Fix race around reference-capture in matmul example introduced with #60

examples/matmul/matmul.cc

@@ -60,31 +60,18 @@ void multiply(celerity::distr_queue queue, celerity::buffer<T, 2> mat_a, celerit
 	});
 }
 
-int main(int argc, char* argv[]) {
-	bool verification_passed = true;
-
-	celerity::distr_queue queue;
-
-	auto range = celerity::range<2>(MAT_SIZE, MAT_SIZE);
-	celerity::buffer<float, 2> mat_a_buf(range);
-	celerity::buffer<float, 2> mat_b_buf(range);
-	celerity::buffer<float, 2> mat_c_buf(range);
-
-	set_identity(queue, mat_a_buf);
-	set_identity(queue, mat_b_buf);
-
-	multiply(queue, mat_a_buf, mat_b_buf, mat_c_buf);
-	multiply(queue, mat_b_buf, mat_c_buf, mat_a_buf);
-
-	queue.submit(celerity::allow_by_ref, [&](celerity::handler& cgh) {
+template <typename T>
+void verify(celerity::distr_queue queue, celerity::buffer<T, 2> mat_a_buf, bool& verification_passed) {
+	// allow_by_ref is safe here as long as the caller of verify() ensures that verification_passed lives until the next synchronization point
+	queue.submit(celerity::allow_by_ref, [=, &verification_passed](celerity::handler& cgh) {
 		celerity::accessor result{mat_a_buf, cgh, celerity::access::one_to_one{}, celerity::read_only_host_task};
 
-		cgh.host_task(range, [=, &verification_passed](celerity::partition<2> part) {
+		cgh.host_task(mat_a_buf.get_range(), [=, &verification_passed](celerity::partition<2> part) {
 			auto sr = part.get_subrange();
 			for(size_t i = sr.offset[0]; i < sr.offset[0] + sr.range[0]; ++i) {
 				for(size_t j = sr.offset[0]; j < sr.offset[0] + sr.range[0]; ++j) {
 					const float received = result[{i, j}];
-					const float expected = float(i == j);
+					const float expected = i == j;
 					if(expected != received) {
 						fprintf(stderr, "VERIFICATION FAILED for element %zu,%zu: %f (received) != %f (expected)\n", i, j, received, expected);
 						verification_passed = false;
@@ -96,6 +83,25 @@ int main(int argc, char* argv[]) {
 			if(verification_passed) { printf("VERIFICATION PASSED!\n"); }
 		});
 	});
+}
+
+int main() {
+	celerity::distr_queue queue;
+
+	const auto range = celerity::range<2>(MAT_SIZE, MAT_SIZE);
+	celerity::buffer<float, 2> mat_a_buf(range);
+	celerity::buffer<float, 2> mat_b_buf(range);
+	celerity::buffer<float, 2> mat_c_buf(range);
+
+	set_identity(queue, mat_a_buf);
+	set_identity(queue, mat_b_buf);
+
+	multiply(queue, mat_a_buf, mat_b_buf, mat_c_buf);
+	multiply(queue, mat_b_buf, mat_c_buf, mat_a_buf);
+
+	bool verification_passed = true;
+	verify(queue, mat_a_buf, verification_passed);
+	queue.slow_full_sync(); // Wait for verification_passed to become available
 
 	return verification_passed ? EXIT_SUCCESS : EXIT_FAILURE;
 }