Added a test of Arena dependencies and destruction when using the new…

… aligned buffer feature.

fdbserver/VersionedBTree.actor.cpp

@@ -7820,6 +7820,27 @@ TEST_CASE(":/redwood/performance/mutationBuffer") {
 	return Void();
 }
 
+// This test is only useful with Arena debug statements which show when aligned buffers are allocated and freed.
+TEST_CASE(":/redwood/pager/ArenaPage") {
+	Arena x;
+	printf("Making p\n");
+	Reference<ArenaPage> p(new ArenaPage(4096, 4096));
+	printf("Made p=%p\n", p->begin());
+	printf("Clearing p\n");
+	p.clear();
+	printf("Making p\n");
+	p = Reference<ArenaPage>(new ArenaPage(4096, 4096));
+	printf("Made p=%p\n", p->begin());
+	printf("Making x depend on p\n");
+	x.dependsOn(p->getArena());
+	printf("Clearing p\n");
+	p.clear();
+	printf("Clearing x\n");
+	x = Arena();
+	printf("Pointer should be freed\n");
+	return Void();
+}
+
 TEST_CASE("/redwood/correctness/btree") {
 	g_redwoodMetricsActor = Void(); // Prevent trace event metrics from starting
 	g_redwoodMetrics.clear();

flow/Arena.cpp

@@ -239,6 +239,7 @@ void* ArenaBlock::makeAlignedBuffer(size_t alignment, size_t size) {
 	makeDefined(r, sizeof(ArenaBlockRef));
 	r->alignedBufferSize = size;
 	r->alignedBuffer = aligned_alloc(alignment, size);
+	// printf("Arena::alignedBuffer alloc %p\n", r->alignedBuffer);
 	r->nextBlockOffset = nextBlockOffset;
 	makeNoAccess(r, sizeof(ArenaBlockRef));
 	nextBlockOffset = bigUsed;
@@ -397,6 +398,7 @@ void ArenaBlock::destroy() {
 
 				// If alignedBuffer is valid, free it
 				if (br->alignedBufferSize != 0) {
+					// printf("Arena::alignedBuffer free %p\n", br->alignedBuffer);
 					aligned_free(br->alignedBuffer);
 				} else {
 					allowAccess(br->next);