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().