le_mutex.h

    1 /**
    2  * @page c_mutex Mutex API
    3  *
    4  * @subpage le_mutex.h "API Reference"
    5  *
    6  * <HR>
    7  *
    8  * The Mutex API provides standard mutex functionality with added diagnostics capabilities.
    9  * These mutexes can be shared by threads within the same process, but can't
   10  * be shared by threads in different processes.
   11  *
   12  * @warning  Multithreaded programming is an advanced subject with many pitfalls.
   13  * A general discussion of why and how mutexes are used in multithreaded programming is beyond
   14  * the scope of this documentation.  If you are not familiar with these concepts @e please seek
   15  * out training and mentorship before attempting to work on multithreaded production code.
   16  *
   17  * Two kinds of mutex are supported by Legato:
   18  *  - @b Recursive or
   19  *  - @b Non-Recursive
   20  *
   21  * All mutexes can be locked and unlocked. The same lock, unlock, and delete
   22  * functions work for all the mutexes, regardless of what type they are.
   23  *
   24  * A recursive mutex can be locked again by the same thread that already has the lock, but
   25  * a non-recursive mutex can only be locked once before being unlocked.
   26  *
   27  * If a thread grabs a non-recursive mutex lock and then tries to grab that same lock again, a
   28  * deadlock occurs.  Legato's non-recursive mutexes will detect this deadlock, log a fatal error
   29  * and terminate the process.
   30  *
   31  * If a thread grabs a recursive mutex, and then the same thread grabs the same lock again, the
   32  * mutex's "lock count" is incremented.  When the thread unlocks that mutex, the lock count is
   33  * decremented.  Only when the lock count reaches zero will the mutex actually unlock.
   34  *
   35  * There's a limit to the number of times the same recursive mutex can be locked by the same
   36  * thread without ever unlocking it, but that limit is so high (at least 2 billion), if that
   37  * much recursion is going on, there are other, more serious problems with the program.
   38  *
   39  * @section c_mutex_create Creating a Mutex
   40  *
   41  * In Legato, mutexes are dynamically allocated objects.  Functions that create them
   42  * return references to them (of type le_mutex_Ref_t).
   43  *
   44  * Functions for creating mutexes:
   45  *  - @c le_mutex_CreateRecursive() - creates a recursive mutex.
   46  *  - @c le_mutex_CreateNonRecursive() - creates a non-recursive mutex.
   47  *
   48  * All mutexes have names, required for diagnostic purposes.  See
   49  * @ref c_mutex_diagnostics below.
   50  *
   51  * @section c_mutex_locking Using a Mutex
   52  *
   53  * Functions for locking and unlocking mutexes:
   54  *  - @c le_mutex_Lock()
   55  *  - @c le_mutex_Unlock()
   56  *  - @c le_mutex_TryLock()
   57  *
   58  * It doesn't matter what type of mutex you are using, you
   59  * still use the same functions for locking and unlocking your mutex.
   60  *
   61  * @section c_mutex_delete Deleting a Mutex
   62  *
   63  * When you are finished with a mutex, you must delete it by calling le_mutex_Delete().
   64  *
   65  * There must not be anyone using the mutex when it is deleted (i.e., no one can be holding it).
   66  *
   67  * @section c_mutex_diagnostics Diagnostics
   68  *
   69  * The command-line diagnostic tool @ref toolsTarget_inspect can be used to list the mutexes
   70  * that currently exist inside a given process.  The state of each mutex can be
   71  * seen, including a list of any threads that might be waiting for that mutex.
   72  *
   73  * <HR>
   74  *
   75  * Copyright (C) Sierra Wireless Inc.
   76  */
   77 
   78 //--------------------------------------------------------------------------------------------------
   79 /**
   80  * @file le_mutex.h
   81  *
   82  * Legato @ref c_mutex include file.
   83  *
   84  * Copyright (C) Sierra Wireless Inc.
   85  */
   86 //--------------------------------------------------------------------------------------------------
   87 
   88 #ifndef LEGATO_MUTEX_INCLUDE_GUARD
   89 #define LEGATO_MUTEX_INCLUDE_GUARD
   90 
   91 //--------------------------------------------------------------------------------------------------
   92 /**
   93  * Reference to a Mutex object.
   94  */
   95 //--------------------------------------------------------------------------------------------------
   96 typedef struct le_mutex* le_mutex_Ref_t;
   97 
   98 
   99 #if LE_CONFIG_MUTEX_NAMES_ENABLED
  100 //--------------------------------------------------------------------------------------------------
  101 /**
  102  * Create a Recursive mutex.
  103  *
  104  *  @param[in]  nameStr Name of the mutex
  105  *
  106  *  @return  Returns a reference to the mutex.
  107  *
  108  *  @note Terminates the process on failure, no need to check the return value for errors.
  109  */
  110 //--------------------------------------------------------------------------------------------------
  111 le_mutex_Ref_t le_mutex_CreateRecursive
  112 (
  113     const char *nameStr
  114 );
  115 #else /* if not LE_CONFIG_MUTEX_NAMES_ENABLED */
  116 /// @cond HIDDEN_IN_USER_DOCS
  117 //--------------------------------------------------------------------------------------------------
  118 /**
  119  * Internal function used to implement le_mutex_CreateRecursive().
  120  */
  121 //--------------------------------------------------------------------------------------------------
  122 le_mutex_Ref_t _le_mutex_CreateRecursive(void);
  123 /// @endcond
  124 //--------------------------------------------------------------------------------------------------
  125 /**
  126  * Create a Recursive mutex.
  127  *
  128  *  @param[in]  nameStr Name of the mutex
  129  *
  130  *  @return  Returns a reference to the mutex.
  131  *
  132  *  @note Terminates the process on failure, no need to check the return value for errors.
  133  */
  134 //--------------------------------------------------------------------------------------------------
  135 LE_DECLARE_INLINE le_mutex_Ref_t le_mutex_CreateRecursive
  136 (
  137     const char *nameStr
  138 )
  139 {
  140     LE_UNUSED(nameStr);
  141     return _le_mutex_CreateRecursive();
  142 }
  143 #endif /* end LE_CONFIG_MUTEX_NAMES_ENABLED */
  144 
  145 
  146 #if LE_CONFIG_MUTEX_NAMES_ENABLED
  147 //--------------------------------------------------------------------------------------------------
  148 /**
  149  * Create a Non-Recursive mutex.
  150  *
  151  *  @param[in]  nameStr Name of the mutex
  152  *
  153  *  @return  Returns a reference to the mutex.
  154  *
  155  *  @note Terminates the process on failure, no need to check the return value for errors.
  156  */
  157 //--------------------------------------------------------------------------------------------------
  158 le_mutex_Ref_t le_mutex_CreateNonRecursive
  159 (
  160     const char *nameStr
  161 );
  162 #else /* if not LE_CONFIG_MUTEX_NAMES_ENABLED */
  163 /// @cond HIDDEN_IN_USER_DOCS
  164 //--------------------------------------------------------------------------------------------------
  165 /**
  166  * Internal function used to implement le_mutex_CreateNonRecursive().
  167  */
  168 //--------------------------------------------------------------------------------------------------
  169 le_mutex_Ref_t _le_mutex_CreateNonRecursive(void);
  170 /// @endcond
  171 //--------------------------------------------------------------------------------------------------
  172 /**
  173  * Create a Non-Recursive mutex.
  174  *
  175  *  @param[in]  nameStr Name of the mutex
  176  *
  177  *  @return  Returns a reference to the mutex.
  178  *
  179  *  @note Terminates the process on failure, no need to check the return value for errors.
  180  */
  181 //--------------------------------------------------------------------------------------------------
  182 LE_DECLARE_INLINE le_mutex_Ref_t le_mutex_CreateNonRecursive
  183 (
  184     const char *nameStr
  185 )
  186 {
  187     LE_UNUSED(nameStr);
  188     return _le_mutex_CreateNonRecursive();
  189 }
  190 #endif /* end LE_CONFIG_MUTEX_NAMES_ENABLED */
  191 
  192 
  193 //--------------------------------------------------------------------------------------------------
  194 /**
  195  * Delete a mutex.
  196  *
  197  * @return  Nothing.
  198  */
  199 //--------------------------------------------------------------------------------------------------
  200 void le_mutex_Delete
  201 (
  202     le_mutex_Ref_t    mutexRef   ///< [in] Mutex reference
  203 );
  204 
  205 //--------------------------------------------------------------------------------------------------
  206 /**
  207  * Lock a mutex.
  208  *
  209  * @return  Nothing.
  210  */
  211 //--------------------------------------------------------------------------------------------------
  212 void le_mutex_Lock
  213 (
  214     le_mutex_Ref_t    mutexRef   ///< [in] Mutex reference
  215 );
  216 
  217 //--------------------------------------------------------------------------------------------------
  218 /**
  219  * Try a lock on a mutex.
  220  *
  221  * Locks a mutex, if no other thread holds it.  Otherwise, returns without locking.
  222  *
  223  * @return
  224  *  - LE_OK if mutex was locked.
  225  *  - LE_WOULD_BLOCK if mutex was already held by someone else.
  226  */
  227 //--------------------------------------------------------------------------------------------------
  228 le_result_t le_mutex_TryLock
  229 (
  230     le_mutex_Ref_t    mutexRef   ///< [in] Mutex reference
  231 );
  232 
  233 //--------------------------------------------------------------------------------------------------
  234 /**
  235  * Unlock a mutex.
  236  *
  237  * @return  Nothing.
  238  */
  239 //--------------------------------------------------------------------------------------------------
  240 void le_mutex_Unlock
  241 (
  242     le_mutex_Ref_t    mutexRef   ///< [in] Mutex reference
  243 );
  244 
  245 //--------------------------------------------------------------------------------------------------
  246 /**
  247  * Declare a static mutex reference variable and accessor functions.
  248  *
  249  * This is handy when you need a single, file-scope mutex for use inside your module
  250  * to protect other file-scope data structures from multi-threaded race conditions.
  251  *
  252  * Adding the line
  253  * @code
  254  * LE_MUTEX_DECLARE_REF(MyMutexRef);
  255  * @endcode
  256  * near the top of your file will create a file-scope variable called "MyMutexRef" of type
  257  * le_mutex_Ref_t and functions called "Lock" and "Unlock" that access that variable.
  258  *
  259  * See @ref c_mutex_locking_tips for more information.
  260  *
  261  * @param   refName Name of the mutex reference variable.
  262  *
  263  * @return  Nothing.
  264  */
  265 //--------------------------------------------------------------------------------------------------
  266 #define LE_MUTEX_DECLARE_REF(refName) \
  267     static le_mutex_Ref_t refName; \
  268     static inline void Lock(void) { le_mutex_Lock(refName); } \
  269     static inline void Unlock(void) { le_mutex_Unlock(refName); }
  270 
  271 #endif /* LEGATO_MUTEX_INCLUDE_GUARD */
le_result_t
le_result_t
Definition: le_basics.h:46
LE_UNUSED
#define LE_UNUSED(v)
Definition: le_basics.h:369
le_mutex_Ref_t
struct le_mutex * le_mutex_Ref_t
Definition: le_mutex.h:96
le_mutex_CreateRecursive
le_mutex_Ref_t le_mutex_CreateRecursive(const char *nameStr)
le_mutex_Lock
void le_mutex_Lock(le_mutex_Ref_t mutexRef)
le_mutex_TryLock
le_result_t le_mutex_TryLock(le_mutex_Ref_t mutexRef)
le_mutex_CreateNonRecursive
le_mutex_Ref_t le_mutex_CreateNonRecursive(const char *nameStr)
le_mutex_Delete
void le_mutex_Delete(le_mutex_Ref_t mutexRef)
le_mutex_Unlock
void le_mutex_Unlock(le_mutex_Ref_t mutexRef)
LE_DECLARE_INLINE
#define LE_DECLARE_INLINE
Definition: le_basics.h:320