errors during run the codes provided in the paper

[byronwwang]

File.lua:141: Unwritable object at <?>.callback.closure.mnist.testdataset.createdataset.readlush.torch.cat

[byronwwang]

When I check the torchnet codes, I found that, in listdataset.lua, line 116, for different of list, it should be different. When list is a table, #self.list should be a number, but when list is LongTensor , #self.list is a tensor. Am I right? Maybe this caused the problem.

[lvdmaaten]

No this does look like a serialization issue that arises when you're creating the ParallelDatasetIterator. This creates a number of threads; at thread construction time, upvalues are serialized. Can you post a repro? Also, please make sure your threads package is up-to-date.

[ghost]

Hello,
I have the same issue when running on fresh Torch+Torchnet + dependencies install

Installed rocks:

argcheck: scm-1 (installed) - /home/x/torch/install/lib/luarocks/rocks
cwrap: scm-1 (installed) - /home/x/torch/install/lib/luarocks/rocks
dok: scm-1 (installed) - /home/x/torch/install/lib/luarocks/rocks
env: scm-1 (installed) - /home/x/torch/install/lib/luarocks/rocks
fftw3: scm-1 (installed) - /home/x/torch/install/lib/luarocks/rocks
gnuplot: scm-1 (installed) - /home/x/torch/install/lib/luarocks/rocks
graph: scm-1 (installed) - /home/x/torch/install/lib/luarocks/rocks
graphicsmagick: 1.scm-0 (installed) - /home/x/torch/install/lib/luarocks/rocks
image: 1.1.alpha-0 (installed) - /home/x/torch/install/lib/luarocks/rocks
lua-cjson: 2.1devel-1 (installed) - /home/x/torch/install/lib/luarocks/rocks
luaffi: scm-1 (installed) - /home/x/torch/install/lib/luarocks/rocks
luafilesystem: 1.6.3-2 (installed) - /home/x/torch/install/lib/luarocks/rocks
luasocket: 2.0rc1-2 (installed) - /home/x/torch/install/lib/luarocks/rocks
md5: 1.2-1 (installed) - /home/x/torch/install/lib/luarocks/rocks
mnist: scm-1 (installed) - /home/x/torch/install/lib/luarocks/rocks
nn: scm-1 (installed) - /home/x/torch/install/lib/luarocks/rocks
nngraph: scm-1 (installed) - /home/x/torch/install/lib/luarocks/rocks
nnx: 0.1-1 (installed) - /home/x/torch/install/lib/luarocks/rocks
optim: 1.0.5-0 (installed) - /home/x/torch/install/lib/luarocks/rocks
paths: scm-1 (installed) - /home/x/torch/install/lib/luarocks/rocks
penlight: scm-1 (installed) - /home/x/torch/install/lib/luarocks/rocks
qtlua: scm-1 (installed) - /home/x/torch/install/lib/luarocks/rocks
qttorch: scm-1 (installed) - /home/x/torch/install/lib/luarocks/rocks
signal: scm-1 (installed) - /home/x/torch/install/lib/luarocks/rocks
sundown: scm-1 (installed) - /home/x/torch/install/lib/luarocks/rocks
sys: 1.1-0 (installed) - /home/x/torch/install/lib/luarocks/rocks
tds: scm-1 (installed) - /home/x/torch/install/lib/luarocks/rocks
threads: scm-1 (installed) - /home/x/torch/install/lib/luarocks/rocks
torch: scm-1 (installed) - /home/x/torch/install/lib/luarocks/rocks
torchnet: scm-1 (installed) - /home/x/torch/install/lib/luarocks/rocks
trepl: scm-1 (installed) - /home/x/torch/install/lib/luarocks/rocks
xlua: 1.0-0 (installed) - /home/x/torch/install/lib/luarocks/rocks

[shreyshahi]

Hi, I am facing the same problem with ParallelDatasetIterator. I did a clean new install of torch and installed threads. Can any other library cause the serialization problem?

Is there something similar to pip freeze in Lua? It would be great if we can post the packages and their versions here.

[lvdmaaten]

Apparently, the mnist package is not serializable, perhaps because it contains objects that live in C-land, which is why you cannot do this. The solution is to not serialize the mnist object, by putting the content of loadmnist in the closure function (this way, the mnist package will be loaded inside each thread instead of being serialized).

[geogeorgiev]

As hinted by @byronwwang there is an actual bug in listdataset.lua, however, it is on line 126. When a torch.LongTensor is provided the assert statement fails with "

both (null) and torch.LongTensor have no less-equal operator"

.
The assert statement should be modified for the case of LongTensor by using :size(1) instead of #. The second option, which I am using, is to convert my list from LongTensor to Lua table with torch.totable()

[lvdmaaten]

@GooShan I think I fixed that bug a few minutes ago.

[lvdmaaten]

It appears the example in the paper was done for a different version of the mnist package. This code example should work fine:

local tnt   = require 'torchnet'

local function getIterator(mode)
  return tnt.ParallelDatasetIterator{
    nthread = 1,
    init    = function() require 'torchnet' end,
    closure = function()
      local mnist = require 'mnist'
      local dataset = mnist[mode .. 'dataset']()
      dataset.data = dataset.data:reshape(
         dataset.data:size(1),
         dataset.data:size(2) *
         dataset.data:size(3)
      ):double()
      return tnt.BatchDataset{
         batchsize = 128,
         dataset = tnt.ListDataset{
           list = torch.range(
             1, dataset.data:size(1)
           ):long(),
           load = function(idx)
             return {
               input  = dataset.data[idx],
               target = torch.LongTensor{
                 dataset.label[idx] + 1
               },
             } -- sample contains input and target
           end,
        }
      }
    end,
  }
end

local net = nn.Sequential():add(nn.Linear(784,10))

local engine = tnt.SGDEngine()
local meter  = tnt.AverageValueMeter()
local clerr  = tnt.ClassErrorMeter{topk = {1}}
engine.hooks.onStartEpoch = function(state)
  meter:reset()
  clerr:reset()
end
engine.hooks.onForwardCriterion =
function(state)
  meter:add(state.criterion.output)
  clerr:add(
    state.network.output, state.sample.target)
  print(string.format(
    'avg. loss: %2.4f; avg. error: %2.4f',
    meter:value(), clerr:value{k = 1}))
end

local criterion = nn.CrossEntropyCriterion()

engine:train{
  network   = net,
  iterator  = getIterator('train'),
  criterion = criterion,
  lr        = 0.1,
  maxepoch  = 10,
}
engine:test{
  network   = net,
  iterator  = getIterator('test'),
  criterion = criterion,
}

I will add it to the codebase.

[lvdmaaten]

See https://github.com/torchnet/torchnet/blob/master/example/mnist.lua for a working example with comments.