def test_fork_join():
logs = []
class Log(torch.autograd.Function):
@staticmethod
def forward(ctx, number, tensor):
ctx.number = number
return tensor.detach()
@staticmethod
def backward(ctx, grad):
logs.append(ctx.number)
return None, grad
a = torch.rand(1, device="cpu", requires_grad=True)
b = torch.rand(1, device="cuda", requires_grad=True)
a = Log.apply(1, a)
a, phony = fork(a)
b = join(a, phony)
b = Log.apply(2, b)
b = b.to("cpu")
(a + b).backward()
assert logs == [2, 1]
def test_join_when_fork_not_requires_grad():
x = torch.rand(2, 1)
a, b = x.chunk(2)
assert not a.requires_grad
a, p = fork(a)
assert not a.requires_grad
assert not p.requires_grad
assert not b.requires_grad
b = join(b, p)
assert not b.requires_grad
def test_serial_checkpoints(device):
# Copied from https://github.com/pytorch/pytorch/pull/18568.
timeline = []
class Log(torch.autograd.Function):
@staticmethod
def forward(ctx, name, x):
ctx.name = name
timeline.append(f"{name}:forward")
return x.detach()
@staticmethod
def backward(ctx, grad_output):
name = ctx.name
timeline.append(f"{name}:backward")
return None, grad_output
a = torch.rand(1, device=device, requires_grad=True)
b = torch.rand(1, device=device, requires_grad=True)
# Increase the next function sequence number.
_ = a + 1 + 2 + 3 + 4 + 5
a = checkpoint(partial(Log.apply, "a"), a)
a, phony = fork(a)
b = join(b, phony)
b = checkpoint(partial(Log.apply, "b"), b)
c = torch.cat((a, b))
out = c.sum()
# +--> {a} --Checkpoint(Log)--> {a}
# {out} --Sum--> {c} --Cat ^-----------------------------+
# +--> {b} --Checkpoint(Log)--> {b} --First--> {b}
out.backward()
assert timeline == [
"a:forward", "b:forward", "b:forward", "b:backward", "a:forward",
"a:backward"
]
def test_fork_join_no_grad(monkeypatch):
def do_not_apply(*args):
raise AssertionError("Function.apply called")
monkeypatch.setattr("torch.autograd.Function.apply", do_not_apply)
x = torch.rand(1, requires_grad=True)
with torch.no_grad():
x2, p = fork(x)
assert not p.requires_grad
assert x2 is x
x = x2
with torch.no_grad():
x2 = join(x, p)
assert x2 is x
x = x2
def test_fork_leak():
leak = None
class F(torch.autograd.Function):
@staticmethod
def forward(ctx, input):
return input
@staticmethod
def backward(ctx, grad):
nonlocal leak
leak = weakref.ref(ctx)
return grad
x = torch.rand(1, requires_grad=True)
x = F.apply(x)
x, phony = fork(x)
x = join(x, phony)
x.backward()
del x, phony
assert leak() is None
def test_fork_join_enable_grad():
x = torch.rand(1, requires_grad=True)
with torch.enable_grad():
x2, p = fork(x)
assert p.requires_grad
assert x2 is not x
x = x2
assert x.requires_grad
assert p.requires_grad
assert x.grad_fn.__class__ is Fork._backward_cls
assert p.grad_fn.__class__ is Fork._backward_cls
with torch.enable_grad():
x2 = join(x, p)
assert x2 is not x
x = x2
assert x.requires_grad
assert x.grad_fn.__class__ is Join._backward_cls
def test_blue_orange_not_requires_grad():
tensor1 = torch.rand(1, requires_grad=True)
tensor2 = torch.rand(1)
# Same with: output = tensor1*2 + tensor2
#
# +----------------------+
# | |
# tensor2 -- PortalBlue -+ +- PortalOrange -+
# | | |
# tensor1 ------------ Join -- Fork --- Mul --- Add -- output
#
main = tensor1
portal = Portal(tensor2, tensor_life=2)
phony = portal.blue()
main = join(main, phony)
main, phony = fork(main)
sub = portal.orange(phony)
output = main * 2 + sub
output.backward()
assert torch.allclose(tensor1.grad, torch.tensor([2.0]))
assert tensor2.grad is None