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<title>FBB::Signal</title>
<link rev="made" href="mailto:Frank B. Brokken: f.b.brokken@rug.nl">
</head>
<body text="#27408B" bgcolor="#FFFAF0">
<hr>
<h1>FBB::Signal</h1>
<h2>libbobcat-dev_3.19.01-x.tar.gz</h2>
<h2>2005-2013</h2>
<html><head>
<link rev="made" href="mailto:Frank B. Brokken: f.b.brokken@rug.nl">
</head>
<body text="#27408B" bgcolor="#FFFAF0">
<hr>
<h1></h1>
<html><head>
<title>FBB::Signal(3bobcat)</title>
<link rev="made" href="mailto:Frank B. Brokken: f.b.brokken@rug.nl">
</head>
<body text="#27408B" bgcolor="#FFFAF0">
<hr>
<h1>FBB::Signal(3bobcat)</h1>
<h2>libbobcat-dev_3.19.01-x.tar.gz signal handler</h2>
<h2>2005-2013</h2>
<p>
<h2>NAME</h2>FBB::Signal - Signal Handler
<p>
<h2>SYNOPSIS</h2>
<strong>#include <bobcat/signal></strong><br>
Linking option: <em>-lbobcat</em>
<p>
<h2>DESCRIPTION</h2>
<p>
Signals have the well known drawback that signals arrive free of
context. E.g., assume a program runs a flow control loop like this:
<pre>
void Class::run()
{
while (d_continue)
handleTasks();
cleanup();
}
</pre>
then if the program needs to recognize a termination signal then the
typical signal handler looks like this:
<pre>
void signalHandler(int signal)
{
// perform required actions
}
</pre>
Since the <em>signalHandler</em> 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:
<pre>
// 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;
}
</pre>
The class <em>Signal</em> 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.
<p>
The signal is now handled by an object, whose class must define a member
<pre>
void signalHandler(size_t signum) override;
</pre>
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).
<p>
Note that, as the signal may arrive at unpredicable times data members
that can be modified by <em>signalHandler</em> should be declared using the
<em>volatile</em> modifier. Moreover, data that can be modified by
the <em>signalHandler</em> member and by other class members should be protected
by <em>mutexes</em> (cf. the <strong>C++-11</strong> class <em>std::mutex</em> or
<strong>pthread_mutex_lock</strong>(3posix)).
<p>
<h2>NAMESPACE</h2>
<strong>FBB</strong><br>
All constructors, members, operators and manipulators, mentioned in this
man-page, are defined in the namespace <strong>FBB</strong>.
<p>
<h2>INHERITS FROM</h2>
<em>Signal</em> is not derived from other classes, but the classes for which
signals must be handled by <em>Signal</em> must themselves publicly be derived from
the class <em>FBB::SignalHandler</em> and must implement a member
<pre>
virtual void signalHandler(size_t signum) override;
</pre>
handling the received signal.
<p>
<h2>CONSTRUCTORS AND OVERLOADED OPERATORS</h2>
<em>Signal</em> is defined as a <em>singleton</em>, and does not offer public or
protected constructors, nor does it offer overloaded operators.
<p>
<h2>STATIC MEMBER FUNCTION</h2>
<ul>
<li> <strong>static Signal &instance()</strong>:<br><br>
This static member can be used to access a reference to the program's
single <em>Signal</em> object.
</ul>
<p>
<h2>MEMBER FUNCTIONS</h2>
All of <em>Signal</em>'s member functions can only be called through a
reference to the program's <em>Signal</em> object, returning a reference to the
program's single <em>Signal</em> object:
<ul>
<li> <strong>void add(size_t signum, SignalHandler &object)</strong>:<br><br>
<em>SignalHandler object</em> is activated on arrival of signal
<em>signum</em>. If multiple <em>SignalHandler</em> objects must be called then
multiple <em>Signal::add</em> calls can be provided, and the various
<em>SignalHandler::signalHandler</em> members are called in the same
sequence as their respective <em>Signal::add</em> calls. If one of the
earlier <em>signalHandler</em> members terminates the program then later
<em>signalHandler</em> members are not activated anymore. If
<em>Signal::add</em> is called by, e.g., an object's constructor, then its
destructor should call <em>Signal::remove</em> to prevent the object's
signal handler from being called after its destruction.
<li> <strong>void remove(size_t signum, SignalHandler &object)</strong>:<br><br>
<em>SignalHandler object</em> for signal <em>signum</em> is removed from the
<em>Signal</em> object. It is the responsibility of <em>object</em> to
deregister itself from <em>Signal</em> just before <em>object</em> goes out of
scope. Objects can only deregister themselves if they've previously
registered themselves using <em>add</em>.
<li> <strong>void ignore(size_t signum)</strong>:<br><br>
Any previously installed <em>SignalHandler</em> object is no longer
activated on arrival of signal <em>signum</em>. In addition, if possible,
signal <em>signum</em> is completely ignored (some signals cannot be
caught, blocked, of ignored, like <em>SIGKILL</em> and <em>SIGSTOP</em>
(cf. <strong>signal</strong>(7))).
<li> <strong>void reset(size_t signum)</strong>:<br><br>
Any previously installed <em>SignalHandler</em> object is no longer
activated on arrival of signal <em>signum</em>. In addition, the default
action the program takes on arrival of signal <em>signum</em> is
reinstalled (cf. <strong>signal</strong>(7)).
</ul>
<p>
If the <em>signum</em> value that is passed to <em>Signal</em>'s members is not a
defined signal value, then an <strong>FBB::Exception</strong> exception is thrown.
<p>
<h2>EXAMPLE</h2>
<pre>
#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:
virtual 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 SIGHUP or SIGTERM... to process " << d_pid << endl;
sleep(1);
}
cout << "Ending `run' after receiving signal " << d_signal << endl;
}
void SignalDemo::signalHandler(size_t signal)
{
if (signal == SIGHUP)
cout << "Process " << d_pid << " received SIGHUP" << 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(SIGHUP, signalDemo);
Signal::instance().add(SIGTERM, signalDemo);
signalDemo.run();
}
</pre>
<p>
<h2>FILES</h2>
<em>bobcat/signal</em> - defines the class interface
<p>
<h2>SEE ALSO</h2>
<strong>bobcat</strong>(7), <strong>pthread_mutex_lock</strong>(3posix), <strong>signal</strong>(7),<br>
and the <strong>C++-11</strong> class <em>std::mutex</em>.
<p>
<h2>BUGS</h2>
None Reported.
<p>
<h2>DISTRIBUTION FILES</h2>
<ul>
<li> <em>bobcat_3.19.01-x.dsc</em>: detached signature;
<li> <em>bobcat_3.19.01-x.tar.gz</em>: source archive;
<li> <em>bobcat_3.19.01-x_i386.changes</em>: change log;
<li> <em>libbobcat1_3.19.01-x_*.deb</em>: debian package holding the
libraries;
<li> <em>libbobcat1-dev_3.19.01-x_*.deb</em>: debian package holding the
libraries, headers and manual pages;
<li> <em>http://sourceforge.net/projects/bobcat</em>: public archive location;
</ul>
<p>
<h2>BOBCAT</h2>
Bobcat is an acronym of `Brokken's Own Base Classes And Templates'.
<p>
<h2>COPYRIGHT</h2>
This is free software, distributed under the terms of the
GNU General Public License (GPL).
<p>
<h2>AUTHOR</h2>
Frank B. Brokken (<strong>f.b.brokken@rug.nl</strong>).
<p>
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