From c52c7f4bfb1133456b225e25a4ada94ad25e1e91 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Johannes=20Sch=C3=B6nberger?= <jsch@demuc.de>
Date: Wed, 20 May 2015 07:38:47 -0700
Subject: [PATCH] Do not acquire GIL for ORB

---
 skimage/feature/orb_cy.pyx        | 35 ++++++++++++++++---------------
 skimage/feature/tests/test_orb.py |  2 ++
 2 files changed, 20 insertions(+), 17 deletions(-)

diff --git a/skimage/feature/orb_cy.pyx b/skimage/feature/orb_cy.pyx
index 49c4e650..b3140aa5 100644
--- a/skimage/feature/orb_cy.pyx
+++ b/skimage/feature/orb_cy.pyx
@@ -30,27 +30,28 @@ def _orb_loop(double[:, ::1] image, Py_ssize_t[:, ::1] keypoints,
     cdef signed char[:, ::1] cpos0 = POS0
     cdef signed char[:, ::1] cpos1 = POS1
 
-    for i in range(descriptors.shape[0]):
+    with nogil:
+        for i in range(descriptors.shape[0]):
 
-        angle = orientations[i]
-        sin_a = sin(angle)
-        cos_a = cos(angle)
+            angle = orientations[i]
+            sin_a = sin(angle)
+            cos_a = cos(angle)
 
-        kr = keypoints[i, 0]
-        kc = keypoints[i, 1]
+            kr = keypoints[i, 0]
+            kc = keypoints[i, 1]
 
-        for j in range(descriptors.shape[1]):
-            pr0 = cpos0[j, 0]
-            pc0 = cpos0[j, 1]
-            pr1 = cpos1[j, 0]
-            pc1 = cpos1[j, 1]
+            for j in range(descriptors.shape[1]):
+                pr0 = cpos0[j, 0]
+                pc0 = cpos0[j, 1]
+                pr1 = cpos1[j, 0]
+                pc1 = cpos1[j, 1]
 
-            spr0 = <Py_ssize_t>round(sin_a * pr0 + cos_a * pc0)
-            spc0 = <Py_ssize_t>round(cos_a * pr0 - sin_a * pc0)
-            spr1 = <Py_ssize_t>round(sin_a * pr1 + cos_a * pc1)
-            spc1 = <Py_ssize_t>round(cos_a * pr1 - sin_a * pc1)
+                spr0 = <Py_ssize_t>round(sin_a * pr0 + cos_a * pc0)
+                spc0 = <Py_ssize_t>round(cos_a * pr0 - sin_a * pc0)
+                spr1 = <Py_ssize_t>round(sin_a * pr1 + cos_a * pc1)
+                spc1 = <Py_ssize_t>round(cos_a * pr1 - sin_a * pc1)
 
-            if image[kr + spr0, kc + spc0] < image[kr + spr1, kc + spc1]:
-                descriptors[i, j] = True
+                if image[kr + spr0, kc + spc0] < image[kr + spr1, kc + spc1]:
+                    descriptors[i, j] = True
 
     return np.asarray(descriptors)
diff --git a/skimage/feature/tests/test_orb.py b/skimage/feature/tests/test_orb.py
index 5bed2bf3..8895d857 100644
--- a/skimage/feature/tests/test_orb.py
+++ b/skimage/feature/tests/test_orb.py
@@ -3,11 +3,13 @@ from numpy.testing import assert_equal, assert_almost_equal, run_module_suite
 from skimage.feature import ORB
 from skimage import data
 from skimage.color import rgb2gray
+from skimage._shared.testing import test_parallel
 
 
 img = rgb2gray(data.lena())
 
 
+@test_parallel()
 def test_keypoints_orb_desired_no_of_keypoints():
     detector_extractor = ORB(n_keypoints=10, fast_n=12, fast_threshold=0.20)
     detector_extractor.detect(img)