Monthly Archives: June 2012

Android garbage collection types

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We are all used to seeing lines like “D/dalvikvm( 8285): GC_CONCURRENT freed 494K, 9% free 14648K/16071K, paused 2ms+2ms” in the logcat, but what does the types mean (why is the device Garbage collecting just then)?

From the sources “dalvik/vm/alloc/Heap.h” we find that

typedef enum {
    /* Not enough space for an "ordinary" Object to be allocated. */
    GC_FOR_MALLOC,
    /* Automatic GC triggered by exceeding a heap occupancy threshold. */
    GC_CONCURRENT,
    /* Explicit GC via Runtime.gc(), VMRuntime.gc(), or SIGUSR1. */
    GC_EXPLICIT,
    /* GC to try to reduce heap footprint to allow more non-GC'ed memory. */
    GC_EXTERNAL_ALLOC,
    /* GC to dump heap contents to a file, only used under WITH_HPROF */
    GC_HPROF_DUMP_HEAP
} GcReason;

And a slightly more expanded explanation is:
GC_FOR_MALLOC was triggered because there wasn’t enough memory left on the heap to perform an allocation.

GC_EXPLICIT means that the garbage collector has been explicitly asked to collect.

GC_CONCURRENT Is triggered when the heap has reached a certain amount of objects to collect.

GC_EXTERNAL_ALLOC is triggered when the VM is trying to reduce the amount of memory used for collectable objects, to make room for more non-collectable.

Java safe conversion of float to int

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In most cases this is really not needed, if possible please keep the float as a float and work with it as such, but if needed the following works

public static Integer floatToInteger(float value){
    if (Math.round(value) < Integer.MIN_VALUE || Math.round(value) > Integer.MAX_VALUE) {
        throw new IllegalArgumentException
            (value + " cannot be cast to int without changing its value.");
    }
    return (int) Math.round(value);
}

(It might be needed for instance for a switch/case as that don’t work with float – or to work with external/legacy API’s that we can not or wish not to modify)