Android 虚拟机中的内存分配与OOM问题详解

 <application
    android:largeHeap="true">
    ...
</application>

//ActivityManager的getMemoryClass()获得内用正常情况下内存的大小，即heapgrowthlimit的值
//ActivityManager的getLargeMemoryClass()可以获得开启largeHeap最大的内存大小，即heapsize的指
ActivityManager activityManager = (ActivityManager)context.getSystemService(Context.ACTIVITY_SERVICE);
activityManager.getMemoryClass();
activityManager.getLargeMemoryClass();

/* Try as hard as possible to allocate some memory.
 */
static void *tryMalloc(size_t size)
{
    void *ptr;
//TODO: figure out better heuristics
//    There will be a lot of churn if someone allocates a bunch of
//    big objects in a row, and we hit the frag case each time.
//    A full GC for each.
//    Maybe we grow the heap in bigger leaps
//    Maybe we skip the GC if the size is large and we did one recently
//      (number of allocations ago) (watch for thread effects)
//    DeflateTest allocs a bunch of ~128k buffers w/in 0-5 allocs of each other
//      (or, at least, there are only 0-5 objects swept each time)
    ptr = dvmHeapSourceAlloc(size);
    if (ptr != NULL) {
        return ptr;
    }
    /*
     * The allocation failed.  If the GC is running, block until it
     * completes and retry.
     */
    if (gDvm.gcHeap->gcRunning) {
        /*
         * The GC is concurrently tracing the heap.  Release the heap
         * lock, wait for the GC to complete, and retrying allocating.
         */
        dvmWaitForConcurrentGcToComplete();
    } else {
      /*
       * Try a foreground GC since a concurrent GC is not currently running.
       */
      gcForMalloc(false);
    }
    ptr = dvmHeapSourceAlloc(size);
    if (ptr != NULL) {
        return ptr;
    }
    /* Even that didn't work;  this is an exceptional state.
     * Try harder, growing the heap if necessary.
     */
    ptr = dvmHeapSourceAllocAndGrow(size);
    if (ptr != NULL) {
        size_t newHeapSize;
        newHeapSize = dvmHeapSourceGetIdealFootprint();
//TODO: may want to grow a little bit more so that the amount of free
//      space is equal to the old free space   the utilization slop for
//      the new allocation.
        LOGI_HEAP("Grow heap (frag case) to "
                "%zu.zuMB for %zu-byte allocation",
                FRACTIONAL_MB(newHeapSize), size);
        return ptr;
    }
    /* Most allocations should have succeeded by now, so the heap
     * is really full, really fragmented, or the requested size is
     * really big.  Do another GC, collecting SoftReferences this
     * time.  The VM spec requires that all SoftReferences have
     * been collected and cleared before throwing an OOME.
     */
//TODO: wait for the finalizers from the previous GC to finish
    LOGI_HEAP("Forcing collection of SoftReferences for %zu-byte allocation",
            size);
    gcForMalloc(true);
    ptr = dvmHeapSourceAllocAndGrow(size);
    if (ptr != NULL) {
        return ptr;
    }
//TODO: maybe wait for finalizers and try one last time
    LOGE_HEAP("Out of memory on a %zd-byte allocation.", size);
//TODO: tell the HeapSource to dump its state
    dvmDumpThread(dvmThreadSelf(), false);
    return NULL;
}