/*
* This is the default implementation of byte-sized cmpxchg. It emulates jbyte-sized cmpxchg
* in terms of jint-sized cmpxchg. Platforms may override this by defining their own inline definition
* as well as defining VM_HAS_SPECIALIZED_CMPXCHG_BYTE. This will cause the platform specific
* implementation to be used instead.
*/
inline jbyte Atomic::cmpxchg(jbyte exchange_value, volatile jbyte* dest,
jbyte compare_value, cmpxchg_memory_order order) {
STATIC_ASSERT(sizeof(jbyte) == 1);
volatile jint* dest_int =
static_cast<volatile jint*>(align_ptr_down(dest, sizeof(jint)));
size_t offset = pointer_delta(dest, dest_int, 1);
jint cur = *dest_int;
jbyte* cur_as_bytes = reinterpret_cast<jbyte*>(&cur);
// current value may not be what we are looking for, so force it
// to that value so the initial cmpxchg will fail if it is different
cur_as_bytes[offset] = compare_value;
// always execute a real cmpxchg so that we get the required memory
// barriers even on initial failure
do {
// value to swap in matches current value ...
jint new_value = cur;
// ... except for the one jbyte we want to update
reinterpret_cast<jbyte*>(&new_value)[offset] = exchange_value;
jint res = cmpxchg(new_value, dest_int, cur, order);
if (res == cur) break; // success
// at least one jbyte in the jint changed value, so update
// our view of the current jint
cur = res;
// if our jbyte is still as cur we loop and try again
} while (cur_as_bytes[offset] == compare_value);
return cur_as_bytes[offset];
}
void G1PageBasedVirtualSpace::commit_tail() {
vmassert(_tail_size > 0, "The size of the tail area must be > 0 when reaching here");
char* const aligned_end_address = (char*)align_ptr_down(_high_boundary, _page_size);
os::commit_memory_or_exit(aligned_end_address, _tail_size, os::vm_page_size(), _executable,
err_msg("Failed to commit tail area from " PTR_FORMAT " to " PTR_FORMAT " of length " SIZE_FORMAT ".",
p2i(aligned_end_address), p2i(_high_boundary), _tail_size));
}
