Provided by: libbobcat-dev_3.19.01-1ubuntu1_amd64 
NAME
FBB::Fork - Implements fork(2) using the Template Design Pattern
SYNOPSIS
#include <bobcat/fork>
Linking option: -lbobcat
DESCRIPTION
FBB::Fork objects may be used to implement the fork(2) call as part of the Template
Algorithm Design Pattern. The class was designed as a virtual base class for classes
implementing the essential parts of the forking process. The class is a virtual base
class. Derived classes must implement the members childProcess() and parentProcess() as
part of the `Template Method Design Pattern’ (see Gamma et al., 1995).
Terminating child processes send SIGCHLD signals to their parents. The C library offers
the following macros to analyze the status values received by the parent process using a
wait(2) or waitpid(2) system call:
o int WIFEXITED(int status):
This macro returns a nonzero value if the child process terminated normally with
`exit’ or `_exit’.
o int WEXITSTATUS(int status):
If `WIFEXITED’ is true of `status’, this macro returns the low-order 8 bits of the
exit status value from the child process.
o int WIFSIGNALED(int status):
This macro returns a nonzero value if the child process terminated because it
received a signal that was not handled.
o int WTERMSIG(int status):
If `WIFSIGNALED’ is true of `status’, this macro returns the signal number of the
signal that terminated the child process.
o int WCOREDUMP(int status):
This macro returns a nonzero value if the child process terminated and produced a
core dump.
o int WIFSTOPPED(int status):
This macro returns a nonzero value if the child process is stopped.
o int WSTOPSIG(int status):
If `WIFSTOPPED’ is true of `status’, this macro returns the signal number of the
signal that caused the child process to stop.
NAMESPACE
FBB
All constructors, members, operators and manipulators, mentioned in this man-page, are
defined in the namespace FBB.
INHERITS FROM
-
CONSTRUCTORS
o Fork():
This is the only available constructor. Note that there is no copy constructor.
DESTRUCTOR
o virtual ~Fork():
Derived classes may define their own destructor, which is called when the ~Fork()
destructor is activated.
MEMBER FUNCTIONS
o void fork():
Performs the actual forking. It is implemented in such a way that the corresponding
parent- and child- processes are activated from virtual members of FBB::Fork. If
the forking operation fails, an FBB::Exception exception is thrown.
PROTECTED MEMBER FUNCTIONS
o virtual void childProcess() = 0:
This member must be implemented by derived classes. It defines the actions that are
performed by the child process, following the fork(2) system call. Just before
childProcess() is called, childRedirections() (see below) has been executed. The
childProcess() function should terminate the child process. A good way to do this
is to throw an exeption which is caught by main()’s function try block. Terminating
a process using exit(2) is deprecated in C++.
o virtual void childRedirections():
This function may be redefined in derived classes to set up the redirections that
are necessary to communicate with the parent process. See also the classes
redirector(3bobcat), pipe(3bobcat), ipipe(3bobcat) and opipe(3bobcat). By default,
childRedirections() does nothing.
o virtual void parentProcess() = 0:
This member must be implemented by derived classes. It defines the actions that are
performed by the parent process, following the fork(2) system call. Just before
parentProcess() is called, parentRedirections() (see below) has been executed.
o virtual void parentRedirections():
This function may be redefined in derived classes to set up the redirections that
are necessary to communicate with, e.g., the parent. See, e.g., the classes
redirector(3bobcat), pipe(3bobcat), ipipe(3bobcat) and opipe(3bobcat). By default,
parentRedirections() does nothing.
o pid_t pid() const:
Returns the child’s process id in the parent’s code (i.e., in the parent-members
below), and 0 in the child’s code (i.e., in the child-members below). Note that the
value of pid() is undefined when called before the member fork() has been called.
o void prepareDaemon() const:
Prepares for a daemon childprocess. This function may (should) be called from
childProcess() to ensure that the child process changes its current working
directory to the root (/) directory, thus freeing up mount points; that the child
process starts a new session/process group to allow the parent (group leader) to
kill all its processes without terminating the daemon; and makes sure that the
child process closes and reopens the standard streams by associating them with
/dev/null to prevent ghost input and output actions from interfering with the
daemon’s actions. An FBB::Exception is thrown if changing directory to the root
directory fails.
o int waitForChild():
This member may be called by parentProcess() to wait for the completion of the
child-process. The return value (exit-code) of the child process is returned as a
value between 0 and 255. If the child process terminates before the completion of
the parent process, then waitForChild() should be called to prevent zombies from
occurring. Alternatively, the parent process may terminate (e.g., using exit(2))
while the child process is still alive. This is the normal way to create a daemon
process.
EXAMPLE
#include <iostream>
#include <unistd.h>
#include <bobcat/fork>
using namespace std;
using namespace FBB;
class Background: public Fork
{
public:
void childProcess();
void parentProcess();
};
void Background::childProcess()
{
for (int idx = 0; idx < 3; ++idx)
{
cout << "Hello world # " << idx << endl;
sleep(1);
}
throw 0; // caught in main()
}
void Background::parentProcess()
{
cout << "Waiting for the child process to end...\n";
cout << "The child returns value " << waitForChild() << endl;
}
int main()
try
{
Background bg;
bg.fork();
cout << "This is from the parent\n";
return 0;
}
catch(int x)
{
cout << "The child terminates with: " << x << endl;
return x;
}
FILES
bobcat/fork - defines the class interface
SEE ALSO
bobcat(7), ipipe(3bobcat), fork(2), opipe(3bobcat), pipe(3bobcat), redirector(3bobcat),
wait(2), waitpid(2)
BUGS
None Reported.
DISTRIBUTION FILES
o bobcat_3.19.01-x.dsc: detached signature;
o bobcat_3.19.01-x.tar.gz: source archive;
o bobcat_3.19.01-x_i386.changes: change log;
o libbobcat1_3.19.01-x_*.deb: debian package holding the libraries;
o libbobcat1-dev_3.19.01-x_*.deb: debian package holding the libraries, headers and
manual pages;
o http://sourceforge.net/projects/bobcat: public archive location;
BOBCAT
Bobcat is an acronym of `Brokken’s Own Base Classes And Templates’.
COPYRIGHT
This is free software, distributed under the terms of the GNU General Public License
(GPL).
AUTHOR
Frank B. Brokken (f.b.brokken@rug.nl).