def client_fork(t: Thread, b: bool, cell: Cell) -> None:
Requires(Acc(MayStart(t)))
Requires(getMethod(t) == Cell.incr)
Requires(Acc(cell.val))
Requires(cell is getArg(t, 0))
Ensures(getOld(t, arg(0).val) == 12)
Ensures(WaitLevel() < Level(t))
#:: ExpectedOutput(postcondition.violated:insufficient.permission)
Ensures(Acc(MayStart(t)))
cell.val = 12
t.start(decr, Cell.incr)
def thread_join_part_perm(t: Thread, cl: Cell) -> None:
Requires(getMethod(t) == decr)
Requires(getArg(t, 0) is cl)
Requires(getArg(t, 1) is 7)
Requires(getOld(t, arg(0).val) is 123)
Requires(Acc(ThreadPost(t), 1 / 2))
Requires(WaitLevel() < Level(t))
t.join(Cell.incr, decr)
assert cl.val == 116
#:: ExpectedOutput(assignment.failed:insufficient.permission)
cl.val = 11
def thread2(l: CellLock, c: Cell, secret: int) -> None:
Requires(Low(l) and l.get_locked() is c)
Requires(LowEvent() and WaitLevel() < Level(l))
while secret > 0:
# When writing TerminatesSif(e1, e2) as the last part of the invariant, Nagini does not check that the
# termination condition is low (which is the default), but instead checks that the loop terminates if e1 holds
# initially, using the ranking function e2. This is an alternative sufficient condition.
Invariant(TerminatesSif(True, secret))
secret -= 1
l.acquire()
c.leak = False
l.release()
def do_read(self, reader: Reader) -> None:
Requires(reader is not None)
Requires(Rd(self.lock) and Rd(self.c) and self.lock.get_locked() is self.c)
Requires(WaitLevel() < Level(self.lock))
Ensures(Rd(self.lock) and Rd(self.c))
self.lock.acquire()
self.c.rds += 1
#:: UnexpectedOutput(silicon)(lock.invariant.not.established:assertion.false,320)
self.lock.release()
reader.read(self.c)
self.lock.acquire()
self.c.rds -= 1
self.lock.release()
def do_write(self, writer: Writer) -> None:
Requires(writer is not None)
Requires(Rd(self.lock) and Rd(self.c) and self.lock.get_locked() is self.c)
Requires(WaitLevel() < Level(self.lock))
Ensures(Rd(self.lock) and Rd(self.c))
self.lock.acquire()
if self.c.rds != 0:
#:: UnexpectedOutput(silicon)(lock.invariant.not.established:assertion.false,320)
self.lock.release()
self.do_write(writer) # try again
else:
writer.write(self.c) # lock acquired successfully
self.lock.release()
def thread_join_pred_partial(t: Thread, cl: Cell) -> None:
Requires(getMethod(t) == decr_pred)
Requires(getArg(t, 0) is cl)
Requires(getArg(t, 1) is 7)
Requires(getOld(t, arg(0).val) is 123)
Requires(Acc(ThreadPost(t), 1 / 2))
Requires(WaitLevel() < Level(t))
Ensures(Joinable(t))
t.join(decr, decr_pred)
Unfold(Acc(cell_pred(cl, 116), 1 / 2))
assert cl.val == 116
#:: ExpectedOutput(unfold.failed:insufficient.permission)
Unfold(Acc(cell_pred(cl, 116), 1 / 2))
def thread_join_pred(t: Thread, cl: Cell) -> None:
Requires(getMethod(t) == decr_pred)
Requires(getArg(t, 0) is cl)
Requires(getArg(t, 1) is 7)
Requires(getOld(t, arg(0).val) is 123)
Requires(Acc(ThreadPost(t)))
Requires(WaitLevel() < Level(t))
Ensures(Joinable(t))
#:: ExpectedOutput(postcondition.violated:assertion.false)
Ensures(False)
t.join(decr, decr_pred)
Unfold(cell_pred(cl, 116))
assert cl.val == 116
def __init__(self,
locked_object: T,
above: Optional[BaseLock] = None,
below: Optional[BaseLock] = None) -> None:
"""
Create a lock whose level is below that of ``below`` and above that of ``above``,
which protects ``locked_object``.
Creating the lock "shares" the object (i.e., exhales the invariant).
Create subclasses of this class and override ``invariant`` to create a lock
with an invariant.
``Level(above)`` defaults to ``WaitLevel()``.
"""
Requires(MustTerminate(1))
Requires(
Implies(above is None and below is not None,
WaitLevel() < Level(below)))
Requires(
Implies(above is not None and below is not None,
Level(above) < Level(below)))
Requires(self.invariant())
Ensures(Implies(above is None, WaitLevel() < Level(self)))
Ensures(Implies(above is not None, Level(above) < Level(self)))
Ensures(Implies(below is not None, Level(self) < Level(below)))
def do_a_thing(self) -> None:
Requires(Rd(self.l) and Rd(self.c) and self.l.get_locked() is self.c)
Requires(WaitLevel() < Level(self.l))
Ensures(Rd(self.l) and Rd(self.c))
#:: ExpectedOutput(postcondition.violated:assertion.false)|MissingOutput(postcondition.violated:assertion.false, 320)
Ensures(False)
self.l.acquire()
self.c.n += 1
#:: UnexpectedOutput(silicon)(lock.invariant.not.established:assertion.false, 320)
self.l.release()
self.need_value()
t1 = Thread(None, self.need_value, args=())
t2 = Thread(None, self.need_value, args=())
t1.start(self.need_value)
t2.start(self.need_value)
t1.join(self.need_value)
t2.join(self.need_value)
#:: ExpectedOutput(carbon)(assert.failed:assertion.false)
Assert(False) # Carbon does not terminate for the next statement
self.need_value()
self.l.acquire()
self.c.n -= 1
self.l.release()
def __init__(self, c: Cell) -> None:
Requires(Acc(c.rds) and Acc(c.value) and c.rds == 0)
Ensures(Acc(self.c) and self.c == c and Acc(self.lock) and self.lock.get_locked() is self.c)
Ensures(WaitLevel() < Level(self.lock))
self.c = c # type: Cell
self.lock = CellLock(self.c) # type: CellLock
def do_a_thing_5(self) -> None:
Requires(Rd(self.l) and Rd(self.c) and self.l.get_locked() is self.c)
Requires(WaitLevel() < Level(self.l))
Ensures(Rd(self.l) and Rd(self.c))
self.l.acquire()
self.c.value += 2
def __init__(self) -> None:
self.c = Cell(12)
self.c.value = 14
self.l = CellLock(self.c)
Ensures(Acc(self.c) and Acc(self.l) and self.l.get_locked() is self.c)
Ensures(WaitLevel() < Level(self.l))
def thread_join_minimal(t: Thread, cl: Cell) -> None:
Requires(Joinable(t))
Requires(WaitLevel() < Level(t))
t.join(Cell.incr, decr)
#:: ExpectedOutput(assert.failed:insufficient.permission)
assert cl.val == 116