sa_handler function; can't access class member - c++

Question

I am trying to build a multi threaded program that will create four instances of a Child and "run" a set of "expensive" Jobs. The parent will send a signal indicating when they shall all start. Now, each child thread must then catch that signal. It has inside of it a sig_handler. It's a private class inside of Child.
So far I have it defined as:
private:
class sig_handler {
typedef struct sigaction sigAct;
Shared* sh;
//============
void whatSig();
public:
sig_handler( Shared* s );
sigAct action;
sigset_t signalset; // Just want siguser and sigquit
static void catchSig( int sig ); // interacts with the shared resource
// it starts up the threads
};
First off, is it even ok to have a class as a signal handler? If it is ok (which would certainly make the readibility better), how would we implement it?
I am trying to catch SIGUSR1 so that I can change a flag in Shared memory. Each thread has access to Shared memory through a pointer to this object, i.e. Shared* share. This is done using a class to act as a kind of shared base.
Now here is what I really need answered. I begin setting up my sigset_t signalSet:
Child::sig_handler::sig_handler( Shared* s ) {
sh = s;
sigemptyset(&signalset);
sigaddset(&signalset, SIGUSR1); // Add these to the now empty set
sigaddset(&signalset, SIGQUIT);
action.sa_handler = catchSig; // 1
action.sa_mask = signalset;
action.sa_flags = 0;
sigaction(SIGUSR1, &action, NULL); // attach the class member action
}
Really pay attention to line 1. This is a critical spot. This I think has to be a static or global function. This is where an error can be happening. When I make my class method catchSig(int sig) non static, line 1 complains Reference to a non-static function call must be called. I have it defined as such when this happens: void catchSig( int sig );
When I define it as static void catchSig( int sig );, the compiler complains on line 2.
void Child::sig_handler::catchSig(int sig) {
sh->startflag; // 2
}
It says, Invalid use of 'sh' in static member function. I need to be able to have access to this variable. How can I fix it so that I can have my sig_handler class, and share through catchSig()?
Update:
I implemented StoryTeller's suggestion of using a pointer to this. While it worked to stop the complaining of the compiler, I still have a buildtime error. I altered the definition of sig_handler to now be this:
private:
class sig_handler {
typedef struct sigaction sigAct;
Shared* sh;
static sig_handler* self;
//============
void whatSig();
public:
sig_handler( Shared* s );
sigAct action;
sigset_t signalset;
static void catchSig( int sig ); // interacts with the shared resource
// it starts up the threads
};
Take note of the new static pointer to itself. This was done so that I can have access to the variable sh, the shared resource that I need. Which I use as such:
void Child::sig_handler::catchSig(int sig) {
self->sh->setStartFlag(true); // this was were it used to complain
}
The sig_handler is created in the Child constructor (sigHand = new sig_handler(share)). I get a build time error stated below. What is happening? How can this be fixed?
"Child::sig_handler::self", referenced from:
Child::sig_handler::sig_handler(Shared*) in Child.o
Child::sig_handler::catchSig(int) in Child.o
ld: symbol(s) not found for architecture x86_64
Update 2:
Essentially, it's not possible to make a sig_handler class unfortunately.