From 08a9448167cf4057215e271a55d713be4e479f85 Mon Sep 17 00:00:00 2001
From: CalWelsh <cwelsh@sbacademy.org>
Date: Sat, 28 Aug 2021 15:37:25 -0500
Subject: [PATCH 1/3] Update pyav_reader.py to make generator threadsafe

I had an issue where code using pyav_reader.py would randomly break and throw a "ValueError: Generator Already Executing Error"; the stack indicated that the function _gen_frames was the culprit; I added a function and a decorator (line for line copied from the sources below with one change, re-naming "next" to "__next__") that makes a non-threadsafe generator threadsafe. This resolved the issue on both Windows and Mac.

Sources:
https://anandology.com/blog/using-iterators-and-generators/
https://stackoverflow.com/questions/41194726/python-generator-thread-safety-using-keras
---
 pims/pyav_reader.py | 24 +++++++++++++++++++++++-
 1 file changed, 23 insertions(+), 1 deletion(-)

diff --git a/pims/pyav_reader.py b/pims/pyav_reader.py
index 2b453ee..7776075 100644
--- a/pims/pyav_reader.py
+++ b/pims/pyav_reader.py
@@ -27,6 +27,28 @@ def _next_video_packet(container_iter):
     raise ValueError("Could not find any video packets.")
 
 
+class threadsafe_iter:
+    """Takes an iterator/generator and makes it thread-safe by
+    serializing call to the `next` method of given iterator/generator.
+    """
+    def __init__(self, it):
+        self.it = it
+        self.lock = threading.Lock()
+
+    def __iter__(self):
+        return self
+
+    def __next__(self):
+        with self.lock:
+            return self.it.next()
+          
+def threadsafe_generator(f):
+    """A decorator that takes a generator function and makes it thread-safe.
+    """
+    def g(*a, **kw):
+        return threadsafe_iter(f(*a, **kw))
+    return g
+          
 class WrapPyAvFrame(object):
     def __init__(self, frame, frame_no, metadata=None):
         self.frame_no = frame_no
@@ -46,7 +68,7 @@ def to_frame(self):
                              frame_no=self.frame_no, metadata=self.metadata)
         return self.arr
 
-
+@threadsafe_generator
 def _gen_frames(demuxer, time_base, frame_rate=1., first_pts=0):
     for packet in demuxer:
         for frame in packet.decode():

From 2ed0ac89a2d53857925e793540cf3120cd2d3ea1 Mon Sep 17 00:00:00 2001
From: Callum Welsh <cwelsh@sbacademy.org>
Date: Sat, 28 Aug 2021 19:23:31 -0500
Subject: [PATCH 2/3] Update pyav_reader.py

---
 pims/pyav_reader.py | 1 +
 1 file changed, 1 insertion(+)

diff --git a/pims/pyav_reader.py b/pims/pyav_reader.py
index 7776075..17ebdfd 100644
--- a/pims/pyav_reader.py
+++ b/pims/pyav_reader.py
@@ -2,6 +2,7 @@
                         unicode_literals)
 
 import numpy as np
+import threading
 
 from pims.base_frames import FramesSequence
 from pims.frame import Frame

From 53f2518ed01b5b651bfa759685fd25c19a9518c2 Mon Sep 17 00:00:00 2001
From: Callum Welsh <cwelsh@sbacademy.org>
Date: Tue, 7 Sep 2021 13:30:04 -0500
Subject: [PATCH 3/3] Changed self.it.next() to next(self.it) to prevent error

Sometimes the self.it.next() method was breaking; looks like that method might be an artifact of older versions of Python? Fixed it to modern spec to prevent future errors.
---
 pims/pyav_reader.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/pims/pyav_reader.py b/pims/pyav_reader.py
index 17ebdfd..40caa1e 100644
--- a/pims/pyav_reader.py
+++ b/pims/pyav_reader.py
@@ -41,7 +41,7 @@ def __iter__(self):
 
     def __next__(self):
         with self.lock:
-            return self.it.next()
+            return next(self.it)
           
 def threadsafe_generator(f):
     """A decorator that takes a generator function and makes it thread-safe.