diff -r 89d6a7a84779 -r 25a17d01db0c Symbian3/PDK/Source/GUID-3D10DAFD-BE83-4892-B5E0-2ED7CF047788.dita --- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/Symbian3/PDK/Source/GUID-3D10DAFD-BE83-4892-B5E0-2ED7CF047788.dita Fri Jan 22 18:26:19 2010 +0000 @@ -0,0 +1,72 @@ + + + + + +UHEAP +Markers and Panics in GLib-based ApplicationsThe 2.10.x version of GLib has introduced a new type of memory +allocator called slice allocator. These allocators allocate memory in page +sizes even for a small request of something like 20 bytes. Once a huge chunk +has been allocated, all the future memory requests are granted using the chunk +that was allocated for the first memory request. Once the free pool runs out, +another huge chunk is allocated. +

Whenever the memory is freed using g_slice_free1(), the +memory is not returned to the OS; instead it is maintained by GLib as free +memory which is used to for future memory requests.

+

The following example explains the issue. The code given below uses slice +allocators to allocate 10 bytes of memory using g_slice_alloc() and +subsequently frees it using g_slice_free1(). The code panics +at __UHEAP_MARKEND, although the memory that has been allocated +has been deallocated. This is because all the allocated memory on the heap +has not been deallocated. When the user calls g_slice_free1() to +free up, the memory is not freed; instead, GLib will keep it as part of the +free pool for future allocation.

+#include <glib.h> +#include <e32base.h> + +int main() +{ + char *x; + __UHEAP_MARK; + x = (char *)g_slice_alloc(10); + g_slice_free1(10,x); + __UHEAP_MARKEND; + return 0; +} + +

To get around this problem, define an environment variable G_SLICE and +set it to “always-malloc”.

+It is necessary that this environment variable is set before any GLib +call that can cause memory allocation. If the environment variable is set +after any g_slice* APIs have been called either from the +application code or from GLib library code, setting it has not effect. +

The code below demonstrates the usage.

+#include <glib.h> +#include <e32base.h> + +int main() +{ + char *x; + __UHEAP_MARK; + g_setenv("G_SLICE","always-malloc",1); + x = (char *)g_slice_alloc(10); + g_slice_free1(10,x); + __UHEAP_MARKEND; + return 0; +} + +G_SLICE is just a debugging environment variable. Setting +it to “always-malloc” can help in detecting memory leaks in application code. +This setting need not and should not be done in the release code since doing +it overrides the GLib memory allocation mechanism and hence may +result in loss of efficiency. The slice allocators are used by other GLib +APIs like GList, GSList, GNode, +and so on. Thus setting the environment variable is necessary if the application +makes use of any such APIs that might use slice allocators. + \ No newline at end of file