atomiclong.py

from cffi import FFI

from functools import total_ordering

ffi = FFI()

ffi.cdef("""
long long_add_and_fetch(long *, long);
long long_sub_and_fetch(long *, long);
long long_bool_compare_and_swap(long *, long, long);
""")

lib = ffi.verify("""
long long_add_and_fetch(long *v, long l) {
    return __sync_add_and_fetch(v, l);
};

long long_sub_and_fetch(long *v, long l) {
    return __sync_sub_and_fetch(v, l);
};

long long_bool_compare_and_swap(long *v, long o, long n) {
    return __sync_bool_compare_and_swap(v, o, n);
};
""")


@total_ordering
class AtomicLong(object):
    def __init__(self, initial_value):
        self._storage = ffi.new('long *', initial_value)

    def __repr__(self):
        return '<{0} at 0x{1:x}: {2!r}>'.format(
            self.__class__.__name__, id(self), self.value)

    @property
    def value(self):
        return self._storage[0]

    @value.setter
    def value(self, new):
        lib.long_bool_compare_and_swap(self._storage, self.value, new)

    def __iadd__(self, inc):
        lib.long_add_and_fetch(self._storage, inc)
        return self

    def __isub__(self, dec):
        lib.long_sub_and_fetch(self._storage, dec)
        return self

    def __eq__(self, other):
        # This is needed because between `self.value` and `other.value` being
        # evaluated it's possible for the value to be changed (and since this
        # is a library predicated on threads being a thing, we have to care
        # about such rare race conditions)
        if self is other:
            return True
        elif isinstance(other, AtomicLong):
            return self.value == other.value
        else:
            return self.value == other

    def __ne__(self, other):
        return not (self == other)

    def __lt__(self, other):
        # See __eq__ for an explanation of why this is a thing.
        if self is other:
            return False
        elif isinstance(other, AtomicLong):
            return self.value < other.value
        else:
            return self.value < other