diff -Naur orig/src/idiff/idiff.cpp external_openimageio/src/idiff/idiff.cpp
--- orig/src/idiff/idiff.cpp	2023-06-07 07:47:42 -0600
+++ external_openimageio/src/idiff/idiff.cpp	2023-06-07 09:46:47 -0600
@@ -399,5 +399,6 @@
 
     imagecache->invalidate_all(true);
     ImageCache::destroy(imagecache);
+    default_thread_pool()->resize(0);
     return ret;
 }
diff -Naur orig/src/libutil/thread.cpp external_openimageio/src/libutil/thread.cpp
--- orig/src/libutil/thread.cpp	2023-06-07 07:47:42 -0600
+++ external_openimageio/src/libutil/thread.cpp	2023-06-07 09:45:39 -0600
@@ -151,9 +151,10 @@
                     this->set_thread(i);
                 }
             } else {  // the number of threads is decreased
+                std::vector<std::unique_ptr<std::thread>> terminating_threads;
                 for (int i = oldNThreads - 1; i >= nThreads; --i) {
                     *this->flags[i] = true;  // this thread will finish
-                    this->terminating_threads.push_back(
+                    terminating_threads.push_back(
                         std::move(this->threads[i]));
                     this->threads.erase(this->threads.begin() + i);
                 }
@@ -162,6 +163,11 @@
                     std::unique_lock<std::mutex> lock(this->mutex);
                     this->cv.notify_all();
                 }
+                // wait for the terminated threads to finish
+                for (auto& thread : terminating_threads) {
+                    if (thread->joinable())
+                        thread->join();
+                }
                 this->threads.resize(
                     nThreads);  // safe to delete because the threads are detached
                 this->flags.resize(
@@ -238,16 +244,10 @@
             if (thread->joinable())
                 thread->join();
         }
-        // wait for the terminated threads to finish
-        for (auto& thread : this->terminating_threads) {
-            if (thread->joinable())
-                thread->join();
-        }
         // if there were no threads in the pool but some functors in the queue, the functors are not deleted by the threads
         // therefore delete them here
         this->clear_queue();
         this->threads.clear();
-        this->terminating_threads.clear();
         this->flags.clear();
     }
 
@@ -349,7 +349,6 @@
     }
 
     std::vector<std::unique_ptr<std::thread>> threads;
-    std::vector<std::unique_ptr<std::thread>> terminating_threads;
     std::vector<std::shared_ptr<std::atomic<bool>>> flags;
     mutable pvt::ThreadsafeQueue<std::function<void(int id)>*> q;
     std::atomic<bool> isDone;