le_safeRef.h

    1 /**
    2  * @page c_safeRef Safe References API
    3  *
    4  * @ref le_safeRef.h "API Reference"
    5  *
    6  * <HR>
    7  *
    8  *
    9  * The term "reference" is used to mean "opaque data that refers to some conceptual object".
   10  * It is intentionally vague to support "information hiding".  Behind the
   11  * scenes, different implementations can use almost anything that fits into a pointer as a
   12  * "reference".  Often, they are indexes into arrays or actual pointers to memory objects.
   13  * When passing those references through an API to outside clients, the implementation
   14  * becomes exposed to crash bugs when clients
   15  * pass those references back into the API damaged or stale ("stale" meaning
   16  * something that has been deleted).
   17  *
   18  * <b> Safe References </b> are designed to help protect against damaged or stale references being
   19  * used by clients.
   20  *
   21  * @section c_safeRef_create Create Safe Reference
   22  *
   23  * Client calls an API's "Create" function:
   24  *  - "Create" function creates an object.
   25  *  - "Create" function creates a "Safe Reference" for the new object @c le_ref_CreateRef()
   26  *  - "Create" function returns the Safe Reference.
   27  *
   28  * @section c_safeRef_lookup Lookup Pointer
   29  *
   30  * Followed by:
   31  *
   32  * Client calls another API function, passing in the Safe Reference:
   33  *  - API function translates the Safe Reference back into an object pointer @c le_ref_Lookup()
   34  *  - API function acts on the object.
   35  *
   36  * @section c_safeRef_delete Delete Safe Reference
   37  *
   38  * Finishing with:
   39  *
   40  * Client calls API's "Delete" function, passing in the Safe Reference:
   41  *  - "Delete" function translates the Safe Reference back into a pointer to its object.
   42  *  - "Delete" function invalidates the Safe Reference @c le_ref_DeleteRef()
   43  *  - "Delete" function deletes the object.
   44  *
   45  * At this point, if the Client calls an API function and passes that same (now invalid) Safe Reference
   46  * (or if the client accidentally passes in some garbage value, like a pointer or zero), the
   47  * API function will try to translate that into an object pointer. But it'll be told that it's
   48  * an invalid Safe Reference. The API function can then handle it gracefully, rather
   49  * than just acting as if it were a valid reference and clobbering the object's deallocated
   50  * memory or some other object that's reusing the old object's memory.
   51  *
   52  * @section c_safeRef_map Create Referece Map
   53  *
   54  * A <b> Reference Map </b> object can be used to create Safe References and keep track of the
   55  * mappings from Safe References to pointers.  At start-up, a Reference Map is
   56  * created by calling @c le_ref_CreateMap().  It takes a single argument, the maximum number
   57  * of mappings expected to track of at any time.
   58  *
   59  * @section c_safeRef_multithreading Multithreading
   60  *
   61  * This API's functions are reentrant, but not thread safe. If there's the slightest
   62  * possibility the same Reference Map will be accessed by two threads at the same time, use
   63  * a mutex or some other thread synchronization mechanism to protect the Reference Map from
   64  * concurrent access.
   65  *
   66  * @section c_safeRef_example Sample Code
   67  *
   68  * Here's an API Definition sample:
   69  *
   70  * @code
   71  * // Opaque reference to Foo objects.
   72  * typedef struct xyz_foo_Obj* xyz_foo_ObjRef_t;
   73  *
   74  * xyz_foo_Ref_t xyz_foo_CreateObject
   75  * (
   76  *     void
   77  * );
   78  *
   79  * void xyz_foo_DoSomething
   80  * (
   81  *     xyz_foo_Ref_t objRef
   82  * );
   83  *
   84  * void xyz_foo_DeleteObject
   85  * (
   86  *     xyz_foo_Ref_t objRef
   87  * );
   88  * @endcode
   89  *
   90  * Here's an API Implementation sample:
   91  *
   92  * @code
   93  * // Maximum number of Foo objects we expect to have at one time.
   94  * #define MAX_FOO_OBJECTS  27
   95  *
   96  * // Actual Foo objects.
   97  * typedef struct
   98  * {
   99  *     ...
  100  * }
  101  * Foo_t;
  102  *
  103  * // Pool from which Foo objects are allocated.
  104  * le_mem_PoolRef_t FooPool;
  105  *
  106  * // Safe Reference Map for Foo objects.
  107  * le_ref_MapRef_t FooRefMap;
  108  *
  109  * COMPONENT_INIT
  110  * {
  111  *     // Create the Foo object pool.
  112  *     FooPool = le_mem_CreatePool("FooPool", sizeof(Foo_t));
  113  *     le_mem_ExpandPool(FooPool, MAX_FOO_OBJECTS);
  114  *
  115  *     // Create the Safe Reference Map to use for Foo object Safe References.
  116  *     FooRefMap = le_ref_CreateMap("FooMap", MAX_FOO_OBJECTS);
  117  * };
  118  *
  119  * xyz_foo_Ref_t xyz_foo_CreateObject
  120  * (
  121  *     void
  122  * )
  123  * {
  124  *     Foo_t* fooPtr = le_mem_ForceAlloc(FooPool);
  125  *
  126  *     // Initialize the new Foo object.
  127  *     ...
  128  *
  129  *     // Create and return a Safe Reference for this Foo object.
  130  *     return le_ref_CreateRef(FooRefMap, fooPtr);
  131  * }
  132  *
  133  * void xyz_foo_DoSomething
  134  * (
  135  *     xyz_foo_Ref_t objRef
  136  * )
  137  * {
  138  *     Foo_t* fooPtr = le_ref_Lookup(FooRefMap, objRef);
  139  *
  140  *     if (fooPtr == NULL)
  141  *     {
  142  *         LE_CRIT("Invalid reference (%p) provided!", objRef);
  143  *         return;
  144  *     }
  145  *
  146  *     // Do something to the object.
  147  *     ...
  148  * }
  149  *
  150  * void xyz_foo_DeleteObject
  151  * (
  152  *     xyz_foo_Ref_t objRef
  153  * )
  154  * {
  155  *     Foo_t* fooPtr = le_ref_Lookup(FooRefMap, objRef);
  156  *
  157  *     if (fooPtr == NULL)
  158  *     {
  159  *         LE_CRIT("Invalid reference (%p) provided!", objRef);
  160  *         return;
  161  *     }
  162  *
  163  *     // Invalidate the Safe Reference.
  164  *     le_ref_DeleteRef(FooRefMap, objRef);
  165  *
  166  *     // Release the Foo object.
  167  *     le_mem_Release(fooPtr);
  168  * }
  169  * @endcode
  170  *
  171  * <HR>
  172  *
  173  * Copyright (C) Sierra Wireless Inc. Use of this work is subject to license.
  174  */
  175 
  176 /** @file le_safeRef.h
  177  *
  178  * Legato @ref c_safeRef include file.
  179  *
  180  * Copyright (C) Sierra Wireless Inc. Use of this work is subject to license.
  181  */
  182 
  183 #ifndef LEGATO_SAFEREF_INCLUDE_GUARD
  184 #define LEGATO_SAFEREF_INCLUDE_GUARD
  185 
  186 //--------------------------------------------------------------------------------------------------
  187 /**
  188  * Reference to a "Reference Map" object, which stores mappings from Safe References to pointers.
  189  */
  190 //--------------------------------------------------------------------------------------------------
  191 typedef struct le_ref_Map* le_ref_MapRef_t;
  192 
  193 
  194 //--------------------------------------------------------------------------------------------------
  195 /**
  196  * Reference to an "iterator" object, used to manage iterating a collection of safe refs.
  197  */
  198 //--------------------------------------------------------------------------------------------------
  199 typedef struct le_ref_Iter* le_ref_IterRef_t;
  200 
  201 
  202 //--------------------------------------------------------------------------------------------------
  203 /**
  204  * Create a Reference Map that can hold mappings from Safe References to pointers.
  205  *
  206  * @return A reference to the Reference Map object.
  207  */
  208 //--------------------------------------------------------------------------------------------------
  209 le_ref_MapRef_t le_ref_CreateMap
  210 (
  211     const char* name,   ///< [in] Name of the map (for diagnostics).
  212 
  213     size_t      maxRefs ///< [in] Maximum number of Safe References expected to be kept in
  214                         ///       this Reference Map at any one time.
  215 );
  216 
  217 
  218 //--------------------------------------------------------------------------------------------------
  219 /**
  220  * Creates a Safe Reference, storing a mapping between that reference and a specified pointer for
  221  * future lookup.
  222  *
  223  * @return The Safe Reference.
  224  */
  225 //--------------------------------------------------------------------------------------------------
  226 void* le_ref_CreateRef
  227 (
  228     le_ref_MapRef_t mapRef, ///< [in] Reference Map in which the mapping should be kept.
  229     void*           ptr     ///< [in] Pointer value to which the new Safe Reference will be mapped.
  230 );
  231 
  232 
  233 //--------------------------------------------------------------------------------------------------
  234 /**
  235  * Translates a Safe Reference back to the pointer from when the Safe Reference
  236  * was created.
  237  *
  238  * @return Pointer that the Safe Reference maps to, or NULL if the Safe Reference has been
  239  *         deleted or is invalid.
  240  */
  241 //--------------------------------------------------------------------------------------------------
  242 void* le_ref_Lookup
  243 (
  244     le_ref_MapRef_t mapRef, ///< [in] Reference Map to do the lookup in.
  245     void*           safeRef ///< [in] Safe Reference to be translated into a pointer.
  246 );
  247 
  248 
  249 //--------------------------------------------------------------------------------------------------
  250 /**
  251  * Deletes a Safe Reference.
  252  */
  253 //--------------------------------------------------------------------------------------------------
  254 void le_ref_DeleteRef
  255 (
  256     le_ref_MapRef_t mapRef, ///< [in] Reference Map to delete the mapping from.
  257     void*           safeRef ///< [in] Safe Reference to be deleted (invalidated).
  258 );
  259 
  260 
  261 //--------------------------------------------------------------------------------------------------
  262 /**
  263  * Gets an interator for step-by-step iteration over the map. In this mode the iteration is
  264  * controlled by the calling function using the le_ref_NextNode() function.  There is one iterator
  265  * per map, and calling this function resets the iterator position to the start of the map.  The
  266  * iterator is not ready for data access until le_ref_NextNode() has been called at least once.
  267  *
  268  * @return  Returns A reference to a hashmap iterator which is ready for le_hashmap_NextNode() to be
  269  *          called on it.
  270  */
  271 //--------------------------------------------------------------------------------------------------
  272 le_ref_IterRef_t le_ref_GetIterator
  273 (
  274     le_ref_MapRef_t mapRef ///< [in] Reference to the map.
  275 );
  276 
  277 
  278 //--------------------------------------------------------------------------------------------------
  279 /**
  280  * Moves the iterator to the next key/value pair in the map.
  281  *
  282  * @return  Returns LE_OK unless you go past the end of the map, then returns LE_NOT_FOUND.
  283  *          If the iterator has been invalidated by the map changing or you have previously
  284  *          received a LE_NOT_FOUND then this returns LE_FAULT.
  285  */
  286 //--------------------------------------------------------------------------------------------------
  287 le_result_t le_ref_NextNode
  288 (
  289     le_ref_IterRef_t iteratorRef ///< [IN] Reference to the iterator.
  290 );
  291 
  292 
  293 //--------------------------------------------------------------------------------------------------
  294 /**
  295  * Retrieves a pointer to the safe ref iterator is currently pointing at.  If the iterator has just
  296  * been initialized and le_hashmap_NextNode() has not been called, or if the iterator has been
  297  * invalidated then this will return NULL.
  298  *
  299  * @return  A pointer to the current key, or NULL if the iterator has been invalidated or is not ready.
  300  *
  301  */
  302 //--------------------------------------------------------------------------------------------------
  303 void const * le_ref_GetSafeRef
  304 (
  305     le_ref_IterRef_t iteratorRef ///< [IN] Reference to the iterator.
  306 );
  307 
  308 
  309 //--------------------------------------------------------------------------------------------------
  310 /**
  311  * Retrieves a pointer to the value which the iterator is currently pointing at.  If the iterator
  312  * has just been initialized and le_ref_NextNode() has not been called, or if the iterator has been
  313  * invalidated then this will return NULL.
  314  *
  315  * @return  A pointer to the current value, or NULL if the iterator has been invalidated or is not
  316  *          ready.
  317  */
  318 //--------------------------------------------------------------------------------------------------
  319 void const * le_ref_GetValue
  320 (
  321     le_ref_IterRef_t iteratorRef ///< [IN] Reference to the iterator.
  322 );
  323 
  324 
  325 #endif // LEGATO_SAFEREF_INCLUDE_GUARD
le_result_t
le_result_t
Definition: le_basics.h:35
le_ref_IterRef_t
struct le_ref_Iter * le_ref_IterRef_t
Definition: le_safeRef.h:199
le_ref_MapRef_t
struct le_ref_Map * le_ref_MapRef_t
Definition: le_safeRef.h:191
le_ref_CreateMap
le_ref_MapRef_t le_ref_CreateMap(const char *name, size_t maxRefs)
le_ref_GetIterator
le_ref_IterRef_t le_ref_GetIterator(le_ref_MapRef_t mapRef)
le_ref_DeleteRef
void le_ref_DeleteRef(le_ref_MapRef_t mapRef, void *safeRef)
le_ref_CreateRef
void * le_ref_CreateRef(le_ref_MapRef_t mapRef, void *ptr)
le_ref_NextNode
le_result_t le_ref_NextNode(le_ref_IterRef_t iteratorRef)
le_ref_GetSafeRef
void const * le_ref_GetSafeRef(le_ref_IterRef_t iteratorRef)
le_ref_Lookup
void * le_ref_Lookup(le_ref_MapRef_t mapRef, void *safeRef)
le_ref_GetValue
void const * le_ref_GetValue(le_ref_IterRef_t iteratorRef)