From 0a59e69fd922b02d9e3b5b043ee7f891061df7be Mon Sep 17 00:00:00 2001
From: Matthew Bentham <Matthew.Bentham@arm.com>
Date: Wed, 19 Jul 2023 15:01:00 +0000
Subject: Fix problem with exception handling in CPPScheduler

If an exception was thrown in the main thread, the child threads
were not being synchronised, leading to undefined behaviour (and
probably the program crashing instead of correctly propagating the
exception).

Add support to the build system for enabling ThreadSanitizer.
This needs a build system option rather than simply passing
extra_cxx/link_flags because the sanitizer options are
incompatible with -Wl,-undefined,error.

Add a unit test for throwing an exception within a CPPScheduler
workload.

Signed-off-by: Matthew Bentham <Matthew.Bentham@arm.com>
Change-Id: I7638272a5d43a24a861f3e6d63f3ee7b099483b5
Reviewed-on: https://eu-gerrit-1.euhpc.arm.com/c/VisualCompute/ComputeLibrary/+/538048
Comments-Addressed: bsgcomp <bsgcomp@arm.com>
Tested-by: bsgcomp <bsgcomp@arm.com>
Reviewed-by: Viet-Hoa Do <viet-hoa.do@arm.com>
Reviewed-on: https://review.mlplatform.org/c/ml/ComputeLibrary/+/9957
Tested-by: Arm Jenkins <bsgcomp@arm.com>
Comments-Addressed: Arm Jenkins <bsgcomp@arm.com>
Benchmark: Arm Jenkins <bsgcomp@arm.com>
---
 src/runtime/CPP/CPPScheduler.cpp | 35 +++++++++++++++++++++++++----------
 1 file changed, 25 insertions(+), 10 deletions(-)

(limited to 'src/runtime')

diff --git a/src/runtime/CPP/CPPScheduler.cpp b/src/runtime/CPP/CPPScheduler.cpp
index 39811ec156..45e872428f 100644
--- a/src/runtime/CPP/CPPScheduler.cpp
+++ b/src/runtime/CPP/CPPScheduler.cpp
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2016-2022 Arm Limited.
+ * Copyright (c) 2016-2023 Arm Limited.
  *
  * SPDX-License-Identifier: MIT
  *
@@ -172,7 +172,7 @@ public:
     void start();
 
     /** Wait for the current kernel execution to complete. */
-    void wait();
+    std::exception_ptr wait();
 
     /** Function ran by the worker thread. */
     void worker_thread();
@@ -244,17 +244,13 @@ void Thread::start()
     _cv.notify_one();
 }
 
-void Thread::wait()
+std::exception_ptr Thread::wait()
 {
     {
         std::unique_lock<std::mutex> lock(_m);
         _cv.wait(lock, [&] { return _job_complete; });
     }
-
-    if(_current_exception)
-    {
-        std::rethrow_exception(_current_exception);
-    }
+    return _current_exception;
 }
 
 void Thread::worker_thread()
@@ -509,15 +505,34 @@ void CPPScheduler::run_workloads(std::vector<IScheduler::Workload> &workloads)
         thread_it->start();
     }
     info.thread_id = t;                         // Set main thread's thread_id
-    process_workloads(workloads, feeder, info); // Main thread processes workloads
+    std::exception_ptr last_exception = nullptr;
 #ifndef ARM_COMPUTE_EXCEPTIONS_DISABLED
+    try
+    {
+#endif /* ARM_COMPUTE_EXCEPTIONS_DISABLED */
+        process_workloads(workloads, feeder, info); // Main thread processes workloads
+#ifndef ARM_COMPUTE_EXCEPTIONS_DISABLED
+    }
+    catch (...)
+    {
+        last_exception = std::current_exception();
+    }
+
     try
     {
 #endif /* ARM_COMPUTE_EXCEPTIONS_DISABLED */
         thread_it = _impl->_threads.begin();
         for(unsigned int i = 0; i < num_threads_to_use - 1; ++i, ++thread_it)
         {
-            thread_it->wait();
+            std::exception_ptr current_exception = thread_it->wait();
+            if (current_exception)
+            {
+                last_exception = current_exception;
+            }
+        }
+        if (last_exception)
+        {
+            std::rethrow_exception(last_exception);
         }
 #ifndef ARM_COMPUTE_EXCEPTIONS_DISABLED
     }
-- 
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