| FBB::Signal(3bobcat) | signal handler | FBB::Signal(3bobcat) |
FBB::Signal - Signal Handler
#include <bobcat/signal>
Linking option: -lbobcat
Signals have the well known drawback that signals arrive free of context. E.g., assume a program runs a flow control loop like this:
void Class::run()
{
while (d_continue)
handleTasks();
cleanup();
}
then if the program needs to recognize a termination signal then the typical signal handler looks like this:
void signalHandler(int signal)
{
// perform required actions
}
Since the signalHandler is called asynchronically, there is no context available, and the usual way of communicating between objects and signal handlers is via static variables, like this:
// declared as static bool s_continue;
bool Class::s_continue = true;
void Class::run()
{
while (s_continue)
handleTasks();
cleanup();
}
// declared as static void signalHander(int signal);
void Class::signalHandler(int signal)
{
s_continue = false;
}
The class Signal allows the signal handler to operate in the context of a class. The advantage of this is that static data members are no longer required and that the signal may be used to control data members of individual objects.
The signal is now handled by an object, whose class must define a member
and this function is responsible for handling the received signal. Since it is a member function it may affect its object’s local variables and it may call its object’s member functions. Static data members are not required anymore (see below for an example).
void signalHandler(size_t signum) override;
Note that, as the signal may arrive at unpredicable times data members that can be modified by signalHandler should be declared using the volatile modifier. Moreover, data that can be modified by the signalHandler member and by other class members should be protected by mutexes (cf. the C++-11 class std::mutex or pthread_mutex_lock(3posix)).
FBB
All constructors, members, operators and manipulators, mentioned in this
man-page, are defined in the namespace FBB.
Signal is not derived from other classes, but the classes for which signals must be handled by Signal must themselves publicly be derived from the class FBB::SignalHandler and must implement a member
void signalHandler(size_t signum) override;
handling the received signal.
Signal is defined as a singleton, and does not offer public or protected constructors, nor does it offer overloaded operators.
All of Signal’s member functions can only be called through a reference to the program’s Signal object, returning a reference to the program’s single Signal object:
If the signum value that is passed to Signal’s members is not a defined signal value, then an FBB::Exception exception is thrown.
#include <sys/types.h>
#include <unistd.h>
#include <iostream>
#include "../signal"
class SignalDemo: public FBB::SignalHandler
{
volatile size_t d_signal;
volatile bool d_continue;
pid_t d_pid;
public:
SignalDemo();
void run();
private:
void signalHandler(size_t signum) override;
};
using namespace std;
using namespace FBB;
SignalDemo::SignalDemo()
:
d_signal(0),
d_continue(true),
d_pid(getpid())
{}
void SignalDemo::run()
{
while (d_continue)
{
cout << "Send a SIGINT (2) or SIGTERM (15) ... to process " <<
d_pid << endl;
sleep(1);
}
cout << "Ending `run’ after receiving signal " << d_signal << endl;
}
void SignalDemo::signalHandler(size_t signal)
{
if (signal == SIGINT)
cout << "Process " << d_pid << " received SIGINT" << endl;
else if (signal == SIGTERM)
{
cout << "Process " << d_pid << " received SIGTERM" << endl;
d_signal = SIGTERM;
d_continue = false;
}
}
int main()
{
SignalDemo signalDemo;
Signal::instance().add(SIGINT, signalDemo);
Signal::instance().add(SIGTERM, signalDemo);
signalDemo.run();
}
bobcat/signal - defines the class interface
bobcat(7), pthread_mutex_lock(3posix),
signal(7),
and the C++-11 class std::mutex.
None Reported.
Bobcat is an acronym of `Brokken’s Own Base Classes And Templates’.
This is free software, distributed under the terms of the GNU General Public License (GPL).
Frank B. Brokken (f.b.brokken@rug.nl).
| 2005-2020 | libbobcat-dev_5.07.00 |