Re: Assigning a member function to signal callback function pointer

"" <>
Wed, 24 Dec 2008 18:31:40 -0800 (PST)
On Dec 24, 7:04 pm, Ramesh <> wrote:


I am writing an application in linux using timer_create API to create
timers in my application, I have registered a call back routine which
would be called when the timer timesout. I get the following error:


test.cpp: In member function 'unsigned long
testMgr::addConfigChangeTimer(unsigned long)':
test.cpp:125: error: argument of type 'void (testMgr::)(sigval_t)'
does not match 'void (*)(sigval_t)'


The compiler expects a function returning void and taking a sigval_t
as argument, in my case the only difference is that the linkage is C++
style and its a member function.

Is there a way I can assign a member function to the notify_function


Here is the code snippet:


// Actual point of assignment of the callback function to the signal

unsigned long testMgr::addConfigChangeTimer(unsigned long interval) {

    timer_t id = 0;
    int count = 0;
    struct sigevent sig;
    struct itimerspec timerspec;

    memset(&timerspec, 0, sizeof(struct itimerspec));
    memset(&sig, 0, sizeof(struct sigevent));

    sig.sigev_notify = SIGEV_THREAD;
    sig.sigev_notify_function = ConfigChangeHandler;

    sig.sigev_value.sival_ptr = (void*)&count

Do you actually mean to pass the address of the local variable count
to an asynchronous callback function here?

Anyways, like Sam said you can't pass a pointer to a member function
as a callback and expect it to be called on the appropriate instance
of the object. Pointer-to-members do exist, and you can use them but
only if you also supply an instance of a class. The compiler error you
received is because you attempted to pass a pointer to a non-static
member function but it was expecting a pointer to a static/non-member
function (the two have different types).

Instead, pass your 'this' pointer through sig.sigev_value.sival_ptr,
and make your callback a static function. Then your callback can
either do what it needs to do or pass control off to a non-static
member function appropriately, e.g.:

class testMgr {
  unsigned long addConfigChangeTimer (unsigned long);
  void ConfigChangeHandler ();
  static void StaticConfigChangeHandler (sigval_t value);

unsigned long testMgr::addConfigChangeTimer (unsigned long) {
  sig.sigev_notify_function = StaticConfigChangeHandler;
  sig.sigev_value.sival_ptr = (void *)this;

void testMgr::StaticConfigChangeHandler (sigval_t value) {
  // pass control to member function.
  ((testMgr *)value.sival_ptr)->ConfigChangeHandler();

void testMgr::ConfigChangeHandler () {
  // do stuff.

If you want to pass additional context data to ConfigChangeHandler
then you'll have to pack stuff in to some kind of structure, e.g.:

struct ConfigChangeHandlerParams {
  ConfigChangeHandler *inst;
  int *pcount;

void testMgr::StaticConfigChangeHandler (sigval_t value) {
  // for example, passing pcount:
  ConfigChangeHandlerParams *p = (ConfigChangeHandlerParams *)

Managing ConfigChangeHandlerParams structs in an exception-safe way is
left as an exercise.



// Actual function

void testMgr::ConfigChangeHandler(sigval_t value) {

    ACE_Guard<ACE_Thread_Mutex> guard(tMutex);

    if (ConfigChange == TRUE) {
        ConfigChange = FALSE;
    trace("Config change timeout process completed");



// Class definition

class testMgr {


                timestamp ChangeTime;
                BOOL Confi=


                ACE_Thread_Mutex tMutex;


                UINT32 addConfigChange=


                void entConfigChan=

geHandler(sigval_t );


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