diff --git a/ppdet/data/dataset.py b/ppdet/data/dataset.py
index 31d4df4a0146fd7bc5cdd21d02e06d58ebe0f99f..0ee38d12f06ee53cc99355e70d30184c3e2fd6b1 100644
--- a/ppdet/data/dataset.py
+++ b/ppdet/data/dataset.py
@@ -25,6 +25,7 @@ class Dataset(object):
 
     def __init__(self):
         self._epoch = -1
+        self._pos = 0
 
     def __next__(self):
         return self.next()
@@ -33,8 +34,8 @@ class Dataset(object):
         return self
 
     def __str__(self):
-        return "{}(fname:{}, epoch:{:d}, size:{:d}, pos:{:d})".format(
-            type(self).__name__, self._fname, self._epoch,
+        return "{}(epoch:{:d}, size:{:d}, pos:{:d})".format(
+            type(self).__name__, self._epoch,
             self.size(), self._pos)
 
     def next(self):
diff --git a/ppdet/data/source/roidb_source.py b/ppdet/data/source/roidb_source.py
index 4d898d95158d6e7747b13d459670b20598dea46b..44317974a1609e428e016467052f07cd2a7ceff3 100644
--- a/ppdet/data/source/roidb_source.py
+++ b/ppdet/data/source/roidb_source.py
@@ -82,8 +82,8 @@ class RoiDbSource(Dataset):
         self._imid2path = None
 
     def __str__(self):
-        return 'RoiDbSource(fname:%s,epoch:%d,size:%d,pos:%d)' \
-            % (self._fname, self._epoch, self.size(), self._pos)
+        return 'RoiDbSource(epoch:%d,size:%d,pos:%d,fname:%s)' \
+            % (self._epoch, self.size(), self._pos, self._fname)
 
     def next(self):
         """ load next sample
diff --git a/ppdet/data/tests/test_dataset.py b/ppdet/data/tests/test_dataset.py
new file mode 100644
index 0000000000000000000000000000000000000000..db99f464b7e897d52372896550ae8fe1adcb26c7
--- /dev/null
+++ b/ppdet/data/tests/test_dataset.py
@@ -0,0 +1,143 @@
+#   Copyright (c) 2019 PaddlePaddle Authors. All Rights Reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+import os
+import time
+import unittest
+import sys
+import logging
+import random
+import copy
+
+import set_env
+
+import ppdet.data.transform as tf
+from ppdet.data.dataset import Dataset
+
+class MemorySource(Dataset):
+    """ memory data source for testing
+    """
+    def __init__(self, samples):
+        super(MemorySource, self).__init__()
+        self._epoch = -1
+
+        self._pos = -1
+        self._drained = False
+        self._samples = samples
+
+    def next(self):
+        if self._epoch < 0:
+            self.reset()
+
+        if self._pos >= self.size():
+            self._drained = True
+            raise StopIteration("no more data in " + str(self))
+        else:
+            sample = copy.deepcopy(self._samples[self._pos])
+            self._pos += 1
+            return sample
+
+    def reset(self):
+        if self._epoch < 0:
+            self._epoch = 0
+        else:
+            self._epoch += 1
+
+        self._pos = 0
+        self._drained = False
+        random.shuffle(self._samples)
+
+    def size(self):
+        return len(self._samples)
+
+    def drained(self):
+        assert self._epoch >= 0, "the first epoch has not started yet"
+        return self._pos >= self.size()
+
+    def epoch_id(self):
+        return self._epoch
+
+
+class TestDataset(unittest.TestCase):
+    """Test cases for ppdet.data.dataset
+    """
+
+    @classmethod
+    def setUpClass(cls):
+        """ setup
+        """
+        pass
+
+    @classmethod
+    def tearDownClass(cls):
+        """ tearDownClass """
+        pass
+
+    def test_next(self):
+        """ test next
+        """
+        samples = list(range(10))
+        mem_sc = MemorySource(samples)
+
+        for i, d in enumerate(mem_sc):
+            self.assertTrue(d in samples)
+
+    def test_transform_with_abnormal_worker(self):
+        """ test dataset transform with abnormally exit process
+        """
+        samples = list(range(1000))
+        ds = MemorySource(samples)
+
+        def _mapper(sample):
+            if sample == 3:
+                sys.exit(1)
+
+            return 2 * sample
+
+        worker_conf = {'WORKER_NUM': 2, 'use_process': True}
+        mapped = tf.map(ds, _mapper, worker_conf)
+
+        ct = 0
+        for i, d in enumerate(mapped):
+            ct += 1
+            self.assertTrue(d / 2 in samples)
+
+        self.assertEqual(len(samples) - 1, ct)
+
+    def test_transform_with_delay_worker(self):
+        """ test dataset transform with delayed process
+        """
+        samples = list(range(1000))
+        ds = MemorySource(samples)
+
+        def _mapper(sample):
+            if sample == 3:
+                time.sleep(30)
+
+            return 2 * sample
+
+        worker_conf = {'WORKER_NUM': 2, 'use_process': True}
+        mapped = tf.map(ds, _mapper, worker_conf)
+
+        ct = 0
+        for i, d in enumerate(mapped):
+            ct += 1
+            self.assertTrue(d / 2 in samples)
+
+        self.assertEqual(len(samples), ct)
+
+
+if __name__ == '__main__':
+    logging.basicConfig()
+    unittest.main()
+
diff --git a/ppdet/data/transform/parallel_map.py b/ppdet/data/transform/parallel_map.py
index a4dfa05565bdf4d84bc96704688f154256bf2678..bb4ff6e48d5887d69acc723b9eb12cba0b747a4d 100644
--- a/ppdet/data/transform/parallel_map.py
+++ b/ppdet/data/transform/parallel_map.py
@@ -21,6 +21,11 @@ from __future__ import print_function
 
 import sys
 import six
+if six.PY3:
+    from queue import Empty
+else:
+    from Queue import Empty
+
 import uuid
 import logging
 import signal
@@ -31,15 +36,19 @@ logger = logging.getLogger(__name__)
 
 
 class EndSignal(object):
-    def __init__(self, errno=0, errmsg=''):
+    """ signal used to notify worker to exit
+    """
+    def __init__(self, id, errno=0, errmsg=''):
+        self.id = id
         self.errno = errno
         self.errmsg = errmsg
 
 
 class ParallelMappedDataset(ProxiedDataset):
     """
-    Transform samples to mapped samples which is similar to 'basic.MappedDataset',
-    but multiple workers (threads or processes) will be used
+    Transform samples to mapped samples which is similar to 
+    'basic.MappedDataset', but multiple workers (threads or processes) 
+    will be used
 
     Notes:
         this class is not thread-safe
@@ -58,9 +67,10 @@ class ParallelMappedDataset(ProxiedDataset):
         args.update(worker_args)
         if args['use_process'] and type(args['memsize']) is str:
             assert args['memsize'][-1].lower() == 'g', \
-                "invalid param for memsize[%s], should be ended with 'G' or 'g'" % (args['memsize'])
+                "invalid param for memsize[{}], should " \
+                "be ended with 'G' or 'g'".format(args['memsize'])
             gb = args['memsize'][:-1]
-            args['memsize'] = int(gb) * 1024**3
+            args['memsize'] = int(gb) * 1024 ** 3
 
         self._worker_args = args
         self._started = False
@@ -103,22 +113,25 @@ class ParallelMappedDataset(ProxiedDataset):
         self._producer.daemon = True
 
         self._consumers = []
+        self._consumer_endsig = {}
         for i in range(consumer_num):
+            consumer_id = 'consumer-' + id + '-' + str(i)
             p = Worker(
                 target=self._consume,
-                args=('consumer-' + id + '_' + str(i), self._inq, self._outq,
+                args=(consumer_id, self._inq, self._outq,
                       self._mapper))
             self._consumers.append(p)
             p.daemon = True
+            setattr(p, 'id', consumer_id)
 
         self._epoch = -1
         self._feeding_ev = Event()
         self._produced = 0  # produced sample in self._produce
         self._consumed = 0  # consumed sample in self.next
-        self._stopped_consumers = 0
 
     def _produce(self, id, source, inq):
         """Fetch data from source and feed it to 'inq' queue"""
+        endsig = EndSignal(id)
         while True:
             self._feeding_ev.wait()
             if self._exit:
@@ -128,32 +141,38 @@ class ParallelMappedDataset(ProxiedDataset):
                 self._produced += 1
             except StopIteration:
                 self._feeding_ev.clear()
-                self._feeding_ev.wait()  # wait other guy to wake up me
-                logger.debug("producer[{}] starts new epoch".format(id))
+                self._feeding_ev.wait()
             except Exception as e:
-                msg = "producer[{}] failed with error: {}".format(id, str(e))
-                inq.put(EndSignal(-1, msg))
+                endsig.errno = -1
+                endsig.errmsg = "producer[{}] failed with error: {}" \
+                    .format(id, str(e))
+                inq.put(endsig)
                 break
 
-        logger.debug("producer[{}] exits".format(id))
-
     def _consume(self, id, inq, outq, mapper):
         """Fetch data from 'inq', process it and put result to 'outq'"""
+        if self._worker_args['use_process']:
+            # handle SIGTERM signal to exit to prevent print stack frame
+            signal.signal(signal.SIGTERM, lambda signum, frame : sys.exit())
+
+        endsig = EndSignal(id)
         while True:
             sample = inq.get()
             if isinstance(sample, EndSignal):
-                sample.errmsg += "[consumer[{}] exits]".format(id)
-                outq.put(sample)
-                logger.debug("end signal received, " +
-                             "consumer[{}] exits".format(id))
+                endsig.errno = sample.errno
+                endsig.errmsg = "consumer[{}] exits for reason[{}]" \
+                    .format(id, sample.errmsg)
+                outq.put(endsig)
                 break
 
             try:
                 result = mapper(sample)
                 outq.put(result)
             except Exception as e:
-                msg = 'failed to map consumer[%s], error: {}'.format(str(e), id)
-                outq.put(EndSignal(-1, msg))
+                endsig.errno = -2
+                endsig.errmsg = "consumer[{}] failed to map with error:[{}]" \
+                    .format(id, str(e))
+                outq.put(endsig)
                 break
 
     def drained(self):
@@ -168,6 +187,25 @@ class ParallelMappedDataset(ProxiedDataset):
         for _ in range(len(self._consumers)):
             self._inq.put(EndSignal(0, "notify consumers to exit"))
 
+    def _consumer_healthy(self):
+        abnormal_num = 0
+        for w in self._consumers:
+            if not w.is_alive() and w.id not in self._consumer_endsig:
+                abnormal_num += 1
+                if self._worker_args['use_process']:
+                    errmsg = "consumer[{}] exit abnormally with exitcode[{}]" \
+                                .format(w.pid, w.exitcode)
+                else:
+                    errmsg = "consumer[{}] exit abnormally".format(w.ident)
+    
+                logger.warn(errmsg)
+
+        if abnormal_num > 0:
+            logger.warn("{} consumers have exited abnormally!!!" \
+                .format(abnormal_num))
+
+        return abnormal_num == 0
+
     def next(self):
         """ get next transformed sample
         """
@@ -177,41 +215,54 @@ class ParallelMappedDataset(ProxiedDataset):
         if self.drained():
             raise StopIteration()
 
-        while True:
-            sample = self._outq.get()
+        while not self._exit:
+            try:
+                sample = self._outq.get(timeout=3)
+            except Empty as e:
+                if not self._consumer_healthy():
+                    raise StopIteration()
+                else:
+                    continue
+
             if isinstance(sample, EndSignal):
-                self._stopped_consumers += 1
-                if sample.errno != 0:
-                    logger.warn("consumer failed with error: {}".format(
-                        sample.errmsg))
+                self._consumer_endsig[sample.id] = sample
+                logger.warn("recv endsignal from outq with errmsg[{}]" \
+                    .format(sample.errmsg))
 
-                if self._stopped_consumers < len(self._consumers):
+                if len(self._consumer_endsig.keys()) < len(self._consumers):
                     self._inq.put(sample)
                 else:
-                    raise ValueError("all consumers exited, no more samples")
+                    self._exit = True
+                    raise StopIteration("all consumers exited, no more samples")
             else:
                 self._consumed += 1
                 return sample
 
+        raise StopIteration()
+
     def reset(self):
         """ reset for a new epoch of samples
         """
+        assert not self._exit, "cannot reset for already stopped dataset"
+
         if self._epoch < 0:
             self._epoch = 0
-            for p in self._consumers:
-                p.start()
+            for w in self._consumers:
+                w.start()
             self._producer.start()
         else:
+            assert self._consumer_healthy(), "cannot start another pass of data" \
+                " for some consumers exited abnormally before!!!"
+
             if not self.drained():
-                logger.warn("do not reset before epoch[%d] finishes".format(
-                    self._epoch))
+                logger.warn("reset before epoch[{}] finishes".format(self._epoch))
                 self._produced = self._produced - self._consumed
             else:
                 self._produced = 0
 
             self._epoch += 1
 
-        assert self._stopped_consumers == 0, "some consumers already exited," \
+        assert len(self._consumer_endsig.keys()) == 0, "some consumers already exited," \
             + " cannot start another epoch"
 
         self._source.reset()
@@ -221,9 +272,4 @@ class ParallelMappedDataset(ProxiedDataset):
 
 # FIXME(dengkaipeng): fix me if you have better impliment
 # handle terminate reader process, do not print stack frame
-def _reader_exit(signum, frame):
-    logger.debug("Reader process exit.")
-    sys.exit()
-
-
-signal.signal(signal.SIGTERM, _reader_exit)
+signal.signal(signal.SIGTERM, lambda signum, frame : sys.exit())
diff --git a/ppdet/data/transform/shared_queue/queue.py b/ppdet/data/transform/shared_queue/queue.py
index 0bd44d3e9e0b34cefa3adfd8008a90e0963c5b62..8f0ba8ab462114f41333fdc3720ef013ceb56c85 100644
--- a/ppdet/data/transform/shared_queue/queue.py
+++ b/ppdet/data/transform/shared_queue/queue.py
@@ -22,9 +22,11 @@ import six
 if six.PY3:
     import pickle
     from io import BytesIO as StringIO
+    from queue import Empty
 else:
     import cPickle as pickle
     from cStringIO import StringIO
+    from Queue import Empty
 
 import logging
 import traceback
@@ -87,6 +89,8 @@ class SharedQueue(Queue):
             buff = super(SharedQueue, self).get(**kwargs)
             data = buff.get()
             return pickle.load(StringIO(data))
+        except Empty as e:
+            raise e
         except Exception as e:
             stack_info = traceback.format_exc()
             err_msg = 'failed to get element from SharedQueue '\
diff --git a/ppdet/data/transform/shared_queue/sharedmemory.py b/ppdet/data/transform/shared_queue/sharedmemory.py
index 933ab24c211cf97f477dfb1437fcf6c7cab9392f..8b1d3ab40f919d2fb72286b6b6e282881fc8193c 100644
--- a/ppdet/data/transform/shared_queue/sharedmemory.py
+++ b/ppdet/data/transform/shared_queue/sharedmemory.py
@@ -316,8 +316,6 @@ class PageAllocator(object):
         start_pos = pos
         flags = ''
         while True:
-            # maybe flags already has some '0' pages,
-            # so just check 'page_num - len(flags)' pages
             flags = self.get_page_status(pos, page_num, ret_flag=True)
 
             if flags.count('0') == page_num:
@@ -343,10 +341,10 @@ class PageAllocator(object):
             if free_pages == 0:
                 err_msg = 'all pages have been used:%s' % (str(self))
             else:
-                err_msg = 'not found available pages with page_status[%s] '\
-                    'and %d free pages' % (str(page_status), free_pages)
-            err_msg = 'failed to malloc %d pages at pos[%d] for reason[%s] and allocator status[%s]' \
-                % (page_num, pos, err_msg, str(self))
+                err_msg = 'not found enough pages[avail:%d, expect:%d] '\
+                    'with total free pages[%d]' % (page_status[0], page_num, free_pages)
+            err_msg = 'failed to malloc %d pages at pos[%d] for reason[%s] '\
+                    'and allocator status[%s]' % (page_num, pos, err_msg, str(self))
             raise MemoryFullError(err_msg)
 
         self.set_page_status(pos, page_num, '1')