Introduction -to GLib Low Memory Handler

Memory allocation failures are more likely on a mobile device and aborting -the application in such cases is undesirable. Therefore, the implementation -of GLib for Symbian platform has been modified so that the GLib memory allocation -APIs return NULL and do not call abort(). This requires the -application written using GLib to start handling memory allocation failures -which they are currently not doing.

If the user, for example, wants to change the first character of a string -with z and return the string to the caller a GLib code for this can be written -as follows:

If there is a memory allocation failure in Linux, the call to g_strdup which -internally uses g_malloc will cause the application to abort. -However, in Symbian platform the g_malloc() function will -return NULL, but the implementation of g_strdup() is such -that the return value of g_malloc() is not checked for NULL. -This causes the g_strdup() API to panic or crash the application. -Thus, a mechanism to deal with the failures, panics or crash resulting from -low memory situations within Symbian platform is needed.

Illustration -of the mechanism to handle a memory allocation failure scenario -

The user needs to initialize the framework which handles the low memory -scenarios using the below-mentioned macros:

SET_LOW_MEMORY_TRAP(failure_value): This -macro will set a trap handler for low memory cases. In case there is an allocation -failure, the failure value will be returned from the function where the trap -handler is set.
SET_LOW_MEMORY_TRAP_VOID(): This -will do the same as the above except that the function where this is set will -just return. This will typically be used by functions which return void. In -this case, however, the caller must check the errno value. -If it is ENOMEM, then the user must handle things appropriately.
REMOVE_LOW_MEMORY_TRAP(): This -will remove the trap handler which was set.

The function f1() will now be rewritten as:

#include <glowmem> -gchar * f1(gchar * x) -{ - gchar *temp; - SET_LOW_MEMORY_TRAP(NULL); - temp = g_strdup(x); - temp[0] = ‘z’; - REMOVE_LOW_MEMORY_TRAP(): - return temp; -}

If there is a memory allocation failure when the above function f1() is -called, then f1() will return NULL to its caller. The caller -of f1() is expected to check the failure value of f1() instead -of ignoring the same.

Some words of caution: The -macro SET_LOW_MEMORY_TRAP() defines a variable so it is necessary -to make the call after all the local variables declarations in C. REMOVE_LOW_MEMORY_TRAP() must -be called just before the return from the function, which means that if there -are four return statements in the function then all of them must be preceded -with a call to REMOVE_LOW_MEMORY_TRAP().