From 5c8c3ae3f3012b5c95e8ec124bfbf7094dcadc51 Mon Sep 17 00:00:00 2001
From: Dhanya Thattil <33750417+thattil@users.noreply.github.com>
Date: Mon, 13 Feb 2023 11:29:54 +0100
Subject: [PATCH] fix to access to shared memory that doesnt exist (#638)

* fix to access to shared memory that doesnt exist

* fix for freeing shm and then setting hostname from API

* exception error message moved to private function

* refactoring to avoid allocating intermediate string
---
 slsDetectorSoftware/src/DetectorImpl.cpp |  9 +++++----
 slsDetectorSoftware/src/SharedMemory.h   | 21 ++++++++++++++++++---
 2 files changed, 23 insertions(+), 7 deletions(-)

diff --git a/slsDetectorSoftware/src/DetectorImpl.cpp b/slsDetectorSoftware/src/DetectorImpl.cpp
index d75edce8e..ed1d07622 100644
--- a/slsDetectorSoftware/src/DetectorImpl.cpp
+++ b/slsDetectorSoftware/src/DetectorImpl.cpp
@@ -253,14 +253,15 @@ void DetectorImpl::setVirtualDetectorServers(const int numdet, const int port) {
 }
 
 void DetectorImpl::setHostname(const std::vector<std::string> &name) {
-    // this check is there only to allow the previous detsizechan command
-    if (shm()->totalNumberOfModules != 0) {
+    // do not free always to allow the previous detsize/ initialchecks command
+    if (shm.exists() && shm()->totalNumberOfModules != 0) {
         LOG(logWARNING) << "There are already module(s) in shared memory."
                            "Freeing Shared memory now.";
-        bool initialChecks = shm()->initialChecks;
         freeSharedMemory();
+    }
+    // could be called after freeing shm from API
+    if (!shm.exists()) {
         setupDetector();
-        shm()->initialChecks = initialChecks;
     }
     for (const auto &hostname : name) {
         addModule(hostname);
diff --git a/slsDetectorSoftware/src/SharedMemory.h b/slsDetectorSoftware/src/SharedMemory.h
index e31fc5fb9..a8e436664 100644
--- a/slsDetectorSoftware/src/SharedMemory.h
+++ b/slsDetectorSoftware/src/SharedMemory.h
@@ -33,7 +33,7 @@ namespace sls {
 template <typename T> class SharedMemory {
     static constexpr int NAME_MAX_LENGTH = 255;
     std::string name;
-    T *shared_struct{};
+    T *shared_struct{nullptr};
 
   public:
     // moduleid of -1 creates a detector only shared memory
@@ -64,8 +64,18 @@ template <typename T> class SharedMemory {
             unmapSharedMemory();
     }
 
-    T *operator()() { return shared_struct; }
-    const T *operator()() const { return shared_struct; }
+    T *operator()() {
+        if (shared_struct)
+            return shared_struct;
+        throw SharedMemoryError(getNoShmAccessMessage());
+    }
+
+    const T *operator()() const {
+        if (shared_struct)
+            return shared_struct;
+        throw SharedMemoryError(getNoShmAccessMessage());
+    }
+
     std::string getName() const { return name; }
 
     bool exists() {
@@ -204,6 +214,11 @@ template <typename T> class SharedMemory {
             throw SharedMemoryError(msg);
         }
     }
+
+    const char* getNoShmAccessMessage() const {
+        return ("No shared memory to access. Create it first with "
+                           "hostname or config command.");
+    };
 };
 
 } // namespace sls