2898 // Multiple threads can race in this code but it's not possible to unmap small sections of

  2899 // virtual space to get requested alignment, like posix-like os's.

  2900 // Windows prevents multiple thread from remapping over each other so this loop is thread-safe.

  2901 char* os::reserve_memory_aligned(size_t size, size_t alignment) {

  2902   assert((alignment & (os::vm_allocation_granularity() - 1)) == 0,

  2903       "Alignment must be a multiple of allocation granularity (page size)");

  2904   assert((size & (alignment -1)) == 0, "size must be 'alignment' aligned");

  2905 

  2906   size_t extra_size = size + alignment;

  2907   assert(extra_size >= size, "overflow, size is too large to allow alignment");

  2908 

  2909   char* aligned_base = NULL;

  2910 

  2911   do {

  2912     char* extra_base = os::reserve_memory(extra_size, NULL, alignment);

  2913     if (extra_base == NULL) {

  2914       return NULL;

  2915     }

  2916     // Do manual alignment

  2917     aligned_base = (char*) align_size_up((uintptr_t) extra_base, alignment);

  2918 

  2919     os::release_memory(extra_base, extra_size);

  2920 

  2921     aligned_base = os::reserve_memory(size, aligned_base);

  2922 

  2923   } while (aligned_base == NULL);

  2924 

  2925   return aligned_base;

  2926 }

  2927