_add_length(), and eina_ustringshare_del().

  EINA_API const Eina_Unicode* eina_ustringshare_add_length (const Eina_Unicode * str, unsigned int slen)

Retrieves 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 exact given size. This can be used to share_common part of a larger buffer or substring.

See also
    eina_ustringshare_add()

Referenced by eina_ustringshare_replace_length().

  EINA_API const Eina_Unicode* eina_ustringshare_add (const Eina_Unicode * str)

Retrieves 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.

See also
    eina_ustringshare_add_length()

Referenced by eina_ustringshare_replace().

  EINA_API const Eina_Unicode* eina_ustringshare_ref (const Eina_Unicode * str)

Increments 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_share_common_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_ustringshare_add().

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

  EINA_API void eina_ustringshare_del (const Eina_Unicode * str)

Notes 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 immediately.

Note
    If the given pointer is not shared, bad things will happen, likely a segmentation fault.

Referenced by eina_ustringshare_replace(), and eina_ustringshare_replace_length().

  EINA_API int eina_ustringshare_strlen (const Eina_Unicode * str)

Notes 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.

Returns
    The length of a shared string.

This function is a cheap way to known the length of a shared string.

Note
    If the given pointer is not shared, bad things will happen, likely a segmentation fault. If in doubt, try strlen().

  EINA_API void eina_ustringshare_dump (void)

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

Author

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