diff --git a/src/lib/IlmThread/CMakeLists.txt b/src/lib/IlmThread/CMakeLists.txt
index b87da8ac68..f2ebc95cc4 100644
--- a/src/lib/IlmThread/CMakeLists.txt
+++ b/src/lib/IlmThread/CMakeLists.txt
@@ -19,6 +19,7 @@ openexr_define_library(IlmThread
     IlmThreadMutex.h
     IlmThreadNamespace.h
     IlmThreadPool.h
+    IlmThreadProcessGroup.h
     IlmThreadSemaphore.h
   DEPENDENCIES
     OpenEXR::Config
diff --git a/src/lib/IlmThread/IlmThreadProcessGroup.h b/src/lib/IlmThread/IlmThreadProcessGroup.h
new file mode 100644
index 0000000000..8ef677a658
--- /dev/null
+++ b/src/lib/IlmThread/IlmThreadProcessGroup.h
@@ -0,0 +1,154 @@
+//
+// SPDX-License-Identifier: BSD-3-Clause
+// Copyright (c) Contributors to the OpenEXR Project.
+//
+
+#ifndef INCLUDED_ILM_THREAD_PROCESS_GROUP_H
+#define INCLUDED_ILM_THREAD_PROCESS_GROUP_H
+
+//-----------------------------------------------------------------------------
+//
+// Class ProcessGroup is a templated inline helper for constraining
+// task contexts to a number of threads. It maintains a list of
+// contexts and then can hand them out one at a time, waiting for a
+// previous thread request to finish before handing out more,
+// preventing over-subscription / allocation of contexts.
+//
+//-----------------------------------------------------------------------------
+
+#include "IlmThreadConfig.h"
+#include "IlmThreadExport.h"
+#include "IlmThreadNamespace.h"
+#include "IlmThreadSemaphore.h"
+
+#include "Iex.h"
+
+#include <atomic>
+#include <string>
+#include <type_traits>
+#include <vector>
+
+ILMTHREAD_INTERNAL_NAMESPACE_HEADER_ENTER
+
+template <typename P,
+    std::enable_if_t <
+        std::is_default_constructible <P>::value &&
+        std::is_same <decltype (P {}.next), P *>::value, bool> = true>
+class ProcessGroup
+{
+public:
+    using Process = P;
+
+    ProcessGroup (unsigned int numThreads)
+        : _sem (numThreads)
+        , _avail_head (nullptr)
+        , _first_failure (nullptr)
+    {
+        _fixed_pool.resize (numThreads);
+        for ( unsigned int i = 0; i < numThreads; ++i )
+        {
+            if (i == (numThreads - 1))
+                _fixed_pool[i].next = nullptr;
+            else
+                _fixed_pool[i].next = &(_fixed_pool[i+1]);
+        }
+        _avail_head = &(_fixed_pool[0]);
+    }
+
+    ProcessGroup (const ProcessGroup&) = delete;
+    ProcessGroup& operator= (const ProcessGroup&) = delete;
+    ProcessGroup (ProcessGroup&&) = default;
+    ProcessGroup& operator= (ProcessGroup&&) = delete;
+    ~ProcessGroup()
+    {
+        std::string *cur = _first_failure.load ();
+        delete cur;
+    }
+
+    void push (Process *p)
+    {
+        Process* oldhead = _avail_head.load (std::memory_order_relaxed);
+
+        do
+        {
+            p->next = oldhead;
+        } while (!_avail_head.compare_exchange_weak (
+                     oldhead, p,
+                     std::memory_order_release,
+                     std::memory_order_relaxed));
+
+        // notify someone else there's one available
+        _sem.post ();
+    }
+
+    // called by the thread dispatching work units, may block
+    Process* pop ()
+    {
+        Process* ret = nullptr;
+
+        // we do not have to worry about ABA problems as
+        // we have a static pool of items we own, we're just
+        // putting them here and popping them off.
+
+        // used for honoring the numThreads, as pop
+        // should only be called by the one thread
+        // waiting to submit thread calls
+        _sem.wait ();
+
+        ret = _avail_head.load (std::memory_order_acquire);
+
+        Process* newhead;
+        do
+        {
+            if (!ret)
+                std::cerr << "GACK: serious failure case???" << std::endl;
+
+            newhead = ret->next;
+        } while ( !_avail_head.compare_exchange_weak(
+                      ret, newhead, std::memory_order_acquire));
+
+        return ret;
+    }
+
+    void record_failure (const char *e)
+    {
+        // should we construct a list of failures if there are
+        // more than one? seems less confusing to just report
+        // the first we happened to record
+
+        std::string *cur = _first_failure.load ();
+        if (!cur)
+        {
+            std::string *msg = new std::string (e);
+            if (! _first_failure.compare_exchange_strong (cur, msg))
+                delete msg;
+        }
+    }
+
+    void throw_on_failure ()
+    {
+        std::string *cur = _first_failure.load ();
+        _first_failure.store (nullptr);
+
+        if (cur)
+        {
+            std::string msg (*cur);
+            delete cur;
+
+            throw IEX_NAMESPACE::IoExc (msg);
+        }
+    }
+private:
+    Semaphore _sem;
+
+    std::vector<Process>   _fixed_pool;
+
+    std::atomic<Process *> _avail_head;
+
+    std::atomic<std::string *> _first_failure;
+};
+
+
+ILMTHREAD_INTERNAL_NAMESPACE_HEADER_EXIT
+
+#endif // INCLUDED_ILM_THREAD_POOL_H
diff --git a/src/lib/OpenEXR/ImfDeepScanLineInputFile.cpp b/src/lib/OpenEXR/ImfDeepScanLineInputFile.cpp
index 31ec5ad667..1487249622 100644
--- a/src/lib/OpenEXR/ImfDeepScanLineInputFile.cpp
+++ b/src/lib/OpenEXR/ImfDeepScanLineInputFile.cpp
@@ -16,14 +16,14 @@
 
 #include "IlmThreadPool.h"
 #if ILMTHREAD_THREADING_ENABLED
-#    include "IlmThreadSemaphore.h"
+#    include "IlmThreadProcessGroup.h"
+#    include <mutex>
 #endif
 
 #include "Iex.h"
 
 #include <algorithm>
 #include <limits>
-#include <mutex>
 #include <string>
 #include <vector>
 
@@ -86,9 +86,13 @@ struct ScanLineProcess
     exr_chunk_info_t      cinfo;
     exr_decode_pipeline_t decoder;
 
-    std::shared_ptr<ScanLineProcess> next;
+    ScanLineProcess*      next;
 };
 
+#if ILMTHREAD_THREADING_ENABLED
+using ScanLineProcessGroup = ILMTHREAD_NAMESPACE::ProcessGroup<ScanLineProcess>;
+#endif
+
 } // empty namespace
 
 struct DeepScanLineInputFile::Data
@@ -97,9 +101,6 @@ struct DeepScanLineInputFile::Data
     : _ctxt (ctxt)
     , partNumber (pN)
     , numThreads (nT)
-#if ILMTHREAD_THREADING_ENABLED
-    , _sem ((unsigned int)nT)
-#endif
     {}
 
     void initialize ()
@@ -133,42 +134,16 @@ struct DeepScanLineInputFile::Data
     DeepFrameBuffer frameBuffer;
     std::vector<DeepSlice> fill_list;
 
-    std::shared_ptr<ScanLineProcess> processStack;
-    std::shared_ptr<ScanLineProcess> getChunkProcess ()
-    {
-        std::shared_ptr<ScanLineProcess> retval;
-#if ILMTHREAD_THREADING_ENABLED
-        std::lock_guard<std::mutex> lk (_mx);
-#endif
-        retval = processStack;
-        if (!retval)
-            retval = std::make_shared<ScanLineProcess> ();
-        processStack = retval->next;
-        retval->next.reset();
-        return retval;
-    }
-    void putChunkProcess (std::shared_ptr<ScanLineProcess> sp)
-    {
-#if ILMTHREAD_THREADING_ENABLED
-        std::lock_guard<std::mutex> lk (_mx);
-#endif
-        sp->next = processStack;
-        processStack = sp;
-    }
-
 #if ILMTHREAD_THREADING_ENABLED
     std::mutex _mx;
-    ILMTHREAD_NAMESPACE::Semaphore _sem;
 
-    std::vector<std::string> _failures;
-#endif
-#if ILMTHREAD_THREADING_ENABLED
     class LineBufferTask final : public ILMTHREAD_NAMESPACE::Task
     {
     public:
         LineBufferTask (
             ILMTHREAD_NAMESPACE::TaskGroup* group,
             Data*                   ifd,
+            ScanLineProcessGroup*   lineg,
             const DeepFrameBuffer*  outfb,
             const exr_chunk_info_t& cinfo,
             int                     fby,
@@ -179,7 +154,8 @@ struct DeepScanLineInputFile::Data
             , _ifd (ifd)
             , _fby (fby)
             , _last_fby (endScan)
-            , _line (ifd->getChunkProcess ())
+            , _line (lineg->pop ())
+            , _line_group (lineg)
         {
             _line->cinfo = cinfo;
             _line->counts_only = countsOnly;
@@ -187,9 +163,7 @@ struct DeepScanLineInputFile::Data
 
         ~LineBufferTask () override
         {
-            if (_line)
-                _ifd->putChunkProcess (std::move (_line));
-            _ifd->_sem.post ();
+            _line_group->push (_line);
         }
 
         void execute () override;
@@ -201,8 +175,8 @@ struct DeepScanLineInputFile::Data
         Data*                  _ifd;
         int                    _fby;
         int                    _last_fby;
-
-        std::shared_ptr<ScanLineProcess> _line;
+        ScanLineProcess*       _line;
+        ScanLineProcessGroup*  _line_group;
     };
 #endif
 };
@@ -301,7 +275,6 @@ DeepScanLineInputFile::setFrameBuffer (const DeepFrameBuffer& frameBuffer)
     _data->prepFillList (frameBuffer, _data->fill_list);
     _data->frameBuffer = frameBuffer;
     _data->frameBufferValid = true;
-    _data->processStack.reset();
 }
 
 const DeepFrameBuffer&
@@ -539,29 +512,36 @@ DeepScanLineInputFile::Data::readData (
 
     if (nchunks > 1 && numThreads > 1)
     {
-        ILMTHREAD_NAMESPACE::TaskGroup tg;
+        // we need the lifetime of this to last longer than the
+        // lifetime of the task group below such that we don't get use
+        // after free type error, so use scope rules to accomplish
+        // this
+        ScanLineProcessGroup sg (numThreads);
 
-        for (int y = scanLine1; y <= scanLine2; )
         {
-            if (EXR_ERR_SUCCESS != exr_read_scanline_chunk_info (*_ctxt, partNumber, y, &cinfo))
-                throw IEX_NAMESPACE::InputExc ("Unable to query scanline information");
+            ILMTHREAD_NAMESPACE::TaskGroup tg;
 
-            // used for honoring the numThreads
-            _sem.wait ();
+            for (int y = scanLine1; y <= scanLine2; )
+            {
+                if (EXR_ERR_SUCCESS != exr_read_scanline_chunk_info (*_ctxt, partNumber, y, &cinfo))
+                    throw IEX_NAMESPACE::InputExc ("Unable to query scanline information");
 
-            ILMTHREAD_NAMESPACE::ThreadPool::addGlobalTask (
-                new LineBufferTask (&tg, this, &fb, cinfo, y, scanLine2, countsOnly) );
+                ILMTHREAD_NAMESPACE::ThreadPool::addGlobalTask (
+                    new LineBufferTask (&tg, this, &sg, &fb, cinfo, y, scanLine2, countsOnly) );
 
-            y += scansperchunk - (y - cinfo.start_y);
+                y += scansperchunk - (y - cinfo.start_y);
+            }
         }
+
+        sg.throw_on_failure ();
     }
     else
 #endif
     {
-        auto sp = getChunkProcess ();
-        bool redo = sp->first || sp->counts_only != countsOnly;
+        ScanLineProcess sp;
+        bool redo = true;
 
-        sp->counts_only = countsOnly;
+        sp.counts_only = countsOnly;
         for (int y = scanLine1; y <= scanLine2; )
         {
             if (EXR_ERR_SUCCESS != exr_read_scanline_chunk_info (*_ctxt, partNumber, y, &cinfo))
@@ -571,10 +551,10 @@ DeepScanLineInputFile::Data::readData (
             // re-run the unpack (i.e. people reading 1 scan at a time
             // in a multi-scanline chunk)
             if (!redo &&
-                sp->cinfo.idx == cinfo.idx &&
-                sp->last_decode_err == EXR_ERR_SUCCESS)
+                sp.cinfo.idx == cinfo.idx &&
+                sp.last_decode_err == EXR_ERR_SUCCESS)
             {
-                sp->run_unpack (
+                sp.run_unpack (
                     *_ctxt,
                     partNumber,
                     &fb,
@@ -584,8 +564,8 @@ DeepScanLineInputFile::Data::readData (
             }
             else
             {
-                sp->cinfo = cinfo;
-                sp->run_decode (
+                sp.cinfo = cinfo;
+                sp.run_decode (
                     *_ctxt,
                     partNumber,
                     &fb,
@@ -597,19 +577,7 @@ DeepScanLineInputFile::Data::readData (
 
             y += scansperchunk - (y - cinfo.start_y);
         }
-
-        putChunkProcess (std::move(sp));
-    }
-
-#if ILMTHREAD_THREADING_ENABLED
-    std::lock_guard<std::mutex> lock (_mx);
-    if (! _failures.empty())
-    {
-        std::string fail = _failures[0];
-        _failures.clear ();
-        throw IEX_NAMESPACE::IoExc (fail);
     }
-#endif
 }
 
 ////////////////////////////////////////
@@ -727,8 +695,11 @@ void DeepScanLineInputFile::Data::LineBufferTask::execute ()
     }
     catch (std::exception &e)
     {
-        std::lock_guard<std::mutex> lock (_ifd->_mx);
-        _ifd->_failures.emplace_back (std::string (e.what()));
+        _line_group->record_failure (e.what ());
+    }
+    catch (...)
+    {
+        _line_group->record_failure ("Unknown exception");
     }
 }
 #endif
diff --git a/src/lib/OpenEXR/ImfDeepTiledInputFile.cpp b/src/lib/OpenEXR/ImfDeepTiledInputFile.cpp
index 90de89ca75..3ce47b98eb 100644
--- a/src/lib/OpenEXR/ImfDeepTiledInputFile.cpp
+++ b/src/lib/OpenEXR/ImfDeepTiledInputFile.cpp
@@ -15,7 +15,8 @@
 
 #include "IlmThreadPool.h"
 #if ILMTHREAD_THREADING_ENABLED
-#    include "IlmThreadSemaphore.h"
+#    include "IlmThreadProcessGroup.h"
+#    include <mutex>
 #endif
 
 #include "ImfDeepFrameBuffer.h"
@@ -26,7 +27,6 @@
 #include "ImfTiledMisc.h"
 
 #include <algorithm>
-#include <mutex>
 #include <string>
 #include <vector>
 
@@ -71,9 +71,13 @@ struct TileProcess
     exr_chunk_info_t      cinfo;
     exr_decode_pipeline_t decoder;
 
-    std::shared_ptr<TileProcess> next;
+    TileProcess*          next;
 };
 
+#if ILMTHREAD_THREADING_ENABLED
+using TileProcessGroup = ILMTHREAD_NAMESPACE::ProcessGroup<TileProcess>;
+#endif
+
 } // empty namespace
 
 //
@@ -87,9 +91,6 @@ struct DeepTiledInputFile::Data
     : _ctxt (ctxt)
     , partNumber (pN)
     , numThreads (nT)
-#if ILMTHREAD_THREADING_ENABLED
-    , _sem ((unsigned int)nT)
-#endif
     {}
 
     void initialize ()
@@ -136,49 +137,23 @@ struct DeepTiledInputFile::Data
     std::vector<DeepSlice> fill_list;
 
 #if ILMTHREAD_THREADING_ENABLED
-    std::vector<std::string> _failures;
-
     std::mutex _mx;
-    ILMTHREAD_NAMESPACE::Semaphore _sem;
-#endif
-
-    std::shared_ptr<TileProcess> processStack;
-    std::shared_ptr<TileProcess> getChunkProcess ()
-    {
-        std::shared_ptr<TileProcess> retval;
-#if ILMTHREAD_THREADING_ENABLED
-        std::lock_guard<std::mutex> lk (_mx);
-#endif
-        retval = processStack;
-        if (!retval)
-            retval = std::make_shared<TileProcess> ();
-        processStack = retval->next;
-        retval->next.reset();
-        return retval;
-    }
-    void putChunkProcess (std::shared_ptr<TileProcess> tp)
-    {
-#if ILMTHREAD_THREADING_ENABLED
-        std::lock_guard<std::mutex> lk (_mx);
-#endif
-        tp->next = processStack;
-        processStack = tp;
-    }
 
-#if ILMTHREAD_THREADING_ENABLED
     class TileBufferTask final : public ILMTHREAD_NAMESPACE::Task
     {
     public:
         TileBufferTask (
             ILMTHREAD_NAMESPACE::TaskGroup* group,
             Data*                   ifd,
+            TileProcessGroup*       tileg,
             const DeepFrameBuffer*  outfb,
             const exr_chunk_info_t& cinfo,
             bool                    countsOnly)
             : Task (group)
             , _outfb (outfb)
             , _ifd (ifd)
-            , _tile (ifd->getChunkProcess ())
+            , _tile (tileg->pop ())
+            , _tile_group (tileg)
         {
             _tile->cinfo = cinfo;
             _tile->counts_only = countsOnly;
@@ -186,9 +161,7 @@ struct DeepTiledInputFile::Data
 
         ~TileBufferTask () override
         {
-            if (_tile)
-                _ifd->putChunkProcess (std::move (_tile));
-            _ifd->_sem.post ();
+            _tile_group->push (_tile);
         }
 
         void execute () override;
@@ -199,7 +172,8 @@ struct DeepTiledInputFile::Data
         const DeepFrameBuffer* _outfb;
         Data*                  _ifd;
 
-        std::shared_ptr<TileProcess> _tile;
+        TileProcess*       _tile;
+        TileProcessGroup*  _tile_group;
     };
 #endif
 };
@@ -307,7 +281,6 @@ DeepTiledInputFile::setFrameBuffer (const DeepFrameBuffer& frameBuffer)
 
     _data->frameBuffer = frameBuffer;
     _data->frameBufferValid = true;
-    _data->processStack.reset();
 }
 
 const DeepFrameBuffer&
@@ -924,38 +897,45 @@ void DeepTiledInputFile::Data::readTiles (
 #if ILMTHREAD_THREADING_ENABLED
     if (nTiles > 1 && numThreads > 1)
     {
-        ILMTHREAD_NAMESPACE::TaskGroup tg;
+        // we need the lifetime of this to last longer than the
+        // lifetime of the task group below such that we don't get use
+        // after free type error, so use scope rules to accomplish
+        // this
+        TileProcessGroup tpg (numThreads);
 
-        for (int ty = dy1; ty <= dy2; ++ty)
         {
-            for (int tx = dx1; tx <= dx2; ++tx)
+            ILMTHREAD_NAMESPACE::TaskGroup tg;
+
+            for (int ty = dy1; ty <= dy2; ++ty)
             {
-                exr_result_t rv = exr_read_tile_chunk_info (
-                    *_ctxt, partNumber, tx, ty, lx, ly, &cinfo);
-                if (EXR_ERR_INCOMPLETE_CHUNK_TABLE == rv)
+                for (int tx = dx1; tx <= dx2; ++tx)
                 {
-                    THROW (
-                        IEX_NAMESPACE::InputExc,
-                        "Tile (" << tx << ", " << ty << ", " << lx << ", " << ly
-                        << ") is missing.");
-                }
-                else if (EXR_ERR_SUCCESS != rv)
-                    throw IEX_NAMESPACE::InputExc ("Unable to query tile information");
-
-                // used for honoring the numThreads
-                _sem.wait ();
+                    exr_result_t rv = exr_read_tile_chunk_info (
+                        *_ctxt, partNumber, tx, ty, lx, ly, &cinfo);
+                    if (EXR_ERR_INCOMPLETE_CHUNK_TABLE == rv)
+                    {
+                        THROW (
+                            IEX_NAMESPACE::InputExc,
+                            "Tile (" << tx << ", " << ty << ", " << lx << ", " << ly
+                            << ") is missing.");
+                    }
+                    else if (EXR_ERR_SUCCESS != rv)
+                        throw IEX_NAMESPACE::InputExc ("Unable to query tile information");
 
-                ILMTHREAD_NAMESPACE::ThreadPool::addGlobalTask (
-                    new TileBufferTask (&tg, this, &frameBuffer, cinfo, countsOnly) );
+                    ILMTHREAD_NAMESPACE::ThreadPool::addGlobalTask (
+                        new TileBufferTask (&tg, this, &tpg, &frameBuffer, cinfo, countsOnly) );
+                }
             }
         }
+
+        tpg.throw_on_failure ();
     }
     else
 #endif
     {
-        auto tp = getChunkProcess ();
+        TileProcess tp;
 
-        tp->counts_only = countsOnly;
+        tp.counts_only = countsOnly;
         for (int ty = dy1; ty <= dy2; ++ty)
         {
             for (int tx = dx1; tx <= dx2; ++tx)
@@ -972,26 +952,15 @@ void DeepTiledInputFile::Data::readTiles (
                 else if (EXR_ERR_SUCCESS != rv)
                     throw IEX_NAMESPACE::InputExc ("Unable to query tile information");
 
-                tp->cinfo = cinfo;
-                tp->run_decode (
+                tp.cinfo = cinfo;
+                tp.run_decode (
                     *_ctxt,
                     partNumber,
                     &frameBuffer,
                     fill_list);
             }
         }
-
-        putChunkProcess (std::move(tp));
-    }
-
-#if ILMTHREAD_THREADING_ENABLED
-    if (! _failures.empty())
-    {
-        std::string fail = _failures[0];
-        _failures.clear ();
-        throw IEX_NAMESPACE::IoExc (fail);
     }
-#endif
 }
 
 ////////////////////////////////////////
@@ -1009,8 +978,11 @@ void DeepTiledInputFile::Data::TileBufferTask::execute ()
     }
     catch (std::exception &e)
     {
-        std::lock_guard<std::mutex> lock (_ifd->_mx);
-        _ifd->_failures.emplace_back (std::string (e.what()));
+        _tile_group->record_failure (e.what ());
+    }
+    catch (...)
+    {
+        _tile_group->record_failure ("Unknown exception");
     }
 }
 #endif
diff --git a/src/lib/OpenEXR/ImfScanLineInputFile.cpp b/src/lib/OpenEXR/ImfScanLineInputFile.cpp
index f7eb144701..e0db6de0b9 100644
--- a/src/lib/OpenEXR/ImfScanLineInputFile.cpp
+++ b/src/lib/OpenEXR/ImfScanLineInputFile.cpp
@@ -15,13 +15,13 @@
 
 #include "IlmThreadPool.h"
 #if ILMTHREAD_THREADING_ENABLED
-#    include "IlmThreadSemaphore.h"
+#    include "IlmThreadProcessGroup.h"
+#    include <mutex>
 #endif
 
 #include "ImfFrameBuffer.h"
 #include "ImfInputPartData.h"
 
-#include <mutex>
 #include <vector>
 
 OPENEXR_IMF_INTERNAL_NAMESPACE_SOURCE_ENTER
@@ -67,9 +67,14 @@ struct ScanLineProcess
     exr_chunk_info_t      cinfo;
     exr_decode_pipeline_t decoder;
 
-    std::shared_ptr<ScanLineProcess> next;
+    // requirement to use process group
+    ScanLineProcess* next;
 };
 
+#if ILMTHREAD_THREADING_ENABLED
+using ScanLineProcessGroup = ILMTHREAD_NAMESPACE::ProcessGroup<ScanLineProcess>;
+#endif
+
 } // empty namespace
 
 struct ScanLineInputFile::Data
@@ -78,9 +83,6 @@ struct ScanLineInputFile::Data
     : _ctxt (ctxt)
     , partNumber (pN)
     , numThreads (nT)
-#if ILMTHREAD_THREADING_ENABLED
-    , _sem ((unsigned int)nT)
-#endif
     {}
 
     void initialize ()
@@ -105,41 +107,14 @@ struct ScanLineInputFile::Data
 
 #if ILMTHREAD_THREADING_ENABLED
     std::mutex _mx;
-    ILMTHREAD_NAMESPACE::Semaphore _sem;
 
-    std::vector<std::string> _failures;
-#endif
-
-    std::shared_ptr<ScanLineProcess> processStack;
-    std::shared_ptr<ScanLineProcess> getChunkProcess ()
-    {
-        std::shared_ptr<ScanLineProcess> retval;
-#if ILMTHREAD_THREADING_ENABLED
-        std::lock_guard<std::mutex> lk (_mx);
-#endif
-        retval = processStack;
-        if (!retval)
-            retval = std::make_shared<ScanLineProcess> ();
-        processStack = retval->next;
-        retval->next.reset();
-        return retval;
-    }
-    void putChunkProcess (std::shared_ptr<ScanLineProcess> sp)
-    {
-#if ILMTHREAD_THREADING_ENABLED
-        std::lock_guard<std::mutex> lk (_mx);
-#endif
-        sp->next = processStack;
-        processStack = std::move (sp);
-    }
-
-#if ILMTHREAD_THREADING_ENABLED
     class LineBufferTask final : public ILMTHREAD_NAMESPACE::Task
     {
     public:
         LineBufferTask (
             ILMTHREAD_NAMESPACE::TaskGroup* group,
             Data*                   ifd,
+            ScanLineProcessGroup*   lineg,
             const FrameBuffer*      outfb,
             const exr_chunk_info_t& cinfo,
             int                     fby,
@@ -149,16 +124,15 @@ struct ScanLineInputFile::Data
             , _ifd (ifd)
             , _fby (fby)
             , _last_fby (endScan)
-            , _line (ifd->getChunkProcess ())
+            , _line (lineg->pop ())
+            , _line_group (lineg)
         {
             _line->cinfo = cinfo;
         }
 
         ~LineBufferTask () override
         {
-            if (_line)
-                _ifd->putChunkProcess (std::move (_line));
-            _ifd->_sem.post ();
+            _line_group->push (_line);
         }
 
         void execute () override;
@@ -166,12 +140,12 @@ struct ScanLineInputFile::Data
     private:
         void run_decode ();
 
-        const FrameBuffer* _outfb;
-        Data*              _ifd;
-        int                _fby;
-        int                _last_fby;
-
-        std::shared_ptr<ScanLineProcess> _line;
+        const FrameBuffer*    _outfb;
+        Data*                 _ifd;
+        int                   _fby;
+        int                   _last_fby;
+        ScanLineProcess*      _line;
+        ScanLineProcessGroup* _line_group;
     };
 #endif
 };
@@ -279,7 +253,6 @@ ScanLineInputFile::setFrameBuffer (const FrameBuffer& frameBuffer)
     }
 
     _data->frameBuffer = frameBuffer;
-    _data->processStack.reset();
 }
 
 const FrameBuffer&
@@ -445,26 +418,33 @@ void ScanLineInputFile::Data::readPixels (
 
     if (nchunks > 1 && numThreads > 1)
     {
-        ILMTHREAD_NAMESPACE::TaskGroup tg;
+        // we need the lifetime of this to last longer than the
+        // lifetime of the task group below such that we don't get use
+        // after free type error, so use scope rules to accomplish
+        // this
+        ScanLineProcessGroup sg (numThreads);
 
-        for (int y = scanLine1; y <= scanLine2; )
         {
-            if (EXR_ERR_SUCCESS != exr_read_scanline_chunk_info (*_ctxt, partNumber, y, &cinfo))
-                throw IEX_NAMESPACE::InputExc ("Unable to query scanline information");
+            ILMTHREAD_NAMESPACE::TaskGroup tg;
 
-            // used for honoring the numThreads
-            _sem.wait ();
+            for (int y = scanLine1; y <= scanLine2; )
+            {
+                if (EXR_ERR_SUCCESS != exr_read_scanline_chunk_info (*_ctxt, partNumber, y, &cinfo))
+                    throw IEX_NAMESPACE::InputExc ("Unable to query scanline information");
 
-            ILMTHREAD_NAMESPACE::ThreadPool::addGlobalTask (
-                new LineBufferTask (&tg, this, &fb, cinfo, y, scanLine2) );
+                ILMTHREAD_NAMESPACE::ThreadPool::addGlobalTask (
+                    new LineBufferTask (&tg, this, &sg, &fb, cinfo, y, scanLine2) );
 
-            y += scansperchunk - (y - cinfo.start_y);
+                y += scansperchunk - (y - cinfo.start_y);
+            }
         }
+
+        sg.throw_on_failure ();
     }
     else
 #endif
     {
-        auto sp = getChunkProcess ();
+        ScanLineProcess sp;
 
         for (int y = scanLine1; y <= scanLine2; )
         {
@@ -474,10 +454,10 @@ void ScanLineInputFile::Data::readPixels (
             // check if we have the same chunk where we can just
             // re-run the unpack (i.e. people reading 1 scan at a time
             // in a multi-scanline chunk)
-            if (!sp->first && sp->cinfo.idx == cinfo.idx &&
-                sp->last_decode_err == EXR_ERR_SUCCESS)
+            if (!sp.first && sp.cinfo.idx == cinfo.idx &&
+                sp.last_decode_err == EXR_ERR_SUCCESS)
             {
-                sp->run_unpack (
+                sp.run_unpack (
                     *_ctxt,
                     partNumber,
                     &fb,
@@ -487,8 +467,8 @@ void ScanLineInputFile::Data::readPixels (
             }
             else
             {
-                sp->cinfo = cinfo;
-                sp->run_decode (
+                sp.cinfo = cinfo;
+                sp.run_decode (
                     *_ctxt,
                     partNumber,
                     &fb,
@@ -499,19 +479,7 @@ void ScanLineInputFile::Data::readPixels (
 
             y += scansperchunk - (y - cinfo.start_y);
         }
-
-        putChunkProcess (std::move(sp));
-    }
-
-#if ILMTHREAD_THREADING_ENABLED
-    std::lock_guard<std::mutex> lock (_mx);
-    if (! _failures.empty())
-    {
-        std::string fail = _failures[0];
-        _failures.clear ();
-        throw IEX_NAMESPACE::IoExc (fail);
     }
-#endif
 }
 
 ////////////////////////////////////////
@@ -531,8 +499,11 @@ void ScanLineInputFile::Data::LineBufferTask::execute ()
     }
     catch (std::exception &e)
     {
-        std::lock_guard<std::mutex> lock (_ifd->_mx);
-        _ifd->_failures.emplace_back (std::string (e.what()));
+        _line_group->record_failure (e.what ());
+    }
+    catch (...)
+    {
+        _line_group->record_failure ("Unknown exception");
     }
 }
 #endif
diff --git a/src/lib/OpenEXR/ImfTiledInputFile.cpp b/src/lib/OpenEXR/ImfTiledInputFile.cpp
index d37115312d..7bf4c5ebe1 100644
--- a/src/lib/OpenEXR/ImfTiledInputFile.cpp
+++ b/src/lib/OpenEXR/ImfTiledInputFile.cpp
@@ -15,7 +15,8 @@
 
 #include "IlmThreadPool.h"
 #if ILMTHREAD_THREADING_ENABLED
-#    include "IlmThreadSemaphore.h"
+#    include "IlmThreadProcessGroup.h"
+#    include <mutex>
 #endif
 
 #include "ImfFrameBuffer.h"
@@ -26,7 +27,6 @@
 #include "ImfTiledMisc.h"
 
 #include <algorithm>
-#include <mutex>
 #include <vector>
 
 OPENEXR_IMF_INTERNAL_NAMESPACE_SOURCE_ENTER
@@ -62,9 +62,13 @@ struct TileProcess
     exr_chunk_info_t      cinfo;
     exr_decode_pipeline_t decoder;
 
-    std::shared_ptr<TileProcess> next;
+    TileProcess*          next;
 };
 
+#if ILMTHREAD_THREADING_ENABLED
+using TileProcessGroup = ILMTHREAD_NAMESPACE::ProcessGroup<TileProcess>;
+#endif
+
 } // empty namespace
 
 //
@@ -78,9 +82,6 @@ struct TiledInputFile::Data
     : _ctxt (ctxt)
     , partNumber (pN)
     , numThreads (nT)
-#if ILMTHREAD_THREADING_ENABLED
-    , _sem ((unsigned int)nT)
-#endif
     {}
 
     void initialize ()
@@ -131,54 +132,28 @@ struct TiledInputFile::Data
 
 #if ILMTHREAD_THREADING_ENABLED
     std::mutex _mx;
-    ILMTHREAD_NAMESPACE::Semaphore _sem;
-#endif
-
-    std::shared_ptr<TileProcess> processStack;
-    std::shared_ptr<TileProcess> getChunkProcess ()
-    {
-        std::shared_ptr<TileProcess> retval;
-#if ILMTHREAD_THREADING_ENABLED
-        std::lock_guard<std::mutex> lk (_mx);
-#endif
-        retval = processStack;
-        if (!retval)
-            retval = std::make_shared<TileProcess> ();
-        processStack = retval->next;
-        retval->next.reset();
-        return retval;
-    }
-    void putChunkProcess (std::shared_ptr<TileProcess> tp)
-    {
-#if ILMTHREAD_THREADING_ENABLED
-        std::lock_guard<std::mutex> lk (_mx);
-#endif
-        tp->next = processStack;
-        processStack = tp;
-    }
 
-#if ILMTHREAD_THREADING_ENABLED
     class TileBufferTask final : public ILMTHREAD_NAMESPACE::Task
     {
     public:
         TileBufferTask (
             ILMTHREAD_NAMESPACE::TaskGroup* group,
             Data*                   ifd,
+            TileProcessGroup*       tileg,
             const FrameBuffer*      outfb,
             const exr_chunk_info_t& cinfo)
             : Task (group)
             , _outfb (outfb)
             , _ifd (ifd)
-            , _tile (ifd->getChunkProcess ())
+            , _tile (tileg->pop ())
+            , _tile_group (tileg)
         {
             _tile->cinfo = cinfo;
         }
 
         ~TileBufferTask () override
         {
-            if (_tile)
-                _ifd->putChunkProcess (std::move (_tile));
-            _ifd->_sem.post ();
+            _tile_group->push (_tile);
         }
 
         void execute () override;
@@ -189,7 +164,8 @@ struct TiledInputFile::Data
         const FrameBuffer* _outfb;
         Data*              _ifd;
 
-        std::shared_ptr<TileProcess> _tile;
+        TileProcess*       _tile;
+        TileProcessGroup*  _tile_group;
     };
 #endif
 };
@@ -296,7 +272,6 @@ TiledInputFile::setFrameBuffer (const FrameBuffer& frameBuffer)
     }
 
     _data->frameBuffer = frameBuffer;
-    _data->processStack.reset();
 }
 
 const FrameBuffer&
@@ -792,36 +767,43 @@ void TiledInputFile::Data::readTiles (int dx1, int dx2, int dy1, int dy2, int lx
 #if ILMTHREAD_THREADING_ENABLED
     if (nTiles > 1 && numThreads > 1)
     {
-        ILMTHREAD_NAMESPACE::TaskGroup tg;
+        // we need the lifetime of this to last longer than the
+        // lifetime of the task group below such that we don't get use
+        // after free type error, so use scope rules to accomplish
+        // this
+        TileProcessGroup tpg (numThreads);
 
-        for (int ty = dy1; ty <= dy2; ++ty)
         {
-            for (int tx = dx1; tx <= dx2; ++tx)
+            ILMTHREAD_NAMESPACE::TaskGroup tg;
+
+            for (int ty = dy1; ty <= dy2; ++ty)
             {
-                exr_result_t rv = exr_read_tile_chunk_info (
-                    *_ctxt, partNumber, tx, ty, lx, ly, &cinfo);
-                if (EXR_ERR_INCOMPLETE_CHUNK_TABLE == rv)
+                for (int tx = dx1; tx <= dx2; ++tx)
                 {
-                    THROW (
-                        IEX_NAMESPACE::InputExc,
-                        "Tile (" << tx << ", " << ty << ", " << lx << ", " << ly
-                        << ") is missing.");
-                }
-                else if (EXR_ERR_SUCCESS != rv)
-                    throw IEX_NAMESPACE::InputExc ("Unable to query tile information");
-
-                // used for honoring the numThreads
-                _sem.wait ();
+                    exr_result_t rv = exr_read_tile_chunk_info (
+                        *_ctxt, partNumber, tx, ty, lx, ly, &cinfo);
+                    if (EXR_ERR_INCOMPLETE_CHUNK_TABLE == rv)
+                    {
+                        THROW (
+                            IEX_NAMESPACE::InputExc,
+                            "Tile (" << tx << ", " << ty << ", " << lx << ", " << ly
+                            << ") is missing.");
+                    }
+                    else if (EXR_ERR_SUCCESS != rv)
+                        throw IEX_NAMESPACE::InputExc ("Unable to query tile information");
 
-                ILMTHREAD_NAMESPACE::ThreadPool::addGlobalTask (
-                    new TileBufferTask (&tg, this, &frameBuffer, cinfo) );
+                    ILMTHREAD_NAMESPACE::ThreadPool::addGlobalTask (
+                        new TileBufferTask (&tg, this, &tpg, &frameBuffer, cinfo) );
+                }
             }
         }
+
+        tpg.throw_on_failure ();
     }
     else
 #endif
     {
-        auto tp = getChunkProcess ();
+        TileProcess tp;
 
         for (int ty = dy1; ty <= dy2; ++ty)
         {
@@ -839,23 +821,14 @@ void TiledInputFile::Data::readTiles (int dx1, int dx2, int dy1, int dy2, int lx
                 else if (EXR_ERR_SUCCESS != rv)
                     throw IEX_NAMESPACE::InputExc ("Unable to query tile information");
 
-                tp->cinfo = cinfo;
-                tp->run_decode (
+                tp.cinfo = cinfo;
+                tp.run_decode (
                     *_ctxt,
                     partNumber,
                     &frameBuffer,
                     fill_list);
             }
         }
-
-        putChunkProcess (std::move(tp));
-    }
-
-    if (! _failures.empty())
-    {
-        std::string fail = _failures[0];
-        _failures.clear ();
-        throw IEX_NAMESPACE::IoExc (fail);
     }
 }
 
@@ -874,8 +847,11 @@ void TiledInputFile::Data::TileBufferTask::execute ()
     }
     catch (std::exception &e)
     {
-        std::lock_guard<std::mutex> lock (_ifd->_mx);
-        _ifd->_failures.emplace_back (std::string (e.what()));
+        _tile_group->record_failure (e.what ());
+    }
+    catch (...)
+    {
+        _tile_group->record_failure ("Unknown exception");
     }
 }
 #endif