ir connected 
white objects as gray and turning themselves black. 
Every M allocs, it will pause for a sweep where it makes sure 
all grays are marked black and io_frees all whites.
<p>
If the sweepsPerGeneration is set to zero, it will immediately mark 
all blacks as white again and mark the root objects as gray. Otherwise, 
it will wait until the sweepsPerGeneration count is reached to do this. 
By adjusting the allocsPerSweep and sweepsPerGeneration appropriately, the 
collector can be tuned efficiently 