# Copyright (c) Facebook, Inc. and its affiliates.
#
# This source code is licensed under the MIT license found in the
# LICENSE file in the root directory of this source tree.
import math
from typing import Dict, List, Optional
import sys
import torch
import torch.nn as nn
from fairseq import search, utils
from fairseq.models import FairseqIncrementalDecoder
from torch import Tensor
from fairseq.ngram_repeat_block import NGramRepeatBlock
from data import data_utils
class SequenceGenerator(nn.Module):
def __init__(
self,
models,
tgt_dict,
beam_size=1,
max_len_a=0,
max_len_b=200,
max_len=0,
min_len=1,
normalize_scores=True,
len_penalty=1.0,
unk_penalty=0.0,
temperature=1.0,
match_source_len=False,
no_repeat_ngram_size=0,
search_strategy=None,
eos=None,
symbols_to_strip_from_output=None,
lm_model=None,
lm_weight=1.0,
constraint_trie=None,
constraint_range=None,
gen_code=False,
gen_box=False,
ignore_eos=False,
zero_shot=False
):
"""Generates translations of a given source sentence.
Args:
models (List[~fairseq.models.FairseqModel]): ensemble of models,
currently support fairseq.models.TransformerModel for scripting
beam_size (int, optional): beam width (default: 1)
max_len_a/b (int, optional): generate sequences of maximum length
ax + b, where x is the source length
max_len (int, optional): the maximum length of the generated output
(not including end-of-sentence)
min_len (int, optional): the minimum length of the generated output
(not including end-of-sentence)
normalize_scores (bool, optional): normalize scores by the length
of the output (default: True)
len_penalty (float, optional): length penalty, where <1.0 favors
shorter, >1.0 favors longer sentences (default: 1.0)
unk_penalty (float, optional): unknown word penalty, where <0
produces more unks, >0 produces fewer (default: 0.0)
temperature (float, optional): temperature, where values
>1.0 produce more uniform samples and values <1.0 produce
sharper samples (default: 1.0)
match_source_len (bool, optional): outputs should match the source
length (default: False)
"""
super().__init__()
if isinstance(models, EnsembleModel):
self.model = models
else:
self.model = EnsembleModel(models)
self.gen_code = gen_code
self.gen_box = gen_box
self.ignore_eos = ignore_eos
self.tgt_dict = tgt_dict
self.pad = tgt_dict.pad()
self.unk = tgt_dict.unk()
self.bos = tgt_dict.bos()
self.eos = tgt_dict.eos() if eos is None else eos
self.symbols_to_strip_from_output = (
symbols_to_strip_from_output.union({self.eos})
if symbols_to_strip_from_output is not None
else {self.bos, self.eos}
)
self.vocab_size = len(tgt_dict)
self.beam_size = beam_size
# the max beam size is the dictionary size - 1, since we never select pad
self.beam_size = min(beam_size, self.vocab_size - 1)
self.max_len_a = max_len_a
self.max_len_b = max_len_b
self.min_len = min_len
self.max_len = max_len or self.model.max_decoder_positions()
self.normalize_scores = normalize_scores
self.len_penalty = len_penalty
self.unk_penalty = unk_penalty
self.temperature = temperature
self.match_source_len = match_source_len
self.zero_shot = zero_shot
if no_repeat_ngram_size > 0:
self.repeat_ngram_blocker = NGramRepeatBlock(no_repeat_ngram_size)
else:
self.repeat_ngram_blocker = None
assert temperature > 0, "--temperature must be greater than 0"
self.search = (
search.BeamSearch(tgt_dict) if search_strategy is None else search_strategy
)
# We only need to set src_lengths in LengthConstrainedBeamSearch.
# As a module attribute, setting it would break in multithread
# settings when the model is shared.
self.should_set_src_lengths = (
hasattr(self.search, "needs_src_lengths") and self.search.needs_src_lengths
)
self.model.eval()
self.lm_model = lm_model
self.lm_weight = lm_weight
if self.lm_model is not None:
self.lm_model.eval()
self.constraint_trie = constraint_trie
self.constraint_start = None
self.constraint_end = None
if constraint_range is not None:
constraint_start, constraint_end = constraint_range.split(',')
self.constraint_start = int(constraint_start)
self.constraint_end = int(constraint_end)
def cuda(self):
self.model.cuda()
return self
@torch.no_grad()
def forward(
self,
sample: Dict[str, Dict[str, Tensor]],
prefix_tokens: Optional[Tensor] = None,
bos_token: Optional[int] = None,
):
"""Generate a batch of translations.
Args:
sample (dict): batch
prefix_tokens (torch.LongTensor, optional): force decoder to begin
with these tokens
bos_token (int, optional): beginning of sentence token
(default: self.eos)
"""
return self._generate(sample, prefix_tokens, bos_token=bos_token)
# TODO(myleott): unused, deprecate after pytorch-translate migration
def generate_batched_itr(self, data_itr, beam_size=None, cuda=False, timer=None):
"""Iterate over a batched dataset and yield individual translations.
Args:
cuda (bool, optional): use GPU for generation
timer (StopwatchMeter, optional): time generations
"""
for sample in data_itr:
s = utils.move_to_cuda(sample) if cuda else sample
if "net_input" not in s:
continue
input = s["net_input"]
# model.forward normally channels prev_output_tokens into the decoder
# separately, but SequenceGenerator directly calls model.encoder
encoder_input = {
k: v for k, v in input.items() if k != "prev_output_tokens"
}
if timer is not None:
timer.start()
with torch.no_grad():
hypos = self.generate(encoder_input)
if timer is not None:
timer.stop(sum(len(h[0]["tokens"]) for h in hypos))
for i, id in enumerate(s["id"].data):
# remove padding
src = utils.strip_pad(input["src_tokens"].data[i, :], self.pad)
ref = (
utils.strip_pad(s["target"].data[i, :], self.pad)
if s["target"] is not None
else None
)
yield id, src, ref, hypos[i]
@torch.no_grad()
def generate(self, models, sample: Dict[str, Dict[str, Tensor]], **kwargs) -> List[List[Dict[str, Tensor]]]:
"""Generate translations. Match the api of other fairseq generators.
Args:
models (List[~fairseq.models.FairseqModel]): ensemble of models
sample (dict): batch
prefix_tokens (torch.LongTensor, optional): force decoder to begin
with these tokens
constraints (torch.LongTensor, optional): force decoder to include
the list of constraints
bos_token (int, optional): beginning of sentence token
(default: self.eos)
"""
return self._generate(models, sample, **kwargs)
def _generate(
self,
models,
sample: Dict[str, Dict[str, Tensor]],
prefix_tokens: Optional[Tensor] = None,
constraints: Optional[Tensor] = None,
bos_token: Optional[int] = None,
):
model = EnsembleModel(models)
incremental_states = torch.jit.annotate(
List[Dict[str, Dict[str, Optional[Tensor]]]],
[
torch.jit.annotate(Dict[str, Dict[str, Optional[Tensor]]], {})
for i in range(model.models_size)
],
)
net_input = sample["net_input"]
if "src_tokens" in net_input:
src_tokens = net_input["src_tokens"]
# length of the source text being the character length except EndOfSentence and pad
src_lengths = (
(src_tokens.ne(self.eos) & src_tokens.ne(self.pad)).long().sum(dim=1)
)
elif "source" in net_input:
src_tokens = net_input["source"]
src_lengths = (
net_input["padding_mask"].size(-1) - net_input["padding_mask"].sum(-1)
if net_input["padding_mask"] is not None
else torch.tensor(src_tokens.size(-1)).to(src_tokens)
)
elif "features" in net_input:
src_tokens = net_input["features"]
src_lengths = (
net_input["padding_mask"].size(-1) - net_input["padding_mask"].sum(-1)
if net_input["padding_mask"] is not None
else torch.tensor(src_tokens.size(-1)).to(src_tokens)
)
else:
raise Exception("expected src_tokens or source in net input. input keys: " + str(net_input.keys()))
# bsz: total number of sentences in beam
# Note that src_tokens may have more than 2 dimensions (i.e. audio features)
bsz, src_len = src_tokens.size()[:2]
beam_size = self.beam_size
if constraints is not None and not self.search.supports_constraints:
raise NotImplementedError(
"Target-side constraints were provided, but search method doesn't support them"
)
# Initialize constraints, when active
self.search.init_constraints(constraints, beam_size)
max_len: int = -1
if self.match_source_len:
max_len = src_lengths.max().item()
else:
max_len = int(self.max_len_a * src_len + self.max_len_b)
assert (
self.min_len <= max_len
), "min_len cannot be larger than max_len, please adjust these!"
# compute the encoder output for each beam
with torch.autograd.profiler.record_function("EnsembleModel: forward_encoder"):
encoder_outs = model.forward_encoder(net_input)
# placeholder of indices for bsz * beam_size to hold tokens and accumulative scores
new_order = torch.arange(bsz).view(-1, 1).repeat(1, beam_size).view(-1)
new_order = new_order.to(src_tokens.device).long()
encoder_outs = model.reorder_encoder_out(encoder_outs, new_order)
# ensure encoder_outs is a List.
assert encoder_outs is not None
# initialize buffers
scores = (
torch.zeros(bsz * beam_size, max_len + 1).to(src_tokens).float()
) # +1 for eos; pad is never chosen for scoring
tokens = (
torch.zeros(bsz * beam_size, max_len + 2)
.to(src_tokens)
.long()
.fill_(self.pad)
) # +2 for eos and pad
# tokens[:, 0] = self.eos if bos_token is None else bos_token
tokens[:, 0] = self.bos
attn: Optional[Tensor] = None
# A list that indicates candidates that should be ignored.
# For example, suppose we're sampling and have already finalized 2/5
# samples. Then cands_to_ignore would mark 2 positions as being ignored,
# so that we only finalize the remaining 3 samples.
cands_to_ignore = (
torch.zeros(bsz, beam_size).to(src_tokens).eq(-1)
) # forward and backward-compatible False mask
# list of completed sentences
finalized = torch.jit.annotate(
List[List[Dict[str, Tensor]]],
[torch.jit.annotate(List[Dict[str, Tensor]], []) for i in range(bsz)],
) # contains lists of dictionaries of infomation about the hypothesis being finalized at each step
# a boolean array indicating if the sentence at the index is finished or not
finished = [False for i in range(bsz)]
num_remaining_sent = bsz # number of sentences remaining
# number of candidate hypos per step
cand_size = 2 * beam_size # 2 x beam size in case half are EOS
# offset arrays for converting between different indexing schemes
bbsz_offsets = (
(torch.arange(0, bsz) * beam_size)
.unsqueeze(1)
.type_as(tokens)
.to(src_tokens.device)
)
cand_offsets = torch.arange(0, cand_size).type_as(tokens).to(src_tokens.device)
reorder_state: Optional[Tensor] = None
batch_idxs: Optional[Tensor] = None
original_batch_idxs: Optional[Tensor] = None
if "id" in sample and isinstance(sample["id"], Tensor):
original_batch_idxs = sample["id"]
else:
original_batch_idxs = torch.arange(0, bsz).type_as(tokens)
for step in range(max_len + 1): # one extra step for EOS marker
# reorder decoder internal states based on the prev choice of beams
if reorder_state is not None:
if batch_idxs is not None:
# update beam indices to take into account removed sentences
corr = batch_idxs - torch.arange(batch_idxs.numel()).type_as(
batch_idxs
)
reorder_state.view(-1, beam_size).add_(
corr.unsqueeze(-1) * beam_size
)
original_batch_idxs = original_batch_idxs[batch_idxs]
model.reorder_incremental_state(incremental_states, reorder_state)
encoder_outs = model.reorder_encoder_out(
encoder_outs, reorder_state
)
with torch.autograd.profiler.record_function("EnsembleModel: forward_decoder"):
lprobs, avg_attn_scores = model.forward_decoder(
tokens[:, : step + 1],
encoder_outs,
incremental_states,
self.temperature,
constraint_trie=self.constraint_trie,
constraint_start=self.constraint_start,
constraint_end=self.constraint_end,
gen_code=self.gen_code,
zero_shot=self.zero_shot,
prefix_tokens=prefix_tokens
)
if self.lm_model is not None:
lm_out = self.lm_model(tokens[:, : step + 1])
probs = self.lm_model.get_normalized_probs(
lm_out, log_probs=True, sample=None
)
probs = probs[:, -1, :] * self.lm_weight
lprobs += probs
# handle prefix tokens (possibly with different lengths)
if (
prefix_tokens is not None
and step < prefix_tokens.size(1)
and step < max_len
):
lprobs, tokens, scores = self._prefix_tokens(
step, lprobs, scores, tokens, prefix_tokens, beam_size
)
elif step < self.min_len:
# minimum length constraint (does not apply if using prefix_tokens)
lprobs[:, self.eos] = -math.inf
lprobs[lprobs != lprobs] = torch.tensor(-math.inf).to(lprobs)
lprobs[:, self.pad] = -math.inf # never select pad
lprobs[:, self.unk] -= self.unk_penalty # apply unk penalty
if (self.gen_code or self.gen_box) and step < max_len:
lprobs[:, :4] = -math.inf
if self.gen_box:
lprobs[:, -1] = -math.inf
if (step + 1) % 5 == 0:
lprobs[:, self.constraint_start:59457] = -math.inf
else:
lprobs[:, 59457:] = -math.inf
# handle max length constraint
if step >= max_len:
lprobs[:, : self.eos] = -math.inf
lprobs[:, self.eos + 1 :] = -math.inf
if self.ignore_eos:
lprobs[:, self.eos] = 1
# Record attention scores, only support avg_attn_scores is a Tensor
if avg_attn_scores is not None:
if attn is None:
attn = torch.empty(
bsz * beam_size, avg_attn_scores.size(1), max_len + 2
).to(scores)
attn[:, :, step + 1].copy_(avg_attn_scores)
scores = scores.type_as(lprobs)
eos_bbsz_idx = torch.empty(0).to(
tokens
) # indices of hypothesis ending with eos (finished sentences)
eos_scores = torch.empty(0).to(
scores
) # scores of hypothesis ending with eos (finished sentences)
if self.should_set_src_lengths:
self.search.set_src_lengths(src_lengths)
if self.repeat_ngram_blocker is not None:
lprobs = self.repeat_ngram_blocker(tokens, lprobs, bsz, beam_size, step)
# Shape: (batch, cand_size)
cand_scores, cand_indices, cand_beams = self.search.step(
step,
lprobs.view(bsz, -1, self.vocab_size),
scores.view(bsz, beam_size, -1)[:, :, :step],
tokens[:, : step + 1],
original_batch_idxs,
)
# cand_bbsz_idx contains beam indices for the top candidate
# hypotheses, with a range of values: [0, bsz*beam_size),
# and dimensions: [bsz, cand_size]
cand_bbsz_idx = cand_beams.add(bbsz_offsets)
# finalize hypotheses that end in eos
# Shape of eos_mask: (batch size, beam size)
eos_mask = cand_indices.eq(self.eos) & cand_scores.ne(-math.inf)
eos_mask[:, :beam_size][cands_to_ignore] = torch.tensor(0).to(eos_mask)
# only consider eos when it's among the top beam_size indices
# Now we know what beam item(s) to finish
# Shape: 1d list of absolute-numbered
eos_bbsz_idx = torch.masked_select(
cand_bbsz_idx[:, :beam_size], mask=eos_mask[:, :beam_size]
)
finalized_sents: List[int] = []
if eos_bbsz_idx.numel() > 0:
eos_scores = torch.masked_select(
cand_scores[:, :beam_size], mask=eos_mask[:, :beam_size]
)
finalized_sents = self.finalize_hypos(
step,
eos_bbsz_idx,
eos_scores,
tokens,
scores,
finalized,
finished,
beam_size,
attn,
src_lengths,
max_len,
)
num_remaining_sent -= len(finalized_sents)
assert num_remaining_sent >= 0
if num_remaining_sent == 0:
break
if self.search.stop_on_max_len and step >= max_len:
break
assert step < max_len, f"{step} < {max_len}"
# Remove finalized sentences (ones for which {beam_size}
# finished hypotheses have been generated) from the batch.
if len(finalized_sents) > 0:
new_bsz = bsz - len(finalized_sents)
# construct batch_idxs which holds indices of batches to keep for the next pass
batch_mask = torch.ones(
bsz, dtype=torch.bool, device=cand_indices.device
)
batch_mask[finalized_sents] = False
# TODO replace `nonzero(as_tuple=False)` after TorchScript supports it
batch_idxs = torch.arange(
bsz, device=cand_indices.device
).masked_select(batch_mask)
# Choose the subset of the hypothesized constraints that will continue
self.search.prune_sentences(batch_idxs)
eos_mask = eos_mask[batch_idxs]
cand_beams = cand_beams[batch_idxs]
bbsz_offsets.resize_(new_bsz, 1)
cand_bbsz_idx = cand_beams.add(bbsz_offsets)
cand_scores = cand_scores[batch_idxs]
cand_indices = cand_indices[batch_idxs]
if prefix_tokens is not None:
prefix_tokens = prefix_tokens[batch_idxs]
src_lengths = src_lengths[batch_idxs]
cands_to_ignore = cands_to_ignore[batch_idxs]
scores = scores.view(bsz, -1)[batch_idxs].view(new_bsz * beam_size, -1)
tokens = tokens.view(bsz, -1)[batch_idxs].view(new_bsz * beam_size, -1)
if attn is not None:
attn = attn.view(bsz, -1)[batch_idxs].view(
new_bsz * beam_size, attn.size(1), -1
)
bsz = new_bsz
else:
batch_idxs = None
# Set active_mask so that values > cand_size indicate eos hypos
# and values < cand_size indicate candidate active hypos.
# After, the min values per row are the top candidate active hypos
# Rewrite the operator since the element wise or is not supported in torchscript.
eos_mask[:, :beam_size] = ~((~cands_to_ignore) & (~eos_mask[:, :beam_size]))
active_mask = torch.add(
eos_mask.type_as(cand_offsets) * cand_size,
cand_offsets[: eos_mask.size(1)],
)
# get the top beam_size active hypotheses, which are just
# the hypos with the smallest values in active_mask.
# {active_hypos} indicates which {beam_size} hypotheses
# from the list of {2 * beam_size} candidates were
# selected. Shapes: (batch size, beam size)
new_cands_to_ignore, active_hypos = torch.topk(
active_mask, k=beam_size, dim=1, largest=False
)
# update cands_to_ignore to ignore any finalized hypos.
cands_to_ignore = new_cands_to_ignore.ge(cand_size)[:, :beam_size]
# Make sure there is at least one active item for each sentence in the batch.
assert (~cands_to_ignore).any(dim=1).all()
# update cands_to_ignore to ignore any finalized hypos
# {active_bbsz_idx} denotes which beam number is continued for each new hypothesis (a beam
# can be selected more than once).
active_bbsz_idx = torch.gather(cand_bbsz_idx, dim=1, index=active_hypos)
active_scores = torch.gather(cand_scores, dim=1, index=active_hypos)
active_bbsz_idx = active_bbsz_idx.view(-1)
active_scores = active_scores.view(-1)
# copy tokens and scores for active hypotheses
# Set the tokens for each beam (can select the same row more than once)
tokens[:, : step + 1] = torch.index_select(
tokens[:, : step + 1], dim=0, index=active_bbsz_idx
)
# Select the next token for each of them
tokens.view(bsz, beam_size, -1)[:, :, step + 1] = torch.gather(
cand_indices, dim=1, index=active_hypos
)
if step > 0:
scores[:, :step] = torch.index_select(
scores[:, :step], dim=0, index=active_bbsz_idx
)
scores.view(bsz, beam_size, -1)[:, :, step] = torch.gather(
cand_scores, dim=1, index=active_hypos
)
# Update constraints based on which candidates were selected for the next beam
self.search.update_constraints(active_hypos)
# copy attention for active hypotheses
if attn is not None:
attn[:, :, : step + 2] = torch.index_select(
attn[:, :, : step + 2], dim=0, index=active_bbsz_idx
)
# reorder incremental state in decoder
reorder_state = active_bbsz_idx
# sort by score descending
for sent in range(len(finalized)):
scores = torch.tensor(
[float(elem["score"].item()) for elem in finalized[sent]]
)
_, sorted_scores_indices = torch.sort(scores, descending=True)
finalized[sent] = [finalized[sent][ssi] for ssi in sorted_scores_indices]
finalized[sent] = torch.jit.annotate(
List[Dict[str, Tensor]], finalized[sent]
)
return finalized
def _prefix_tokens(
self, step: int, lprobs, scores, tokens, prefix_tokens, beam_size: int
):
"""Handle prefix tokens"""
prefix_toks = prefix_tokens[:, step].unsqueeze(-1).repeat(1, beam_size).view(-1)
prefix_lprobs = lprobs.gather(-1, prefix_toks.unsqueeze(-1))
prefix_mask = prefix_toks.ne(self.pad)
if self.constraint_trie is None:
lprobs[prefix_mask] = torch.min(prefix_lprobs) - 1
else:
lprobs[prefix_mask] = -math.inf
lprobs[prefix_mask] = lprobs[prefix_mask].scatter(
-1, prefix_toks[prefix_mask].unsqueeze(-1), prefix_lprobs[prefix_mask]
)
# if prefix includes eos, then we should make sure tokens and
# scores are the same across all beams
eos_mask = prefix_toks.eq(self.eos)
if eos_mask.any():
# validate that the first beam matches the prefix
first_beam = tokens[eos_mask].view(-1, beam_size, tokens.size(-1))[
:, 0, 1 : step + 1
]
eos_mask_batch_dim = eos_mask.view(-1, beam_size)[:, 0]
target_prefix = prefix_tokens[eos_mask_batch_dim][:, :step]
assert (first_beam == target_prefix).all()
# copy tokens, scores and lprobs from the first beam to all beams
tokens = self.replicate_first_beam(tokens, eos_mask_batch_dim, beam_size)
scores = self.replicate_first_beam(scores, eos_mask_batch_dim, beam_size)
lprobs = self.replicate_first_beam(lprobs, eos_mask_batch_dim, beam_size)
return lprobs, tokens, scores
def replicate_first_beam(self, tensor, mask, beam_size: int):
tensor = tensor.view(-1, beam_size, tensor.size(-1))
tensor[mask] = tensor[mask][:, :1, :]
return tensor.view(-1, tensor.size(-1))
def finalize_hypos(
self,
step: int,
bbsz_idx,
eos_scores,
tokens,
scores,
finalized: List[List[Dict[str, Tensor]]],
finished: List[bool],
beam_size: int,
attn: Optional[Tensor],
src_lengths,
max_len: int,
):
"""Finalize hypothesis, store finalized information in `finalized`, and change `finished` accordingly.
A sentence is finalized when {beam_size} finished items have been collected for it.
Returns number of sentences (not beam items) being finalized.
These will be removed from the batch and not processed further.
Args:
bbsz_idx (Tensor):
"""
assert bbsz_idx.numel() == eos_scores.numel()
# clone relevant token and attention tensors.
# tokens is (batch * beam, max_len). So the index_select
# gets the newly EOS rows, then selects cols 1..{step + 2}
tokens_clone = tokens.index_select(0, bbsz_idx)[
:, 1 : step + 2
] # skip the first index, which is EOS
tokens_clone[:, step] = self.eos
attn_clone = (
attn.index_select(0, bbsz_idx)[:, :, 1 : step + 2]
if attn is not None
else None
)
# compute scores per token position
pos_scores = scores.index_select(0, bbsz_idx)[:, : step + 1]
pos_scores[:, step] = eos_scores
# convert from cumulative to per-position scores
pos_scores[:, 1:] = pos_scores[:, 1:] - pos_scores[:, :-1]
# normalize sentence-level scores
if self.normalize_scores:
eos_scores /= (step + 1) ** self.len_penalty
# cum_unfin records which sentences in the batch are finished.
# It helps match indexing between (a) the original sentences
# in the batch and (b) the current, possibly-reduced set of
# sentences.
cum_unfin: List[int] = []
prev = 0
for f in finished:
if f:
prev += 1
else:
cum_unfin.append(prev)
cum_fin_tensor = torch.tensor(cum_unfin, dtype=torch.int).to(bbsz_idx)
unfin_idx = bbsz_idx // beam_size
sent = unfin_idx + torch.index_select(cum_fin_tensor, 0, unfin_idx)
# Create a set of "{sent}{unfin_idx}", where
# "unfin_idx" is the index in the current (possibly reduced)
# list of sentences, and "sent" is the index in the original,
# unreduced batch
# For every finished beam item
# sentence index in the current (possibly reduced) batch
seen = (sent << 32) + unfin_idx
unique_seen: List[int] = torch.unique(seen).tolist()
if self.match_source_len:
condition = step > torch.index_select(src_lengths, 0, unfin_idx)
eos_scores = torch.where(condition, torch.tensor(-math.inf), eos_scores)
sent_list: List[int] = sent.tolist()
for i in range(bbsz_idx.size()[0]):
# An input sentence (among those in a batch) is finished when
# beam_size hypotheses have been collected for it
if len(finalized[sent_list[i]]) < beam_size:
if attn_clone is not None:
# remove padding tokens from attn scores
hypo_attn = attn_clone[i]
else:
hypo_attn = torch.empty(0)
finalized[sent_list[i]].append(
{
"tokens": tokens_clone[i],
"score": eos_scores[i],
"attention": hypo_attn, # src_len x tgt_len
"alignment": torch.empty(0),
"positional_scores": pos_scores[i],
}
)
newly_finished: List[int] = []
for unique_s in unique_seen:
# check termination conditions for this sentence
unique_sent: int = unique_s >> 32
unique_unfin_idx: int = unique_s - (unique_sent << 32)
if not finished[unique_sent] and self.is_finished(
step, unique_unfin_idx, max_len, len(finalized[unique_sent]), beam_size
):
finished[unique_sent] = True
newly_finished.append(unique_unfin_idx)
return newly_finished
def is_finished(
self,
step: int,
unfin_idx: int,
max_len: int,
finalized_sent_len: int,
beam_size: int,
):
"""
Check whether decoding for a sentence is finished, which
occurs when the list of finalized sentences has reached the
beam size, or when we reach the maximum length.
"""
assert finalized_sent_len <= beam_size
if finalized_sent_len == beam_size or step == max_len:
return True
return False
class EnsembleModel(nn.Module):
"""A wrapper around an ensemble of models."""
def __init__(self, models):
super().__init__()
self.models_size = len(models)
# method '__len__' is not supported in ModuleList for torch script
self.single_model = models[0]
self.models = nn.ModuleList(models)
self.has_incremental: bool = False
if all(
hasattr(m, "decoder") and isinstance(m.decoder, FairseqIncrementalDecoder)
for m in models
):
self.has_incremental = True
def forward(self):
pass
def has_encoder(self):
return hasattr(self.single_model, "encoder")
def has_incremental_states(self):
return self.has_incremental
def max_decoder_positions(self):
return min([m.max_decoder_positions() for m in self.models if hasattr(m, "max_decoder_positions")] + [sys.maxsize])
@torch.jit.export
def forward_encoder(self, net_input: Dict[str, Tensor]):
if not self.has_encoder():
return None
return [model.encoder.forward_torchscript(net_input) for model in self.models]
@torch.jit.export
def forward_decoder(
self,
tokens,
encoder_outs: List[Dict[str, List[Tensor]]],
incremental_states: List[Dict[str, Dict[str, Optional[Tensor]]]],
temperature: float = 1.0,
constraint_trie=None,
constraint_start=None,
constraint_end=None,
gen_code=False,
zero_shot=False,
prefix_tokens=None
):
log_probs = []
avg_attn: Optional[Tensor] = None
encoder_out: Optional[Dict[str, List[Tensor]]] = None
code_mask = (tokens.new_ones(tokens.size(0))*gen_code).bool()
for i, model in enumerate(self.models):
if self.has_encoder():
encoder_out = encoder_outs[i]
# decode each model
if self.has_incremental_states():
decoder_out = model.decoder.forward(
tokens,
code_masks=code_mask,
encoder_out=encoder_out,
incremental_state=incremental_states[i],
)
else:
if hasattr(model, "decoder"):
decoder_out = model.decoder.forward(tokens, code_masks=code_mask, encoder_out=encoder_out)
else:
decoder_out = model.forward(tokens)
attn: Optional[Tensor] = None
decoder_len = len(decoder_out)
if decoder_len > 1 and decoder_out[1] is not None:
if isinstance(decoder_out[1], Tensor):
attn = decoder_out[1]
else:
attn_holder = decoder_out[1]["attn"]
if isinstance(attn_holder, Tensor):
attn = attn_holder
elif attn_holder is not None:
attn = attn_holder[0]
if attn is not None:
attn = attn[:, -1, :]
decoder_out_tuple = (
decoder_out[0][:, -1:, :].div_(temperature),
None if decoder_len <= 1 else decoder_out[1],
)
beam_size = decoder_out_tuple[0].size(0) // prefix_tokens.size(0) if prefix_tokens is not None else 0
if constraint_trie is not None and not zero_shot:
assert constraint_start is None and constraint_end is None
constraint_masks = decoder_out_tuple[0].new_zeros(decoder_out_tuple[0].size()).bool()
constraint_prefix_tokens = tokens.tolist()
for token_index, constraint_prefix_token in enumerate(constraint_prefix_tokens):
prefix_len = prefix_tokens[token_index // beam_size].ne(1).sum().item() if prefix_tokens is not None else 0
if len(constraint_prefix_token) > prefix_len:
constraint_prefix_token = [0] + constraint_prefix_token[prefix_len+1:]
constraint_nodes = constraint_trie.get_next_layer(constraint_prefix_token)
constraint_masks[token_index][:, constraint_nodes] = True
else:
constraint_masks[token_index] = True
decoder_out_tuple[0].masked_fill_(~constraint_masks, -math.inf)
if constraint_start is not None and constraint_end is not None and not zero_shot:
assert constraint_trie is None
decoder_out_tuple[0][:, :, 4:constraint_start] = -math.inf
decoder_out_tuple[0][:, :, constraint_end:] = -math.inf
probs = model.get_normalized_probs(
decoder_out_tuple, log_probs=True, sample=None
)
if constraint_trie is not None and zero_shot:
assert constraint_start is None and constraint_end is None
constraint_masks = decoder_out_tuple[0].new_zeros(decoder_out_tuple[0].size()).bool()
constraint_prefix_tokens = tokens.tolist()
for token_index, constraint_prefix_token in enumerate(constraint_prefix_tokens):
constraint_nodes = constraint_trie.get_next_layer(constraint_prefix_token)
constraint_masks[token_index][:, constraint_nodes] = True
probs.masked_fill_(~constraint_masks, -math.inf)
if constraint_start is not None and constraint_end is not None and zero_shot:
assert constraint_trie is None
probs[:, :, 4:constraint_start] = -math.inf
probs[:, :, constraint_end:] = -math.inf
probs = probs[:, -1, :]
if self.models_size == 1:
return probs, attn
log_probs.append(probs)
if attn is not None:
if avg_attn is None:
avg_attn = attn
else:
avg_attn.add_(attn)
avg_probs = torch.logsumexp(torch.stack(log_probs, dim=0), dim=0) - math.log(
self.models_size
)
if avg_attn is not None:
avg_attn.div_(self.models_size)
return avg_probs, avg_attn
@torch.jit.export
def reorder_encoder_out(
self, encoder_outs: Optional[List[Dict[str, List[Tensor]]]], new_order
):
"""
Reorder encoder output according to *new_order*.
Args:
encoder_out: output from the ``forward()`` method
new_order (LongTensor): desired order
Returns:
*encoder_out* rearranged according to *new_order*
"""
new_outs: List[Dict[str, List[Tensor]]] = []
if not self.has_encoder():
return new_outs
for i, model in enumerate(self.models):
assert encoder_outs is not None
new_outs.append(
model.encoder.reorder_encoder_out(encoder_outs[i], new_order)
)
return new_outs
@torch.jit.export
def reorder_incremental_state(
self,
incremental_states: List[Dict[str, Dict[str, Optional[Tensor]]]],
new_order,
):
if not self.has_incremental_states():
return
for i, model in enumerate(self.models):
model.decoder.reorder_incremental_state_scripting(
incremental_states[i], new_order
)
class SequenceGeneratorWithAlignment(SequenceGenerator):
def __init__(
self, models, tgt_dict, left_pad_target=False, print_alignment="hard", **kwargs
):
"""Generates translations of a given source sentence.
Produces alignments following "Jointly Learning to Align and
Translate with Transformer Models" (Garg et al., EMNLP 2019).
Args:
left_pad_target (bool, optional): Whether or not the
hypothesis should be left padded or not when they are
teacher forced for generating alignments.
"""
super().__init__(EnsembleModelWithAlignment(models), tgt_dict, **kwargs)
self.left_pad_target = left_pad_target
if print_alignment == "hard":
self.extract_alignment = utils.extract_hard_alignment
elif print_alignment == "soft":
self.extract_alignment = utils.extract_soft_alignment
@torch.no_grad()
def generate(self, models, sample, **kwargs):
finalized = super()._generate(sample, **kwargs)
src_tokens = sample["net_input"]["src_tokens"]
bsz = src_tokens.shape[0]
beam_size = self.beam_size
(
src_tokens,
src_lengths,
prev_output_tokens,
tgt_tokens,
) = self._prepare_batch_for_alignment(sample, finalized)
if any(getattr(m, "full_context_alignment", False) for m in self.model.models):
attn = self.model.forward_align(src_tokens, src_lengths, prev_output_tokens)
else:
attn = [
finalized[i // beam_size][i % beam_size]["attention"].transpose(1, 0)
for i in range(bsz * beam_size)
]
if src_tokens.device != "cpu":
src_tokens = src_tokens.to("cpu")
tgt_tokens = tgt_tokens.to("cpu")
attn = [i.to("cpu") for i in attn]
# Process the attn matrix to extract hard alignments.
for i in range(bsz * beam_size):
alignment = self.extract_alignment(
attn[i], src_tokens[i], tgt_tokens[i], self.pad, self.eos
)
finalized[i // beam_size][i % beam_size]["alignment"] = alignment
return finalized
def _prepare_batch_for_alignment(self, sample, hypothesis):
src_tokens = sample["net_input"]["src_tokens"]
bsz = src_tokens.shape[0]
src_tokens = (
src_tokens[:, None, :]
.expand(-1, self.beam_size, -1)
.contiguous()
.view(bsz * self.beam_size, -1)
)
src_lengths = sample["net_input"]["src_lengths"]
src_lengths = (
src_lengths[:, None]
.expand(-1, self.beam_size)
.contiguous()
.view(bsz * self.beam_size)
)
prev_output_tokens = data_utils.collate_tokens(
[beam["tokens"] for example in hypothesis for beam in example],
self.pad,
self.eos,
self.left_pad_target,
move_eos_to_beginning=True,
)
tgt_tokens = data_utils.collate_tokens(
[beam["tokens"] for example in hypothesis for beam in example],
self.pad,
self.eos,
self.left_pad_target,
move_eos_to_beginning=False,
)
return src_tokens, src_lengths, prev_output_tokens, tgt_tokens
class EnsembleModelWithAlignment(EnsembleModel):
"""A wrapper around an ensemble of models."""
def __init__(self, models):
super().__init__(models)
def forward_align(self, src_tokens, src_lengths, prev_output_tokens):
avg_attn = None
for model in self.models:
decoder_out = model(src_tokens, src_lengths, prev_output_tokens)
attn = decoder_out[1]["attn"][0]
if avg_attn is None:
avg_attn = attn
else:
avg_attn.add_(attn)
if len(self.models) > 1:
avg_attn.div_(len(self.models))
return avg_attn