# Copyright (c) Open-MMLab. All rights reserved.
import os.path as osp
import time

import torch
from torch.optim import Optimizer

import mmcv
from .base_runner import BaseRunner
from .checkpoint import save_checkpoint
from .hooks import IterTimerHook
from .utils import get_host_info


class IterLoader:

    def __init__(self, dataloader):
        self._dataloader = dataloader
        self.iter_loader = iter(self._dataloader)
        self._epoch = 0

    @property
    def epoch(self):
        return self._epoch

    def __next__(self):
        try:
            data = next(self.iter_loader)
        except StopIteration:
            self._epoch += 1
            if hasattr(self._dataloader.sampler, 'set_epoch'):
                self._dataloader.sampler.set_epoch(self._epoch)
            self.iter_loader = iter(self._dataloader)
            data = next(self.iter_loader)

        return data

    def __len__(self):
        return len(self._dataloader)


class IterBasedRunner(BaseRunner):
    """Iteration-based Runner.

    This runner train models iteration by iteration.
    """

    def train(self, data_loader, **kwargs):
        self.model.train()
        self.mode = 'train'
        self.data_loader = data_loader
        self._epoch = data_loader.epoch
        self.call_hook('before_train_iter')
        data_batch = next(data_loader)
        outputs = self.model.train_step(data_batch, self.optimizer, **kwargs)
        if not isinstance(outputs, dict):
            raise TypeError('model.train_step() must return a dict')
        if 'log_vars' in outputs:
            self.log_buffer.update(outputs['log_vars'], outputs['num_samples'])
        self.outputs = outputs
        self.call_hook('after_train_iter')
        self._inner_iter += 1
        self._iter += 1

    def val(self, data_loader, **kwargs):
        self.model.eval()
        self.mode = 'val'
        self.data_loader = data_loader
        self.call_hook('before_val_iter')
        data_batch = next(data_loader)
        outputs = self.model.val_step(data_batch, **kwargs)
        if not isinstance(outputs, dict):
            raise TypeError('model.val_step() must return a dict')
        if 'log_vars' in outputs:
            self.log_buffer.update(outputs['log_vars'], outputs['num_samples'])
        self.outputs = outputs
        self.call_hook('after_val_iter')
        self._inner_iter += 1

    def run(self, data_loaders, workflow, max_iters, **kwargs):
        """Start running.

        Args:
            data_loaders (list[:obj:`DataLoader`]): Dataloaders for training
                and validation.
            workflow (list[tuple]): A list of (phase, iters) to specify the
                running order and iterations. E.g, [('train', 10000),
                ('val', 1000)] means running 10000 iterations for training and
                1000 iterations for validation, iteratively.
            max_iters (int): Total training iterations.
        """
        assert isinstance(data_loaders, list)
        assert mmcv.is_list_of(workflow, tuple)
        assert len(data_loaders) == len(workflow)

        self._max_iters = max_iters
        work_dir = self.work_dir if self.work_dir is not None else 'NONE'
        self.logger.info('Start running, host: %s, work_dir: %s',
                         get_host_info(), work_dir)
        self.logger.info('workflow: %s, max: %d iters', workflow, max_iters)
        self.call_hook('before_run')

        iter_loaders = [IterLoader(x) for x in data_loaders]

        self.call_hook('before_epoch')

        while self.iter < max_iters:
            for i, flow in enumerate(workflow):
                self._inner_iter = 0
                mode, iters = flow
                if not isinstance(mode, str) or not hasattr(self, mode):
                    raise ValueError(
                        'runner has no method named "{}" to run a workflow'.
                        format(mode))
                iter_runner = getattr(self, mode)
                for _ in range(iters):
                    if mode == 'train' and self.iter >= max_iters:
                        break
                    iter_runner(iter_loaders[i], **kwargs)

        time.sleep(1)  # wait for some hooks like loggers to finish
        self.call_hook('after_epoch')
        self.call_hook('after_run')

    def resume(self,
               checkpoint,
               resume_optimizer=True,
               map_location='default'):
        """Resume model from checkpoint.

        Args:
            checkpoint (str): Checkpoint to resume from.
            resume_optimizer (bool, optional): Whether resume the optimizer(s)
                if the checkpoint file includes optimizer(s). Default to True.
            map_location (str, optional): Same as :func:`torch.load`.
                Default to 'default'.
        """
        if map_location == 'default':
            device_id = torch.cuda.current_device()
            checkpoint = self.load_checkpoint(
                checkpoint,
                map_location=lambda storage, loc: storage.cuda(device_id))
        else:
            checkpoint = self.load_checkpoint(
                checkpoint, map_location=map_location)

        self._epoch = checkpoint['meta']['epoch']
        self._iter = checkpoint['meta']['iter']
        self._inner_iter = checkpoint['meta']['iter']
        if 'optimizer' in checkpoint and resume_optimizer:
            if isinstance(self.optimizer, Optimizer):
                self.optimizer.load_state_dict(checkpoint['optimizer'])
            elif isinstance(self.optimizer, dict):
                for k in self.optimizer.keys():
                    self.optimizer[k].load_state_dict(
                        checkpoint['optimizer'][k])

        self.logger.info(f'resumed from epoch: {self.epoch}, iter {self.iter}')

    def save_checkpoint(self,
                        out_dir,
                        filename_tmpl='iter_{}.pth',
                        meta=None,
                        save_optimizer=True,
                        create_symlink=True):
        """Save checkpoint to file.

        Args:
            out_dir (str): Directory to save checkpoint files.
            filename_tmpl (str, optional): Checkpoint file template.
                Defaults to 'iter_{}.pth'.
            meta (dict, optional): Metadata to be saved in checkpoint.
                Defaults to None.
            save_optimizer (bool, optional): Whether save optimizer.
                Defaults to True.
            create_symlink (bool, optional): Whether create symlink to the
                latest checkpoint file. Defaults to True.
        """
        if meta is None:
            meta = dict(iter=self.iter + 1, epoch=self.epoch + 1)
        elif isinstance(meta, dict):
            meta.update(iter=self.iter + 1, epoch=self.epoch + 1)
        else:
            raise TypeError(
                f'meta should be a dict or None, but got {type(meta)}')
        if self.meta is not None:
            meta.update(self.meta)

        filename = filename_tmpl.format(self.iter + 1)
        filepath = osp.join(out_dir, filename)
        optimizer = self.optimizer if save_optimizer else None
        save_checkpoint(self.model, filepath, optimizer=optimizer, meta=meta)
        # in some environments, `os.symlink` is not supported, you may need to
        # set `create_symlink` to False
        if create_symlink:
            mmcv.symlink(filename, osp.join(out_dir, 'latest.pth'))

    def register_training_hooks(self,
                                lr_config,
                                optimizer_config=None,
                                checkpoint_config=None,
                                log_config=None,
                                momentum_config=None):
        """Register default hooks for iter-based training.

        Default hooks include:

        - LrUpdaterHook
        - MomentumUpdaterHook
        - OptimizerStepperHook
        - CheckpointSaverHook
        - IterTimerHook
        - LoggerHook(s)
        """
        if checkpoint_config is not None:
            checkpoint_config.setdefault('by_epoch', False)
        if lr_config is not None:
            lr_config.setdefault('by_epoch', False)
        self.register_lr_hook(lr_config)
        self.register_momentum_hook(momentum_config)
        self.register_optimizer_hook(optimizer_config)
        self.register_checkpoint_hook(checkpoint_config)
        self.register_hook(IterTimerHook())
        if log_config is not None:
            log_config.setdefault('by_epoch', False)
        self.register_logger_hooks(log_config)

mmcv/runner/iter_based_runner.py
# Copyright (c) Open-MMLab. All rights reserved.
import os.path as osp
import time

import torch
from torch.optim import Optimizer

import mmcv
from .base_runner import BaseRunner
from .checkpoint import save_checkpoint
from .hooks import IterTimerHook
from .utils import get_host_info


class IterLoader:

    def __init__(self, dataloader):
        self._dataloader = dataloader
        self.iter_loader = iter(self._dataloader)
        self._epoch = 0

    @property
    def epoch(self):
        return self._epoch

    def __next__(self):
        try:
            data = next(self.iter_loader)
        except StopIteration:
            self._epoch += 1
            if hasattr(self._dataloader.sampler, 'set_epoch'):
                self._dataloader.sampler.set_epoch(self._epoch)
            self.iter_loader = iter(self._dataloader)
            data = next(self.iter_loader)

        return data

    def __len__(self):
        return len(self._dataloader)


class IterBasedRunner(BaseRunner):
    """Iteration-based Runner.

    This runner train models iteration by iteration.
    """

    def train(self, data_loader, **kwargs):
        self.model.train()
        self.mode = 'train'
        self.data_loader = data_loader
        self._epoch = data_loader.epoch
        self.call_hook('before_train_iter')
        data_batch = next(data_loader)
        outputs = self.model.train_step(data_batch, self.optimizer, **kwargs)
        if not isinstance(outputs, dict):
            raise TypeError('model.train_step() must return a dict')
        if 'log_vars' in outputs:
            self.log_buffer.update(outputs['log_vars'], outputs['num_samples'])
        self.outputs = outputs
        self.call_hook('after_train_iter')
        self._inner_iter += 1
        self._iter += 1

    def val(self, data_loader, **kwargs):
        self.model.eval()
        self.mode = 'val'
        self.data_loader = data_loader
        self.call_hook('before_val_iter')
        data_batch = next(data_loader)
        outputs = self.model.val_step(data_batch, **kwargs)
        if not isinstance(outputs, dict):
            raise TypeError('model.val_step() must return a dict')
        if 'log_vars' in outputs:
            self.log_buffer.update(outputs['log_vars'], outputs['num_samples'])
        self.outputs = outputs
        self.call_hook('after_val_iter')
        self._inner_iter += 1

    def run(self, data_loaders, workflow, max_iters, **kwargs):
        """Start running.

        Args:
            data_loaders (list[:obj:`DataLoader`]): Dataloaders for training
                and validation.
            workflow (list[tuple]): A list of (phase, iters) to specify the
                running order and iterations. E.g, [('train', 10000),
                ('val', 1000)] means running 10000 iterations for training and
                1000 iterations for validation, iteratively.
            max_iters (int): Total training iterations.
        """
        assert isinstance(data_loaders, list)
        assert mmcv.is_list_of(workflow, tuple)
        assert len(data_loaders) == len(workflow)

        self._max_iters = max_iters
        work_dir = self.work_dir if self.work_dir is not None else 'NONE'
        self.logger.info('Start running, host: %s, work_dir: %s',
                         get_host_info(), work_dir)
        self.logger.info('workflow: %s, max: %d iters', workflow, max_iters)
        self.call_hook('before_run')

        iter_loaders = [IterLoader(x) for x in data_loaders]

        self.call_hook('before_epoch')

        while self.iter < max_iters:
            for i, flow in enumerate(workflow):
                self._inner_iter = 0
                mode, iters = flow
                if not isinstance(mode, str) or not hasattr(self, mode):
                    raise ValueError(
                        'runner has no method named "{}" to run a workflow'.
                        format(mode))
                iter_runner = getattr(self, mode)
                for _ in range(iters):
                    if mode == 'train' and self.iter >= max_iters:
                        break
                    iter_runner(iter_loaders[i], **kwargs)

        time.sleep(1)  # wait for some hooks like loggers to finish
        self.call_hook('after_epoch')
        self.call_hook('after_run')

    def resume(self,
               checkpoint,
               resume_optimizer=True,
               map_location='default'):
        """Resume model from checkpoint.

        Args:
            checkpoint (str): Checkpoint to resume from.
            resume_optimizer (bool, optional): Whether resume the optimizer(s)
                if the checkpoint file includes optimizer(s). Default to True.
            map_location (str, optional): Same as :func:`torch.load`.
                Default to 'default'.
        """
        if map_location == 'default':
            device_id = torch.cuda.current_device()
            checkpoint = self.load_checkpoint(
                checkpoint,
                map_location=lambda storage, loc: storage.cuda(device_id))
        else:
            checkpoint = self.load_checkpoint(
                checkpoint, map_location=map_location)

        self._epoch = checkpoint['meta']['epoch']
        self._iter = checkpoint['meta']['iter']
        self._inner_iter = checkpoint['meta']['iter']
        if 'optimizer' in checkpoint and resume_optimizer:
            if isinstance(self.optimizer, Optimizer):
                self.optimizer.load_state_dict(checkpoint['optimizer'])
            elif isinstance(self.optimizer, dict):
                for k in self.optimizer.keys():
                    self.optimizer[k].load_state_dict(
                        checkpoint['optimizer'][k])

        self.logger.info(f'resumed from epoch: {self.epoch}, iter {self.iter}')

    def save_checkpoint(self,
                        out_dir,
                        filename_tmpl='iter_{}.pth',
                        meta=None,
                        save_optimizer=True,
                        create_symlink=True):
        """Save checkpoint to file.

        Args:
            out_dir (str): Directory to save checkpoint files.
            filename_tmpl (str, optional): Checkpoint file template.
                Defaults to 'iter_{}.pth'.
            meta (dict, optional): Metadata to be saved in checkpoint.
                Defaults to None.
            save_optimizer (bool, optional): Whether save optimizer.
                Defaults to True.
            create_symlink (bool, optional): Whether create symlink to the
                latest checkpoint file. Defaults to True.
        """
        if meta is None:
            meta = dict(iter=self.iter + 1, epoch=self.epoch + 1)
        elif isinstance(meta, dict):
            meta.update(iter=self.iter + 1, epoch=self.epoch + 1)
        else:
            raise TypeError(
                f'meta should be a dict or None, but got {type(meta)}')
        if self.meta is not None:
            meta.update(self.meta)

        filename = filename_tmpl.format(self.iter + 1)
        filepath = osp.join(out_dir, filename)
        optimizer = self.optimizer if save_optimizer else None
        save_checkpoint(self.model, filepath, optimizer=optimizer, meta=meta)
        # in some environments, `os.symlink` is not supported, you may need to
        # set `create_symlink` to False
        if create_symlink:
            mmcv.symlink(filename, osp.join(out_dir, 'latest.pth'))

    def register_training_hooks(self,
                                lr_config,
                                optimizer_config=None,
                                checkpoint_config=None,
                                log_config=None,
                                momentum_config=None):
        """Register default hooks for iter-based training.

        Default hooks include:

        - LrUpdaterHook
        - MomentumUpdaterHook
        - OptimizerStepperHook
        - CheckpointSaverHook
        - IterTimerHook
        - LoggerHook(s)
        """
        if checkpoint_config is not None:
            checkpoint_config.setdefault('by_epoch', False)
        if lr_config is not None:
            lr_config.setdefault('by_epoch', False)
        self.register_lr_hook(lr_config)
        self.register_momentum_hook(momentum_config)
        self.register_optimizer_hook(optimizer_config)
        self.register_checkpoint_hook(checkpoint_config)
        self.register_hook(IterTimerHook())
        if log_config is not None:
            for info in log_config['hooks']:
                info.setdefault('by_epoch', False)
        self.register_logger_hooks(log_config)

mmcv/runner/iter_based_runner.py
diff --git a/mmcv/runner/iter_based_runner.py b/mmcv/runner/iter_based_runner.py
index 3a3d22f2fc..f41a86a9d4 100644
--- a/mmcv/runner/iter_based_runner.py
+++ b/mmcv/runner/iter_based_runner.py
@@ -222,5 +222,6 @@ def register_training_hooks(self,
         self.register_checkpoint_hook(checkpoint_config)
         self.register_hook(IterTimerHook())
         if log_config is not None:
-            log_config.setdefault('by_epoch', False)
+            for info in log_config['hooks']:
+                info.setdefault('by_epoch', False)
         self.register_logger_hooks(log_config)

Bug feedback.
Thanks for your codes. 
In [mmcv/runner/base_runner](https://github.com/open-mmlab/mmcv/blob/master/mmcv/runner/base_runner.py#L385), 
`    def register_logger_hooks(self, log_config):
        log_interval = log_config['interval']
        for info in log_config['hooks']:
            logger_hook = mmcv.build_from_cfg(
                info, HOOKS, default_args=dict(interval=log_interval))
            self.register_hook(logger_hook, priority='VERY_LOW')
`
.
Only the argument 'interval' in log_config is fed into logger_hook. However, the argument 'by_epoch' is ignored, always true, so that if iter_based_runner is used, the logger will work unexpectedly. 
