PERF: Released the GIL from parts of the TextReader class

The GIL was released around the tokenizer functions and the conversion function(_string_convert excluded).

Author: Jean-Mathieu Deschenes

asv_bench/benchmarks/gil.py

@@ -1,15 +1,24 @@
 from .pandas_vb_common import *
 from pandas.core import common as com
+
+try:
+    from cStringIO import StringIO
+except ImportError:
+    from io import StringIO
+
 try:
     from pandas.util.testing import test_parallel
+
     have_real_test_parallel = True
 except ImportError:
     have_real_test_parallel = False
 
+
     def test_parallel(num_threads=1):
 
         def wrapper(fname):
             return fname
+
         return wrapper
 
 
@@ -321,6 +330,7 @@ def run(arr):
             algos.kth_smallest(arr, self.k)
         run()
 
+
 class nogil_datetime_fields(object):
     goal_time = 0.2
 
@@ -435,4 +445,47 @@ def time_nogil_rolling_std(self):
         @test_parallel(num_threads=2)
         def run(arr, win):
             rolling_std(arr, win)
-        run(self.arr, self.win)
+        run(self.arr, self.win)
+
+
+class nogil_read_csv(object):
+    number = 1
+    repeat = 5
+
+    def setup(self):
+        if (not have_real_test_parallel):
+            raise NotImplementedError
+        # Using the values
+        self.df = DataFrame(np.random.randn(10000, 50))
+        self.df.to_csv('__test__.csv')
+
+        self.rng = date_range('1/1/2000', periods=10000)
+        self.df_date_time = DataFrame(np.random.randn(10000, 50), index=self.rng)
+        self.df_date_time.to_csv('__test_datetime__.csv')
+
+        self.df_object = DataFrame('foo', index=self.df.index, columns=self.create_cols('object'))
+        self.df_object.to_csv('__test_object__.csv')
+
+    def create_cols(self, name):
+        return [('%s%03d' % (name, i)) for i in range(5)]
+
+    @test_parallel(num_threads=2)
+    def pg_read_csv(self):
+        read_csv('__test__.csv', sep=',', header=None, float_precision=None)
+
+    def time_nogil_read_csv(self):
+        self.pg_read_csv()
+
+    @test_parallel(num_threads=2)
+    def pg_read_csv_object(self):
+        read_csv('__test_object__.csv', sep=',')
+
+    def time_nogil_read_csv_object(self):
+        self.pg_read_csv_object()
+
+    @test_parallel(num_threads=2)
+    def pg_read_csv_datetime(self):
+        read_csv('__test_datetime__.csv', sep=',', header=None)
+
+    def time_nogil_read_csv_datetime(self):
+        self.pg_read_csv_datetime()

doc/source/whatsnew/v0.17.1.txt

@@ -60,6 +60,7 @@ Performance Improvements
 
 - Release the GIL on most datetime field operations (e.g. ``DatetimeIndex.year``, ``Series.dt.year``), normalization, and conversion to and from ``Period``, ``DatetimeIndex.to_period`` and ``PeriodIndex.to_timestamp`` (:issue:`11263`)
 - Release the GIL on some srolling algos (``rolling_median``, ``rolling_mean``, ``rolling_max``, ``rolling_min``, ``rolling_var``, ``rolling_kurt``, `rolling_skew`` (:issue:`11450`)
+- Release the GIL when reading and parsing text files in ``read_csv``, ``read_table`` (:issue:`11272`)
 - Improved performance of ``rolling_median`` (:issue:`11450`)
 
 - Improved performance to ``to_excel`` (:issue:`11352`)