From 4f9c07b4faafbf6908806f222fe71ef00dec49f4 Mon Sep 17 00:00:00 2001
From: Filip Leonarski <filip.leonarski@psi.ch>
Date: Tue, 3 Mar 2026 20:54:15 +0100
Subject: [PATCH] ZeroCopyReturnValue: Reset status properly

---
 common/ZeroCopyReturnValue.cpp | 23 ++++-----
 tests/ImageBufferTest.cpp      | 90 ++++++++++++++++++++++++++++++++++
 2 files changed, 102 insertions(+), 11 deletions(-)

diff --git a/common/ZeroCopyReturnValue.cpp b/common/ZeroCopyReturnValue.cpp
index 0e6c5b69..984b9082 100644
--- a/common/ZeroCopyReturnValue.cpp
+++ b/common/ZeroCopyReturnValue.cpp
@@ -7,8 +7,8 @@
 #include "ThreadSafeFIFO.h"
 
 ZeroCopyReturnValue::ZeroCopyReturnValue(void *in_ptr, ImageBuffer &in_ctrl, uint32_t in_handle)
-: ptr(in_ptr), payload_size(0), image_number(-1), buf_ctrl(in_ctrl), handle(in_handle),
-indexed(false) {
+    : ptr(in_ptr), payload_size(0), image_number(-1), buf_ctrl(in_ctrl), handle(in_handle),
+      indexed(false) {
 }
 
 void ZeroCopyReturnValue::SetImageNumber(int64_t in_image_number) {
@@ -23,20 +23,21 @@ size_t ZeroCopyReturnValue::GetImageSize() const {
     return payload_size;
 }
 
-void * ZeroCopyReturnValue::GetImage() const {
+void *ZeroCopyReturnValue::GetImage() const {
     return ptr;
 }
 
 void ZeroCopyReturnValue::release() {
- if (status == ImageBufferEntryStatus::InPreparation)
-     ReadyToSend();
+    if (status == ImageBufferEntryStatus::InPreparation)
+        ReadyToSend();
 
-if (status == ImageBufferEntryStatus::Sending) {
-     buf_ctrl.ReleaseSlot(handle);
-} else {
-    throw JFJochException(JFJochExceptionCategory::InputParameterInvalid,
-                          "Trying to send image that is not in preparation");
-}
+    if (status == ImageBufferEntryStatus::Sending) {
+        buf_ctrl.ReleaseSlot(handle);
+        status = ImageBufferEntryStatus::InPreparation;
+    } else {
+        throw JFJochException(JFJochExceptionCategory::InputParameterInvalid,
+                              "Trying to send image that is not in preparation");
+    }
 }
 
 int64_t ZeroCopyReturnValue::GetImageNumber() const {
diff --git a/tests/ImageBufferTest.cpp b/tests/ImageBufferTest.cpp
index f1042dcd..977c5ad8 100644
--- a/tests/ImageBufferTest.cpp
+++ b/tests/ImageBufferTest.cpp
@@ -243,3 +243,93 @@ TEST_CASE("ImageBuffer_BuffersNotReturned") {
     REQUIRE(buf_ctrl.GetAvailSlots() == 3);
     REQUIRE(!buf_ctrl.CheckIfBufferReturned(std::chrono::microseconds(1)));
 }
+
+TEST_CASE("ImageBuffer_SlotReuse") {
+    DiffractionExperiment experiment(DetJF(18,3,8,36));
+
+    // Only 1 slot so reuse is guaranteed
+    ImageBuffer buf_ctrl(experiment.GetImageBufferLocationSize());
+    buf_ctrl.StartMeasurement(experiment);
+
+    REQUIRE(buf_ctrl.GetStatus().total_slots == 1);
+    REQUIRE(buf_ctrl.GetAvailSlots() == 1);
+
+    // First cycle: acquire -> ReadyToSend -> release
+    ZeroCopyReturnValue *ret = buf_ctrl.GetImageSlot();
+    REQUIRE(ret != nullptr);
+    REQUIRE(buf_ctrl.GetAvailSlots() == 0);
+
+    ret->SetImageNumber(0);
+    ret->SetImageSize(100);
+    ret->SetIndexed(false);
+    ret->ReadyToSend();
+
+    REQUIRE(buf_ctrl.GetStatus().sending_slots == 1);
+    REQUIRE(buf_ctrl.GetStatus().preparation_slots == 0);
+
+    ret->release();
+
+    REQUIRE(buf_ctrl.GetAvailSlots() == 1);
+    REQUIRE(buf_ctrl.GetStatus().sending_slots == 0);
+
+    // Second cycle: reuse the same slot — this is where the bug manifested
+    ZeroCopyReturnValue *ret2 = buf_ctrl.GetImageSlot();
+    REQUIRE(ret2 != nullptr);
+    REQUIRE(buf_ctrl.GetAvailSlots() == 0);
+    REQUIRE(buf_ctrl.GetStatus().preparation_slots == 1);
+
+    ret2->SetImageNumber(1);
+    ret2->SetImageSize(200);
+    ret2->SetIndexed(true);
+    REQUIRE_NOTHROW(ret2->ReadyToSend());
+
+    REQUIRE(buf_ctrl.GetStatus().sending_slots == 1);
+    REQUIRE(buf_ctrl.GetStatus().preparation_slots == 0);
+
+    REQUIRE_NOTHROW(ret2->release());
+
+    REQUIRE(buf_ctrl.GetAvailSlots() == 1);
+    REQUIRE(buf_ctrl.GetStatus().sending_slots == 0);
+
+    // Third cycle: verify it keeps working
+    ZeroCopyReturnValue *ret3 = buf_ctrl.GetImageSlot();
+    REQUIRE(ret3 != nullptr);
+
+    ret3->SetImageNumber(2);
+    ret3->SetImageSize(300);
+    ret3->SetIndexed(false);
+    REQUIRE_NOTHROW(ret3->ReadyToSend());
+    REQUIRE_NOTHROW(ret3->release());
+
+    REQUIRE(buf_ctrl.GetAvailSlots() == 1);
+    REQUIRE(buf_ctrl.Finalize(std::chrono::microseconds(1)));
+}
+
+TEST_CASE("ImageBuffer_SlotReuse_ReleaseFromInPreparation") {
+    DiffractionExperiment experiment(DetJF(18,3,8,36));
+
+    ImageBuffer buf_ctrl(experiment.GetImageBufferLocationSize());
+    buf_ctrl.StartMeasurement(experiment);
+
+    // First cycle: acquire -> release directly (skipping explicit ReadyToSend)
+    ZeroCopyReturnValue *ret = buf_ctrl.GetImageSlot();
+    REQUIRE(ret != nullptr);
+
+    ret->SetImageNumber(0);
+    ret->SetImageSize(100);
+    ret->release();
+
+    REQUIRE(buf_ctrl.GetAvailSlots() == 1);
+
+    // Second cycle: reuse after release-from-InPreparation path
+    ZeroCopyReturnValue *ret2 = buf_ctrl.GetImageSlot();
+    REQUIRE(ret2 != nullptr);
+
+    ret2->SetImageNumber(1);
+    ret2->SetImageSize(200);
+    REQUIRE_NOTHROW(ret2->ReadyToSend());
+    REQUIRE_NOTHROW(ret2->release());
+
+    REQUIRE(buf_ctrl.GetAvailSlots() == 1);
+    REQUIRE(buf_ctrl.Finalize(std::chrono::microseconds(1)));
+}
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