python accessing freed shared memory object (#1253)

* added a 'isValid' member in shared memory (also updated shm version) with default true, any access to shared memory() checks also for validity. any free will set this to false and then unmap shm. Any access to shm will then check validity in python.

* fixed tests for shm

* added tests in python as well

---------

Co-authored-by: Alice <alice.mazzoleni@psi.ch>

slsDetectorSoftware/src/SharedMemory.h

@@ -10,6 +10,7 @@
  *@short functions basic implemenation of shared memory
  */
 
+#include "sls/TypeTraits.h"
 #include "sls/logger.h"
 #include "sls/sls_detector_exceptions.h"
 
@@ -26,11 +27,18 @@
 
 namespace sls {
 
+struct sharedDetector;
+
 #define SHM_DETECTOR_PREFIX "/slsDetectorPackage_detector_"
 #define SHM_MODULE_PREFIX   "_module_"
 #define SHM_ENV_NAME        "SLSDETNAME"
 
 template <typename T> class SharedMemory {
+
+    static_assert(has_bool_isValid<T>::value,
+                  "SharedMemory requires the struct to have a bool member "
+                  "named 'isValid'");
+
     static constexpr int NAME_MAX_LENGTH = 255;
     std::string name;
     T *shared_struct{nullptr};
@@ -65,15 +73,21 @@ template <typename T> class SharedMemory {
     }
 
     T *operator()() {
-        if (shared_struct)
-            return shared_struct;
-        throw SharedMemoryError(getNoShmAccessMessage());
+        if (!shared_struct)
+            throw SharedMemoryError(getNoShmAccessMessage());
+        if (!shared_struct->isValid) {
+            throw SharedMemoryError(getInvalidShmMessage());
+        }
+        return shared_struct;
     }
 
     const T *operator()() const {
-        if (shared_struct)
-            return shared_struct;
-        throw SharedMemoryError(getNoShmAccessMessage());
+        if (!shared_struct)
+            throw SharedMemoryError(getNoShmAccessMessage());
+        if (!shared_struct->isValid) {
+            throw SharedMemoryError(getInvalidShmMessage());
+        }
+        return shared_struct;
     }
 
     std::string getName() const { return name; }
@@ -215,10 +229,15 @@ template <typename T> class SharedMemory {
         }
     }
 
-    const char *getNoShmAccessMessage() const {
+    inline const char *getNoShmAccessMessage() const {
         return ("No shared memory to access. Create it first with "
                 "hostname or config command.");
     };
+
+    inline const char *getInvalidShmMessage() const {
+        return ("Shared memory is invalid or freed. Close resources before "
+                "access.");
+    };
 };
 
 } // namespace sls