System Signal Handling

Provides functionality to translate Linux System Signals to Ambiorix signal/slot mechanism. More...

Macros
#define	AMXP_SYSSIG_MAX   32
	Defines highest possible system signal. More...

Functions
int	amxp_syssig_enable (const int sigid, const bool enable)
	Enables or disables monitoring of a system signal. More...
bool	amxp_syssig_is_enabled (const int sigid)
	Checks if a system signal is being monitored. More...
int	amxp_syssig_get_fd (void)
	Returns a file descriptor that can be used in an eventloop. More...
int	amxp_syssig_read (void)
	Reads from the file descriptor. More...

Detailed Description

Provides functionality to translate Linux System Signals to Ambiorix signal/slot mechanism.

Handling system signals using the system provided methods have some limitations. In a system signal handler the set of possible system calls that can be done is very limited.

The Ambiorix System Signal API translates a system signal to an Ambiorix signal. To such a signal you can connect many slots (callback functions).

For more information about Ambiorix Signal/Slots

See also

Signal/Slots.

Macro Definition Documentation

AMXP_SYSSIG_MAX

#define AMXP_SYSSIG_MAX   32

Defines highest possible system signal.

Definition at line 95 of file amxp_syssig.h.

Function Documentation

amxp_syssig_enable()

int amxp_syssig_enable	(	const int	sigid,
		const bool	enable
	)

Enables or disables monitoring of a system signal.

When a system signal gets enabled, the signal name is added to the global Ambiorix signal manager. The name of the signal is retrieved using strsignal function.

Note

When enabling a system signal it is possible that other parts of the application that rely on the signal stop working, as the signal is handeld by Ambiorix. So use with caution.

After enabling a signal it is possible to connect slots (callback) functions to it using amxp_slot_connect.

The name of the signal can be retrieved using "strsignal(sigid)".

Parameters

sigid	id of the system signal example SIGUSR1
enable	true to enable monitoring, false to stop monitoring

Returns

0 when signal is successfully enabled and is being monitored

Definition at line 70 of file amxp_syssig.c.

                                                           {
    int retval = -1;
    amxp_signal_t* signal = NULL;
    sigset_t change_mask;
    when_true(sigid > AMXP_SYSSIG_MAX, exit);
    when_true(sigid == SIGKILL || sigid == SIGSTOP, exit);
 
    sigemptyset(&change_mask);
    sigaddset(&change_mask, sigid);
 
    amxp_signal_new(NULL, &signal, strsignal(sigid));
 
    if(enable) {
        when_failed(sigprocmask(SIG_BLOCK, &change_mask, NULL), exit);
        sigaddset(&mask, sigid);
    } else {
        when_failed(sigprocmask(SIG_UNBLOCK, &change_mask, NULL), exit);
        sigdelset(&mask, sigid);
    }
 
    sig_fd = signalfd(sig_fd, &mask, SFD_NONBLOCK | SFD_CLOEXEC);
    retval = 0;
 
exit:
    return retval;
}

amxp_syssig_get_fd()

int amxp_syssig_get_fd

(

void

)

Returns a file descriptor that can be used in an eventloop.

System signal monitoring is done using "signalfd". The filedescriptor must be added to your eventloop to make it work. When data is available on this filedescriptor the function amxp_syssig_read must be called to make sure the correct dispatching is done (calling of the slots)

Returns

A file descriptor or -1 if non is available

Definition at line 110 of file amxp_syssig.c.

                             {
    return sig_fd;
}

amxp_syssig_is_enabled()

bool amxp_syssig_is_enabled

(

const int

sigid

)

Checks if a system signal is being monitored.

If a system signal is enabled for monitoring this function will return true.

Parameters

sigid

id of the system signal example SIGUSR1

Returns

true when the signal was enabled for being monitored

Definition at line 97 of file amxp_syssig.c.

                                             {
    bool enabled = false;
    int inset = -1;
    when_true(sigid > AMXP_SYSSIG_MAX, exit);
 
    inset = sigismember(&mask, sigid);
    when_true(inset < 0, exit);
 
    enabled = (inset == 1);
exit:
    return enabled;
}

amxp_syssig_read()

int amxp_syssig_read

(

void

)

Reads from the file descriptor.

Use this function in an eventloop. When a system signal is received data will become available for read on the signal fd. Use amxp_syssig_get_fd to get the file descriptor and add it to your eventloop.

This function will make sure that all data is read from the file descriptor and that the correct slots are called.

Returns

0 when reading and dispatching is done successful, any other value indicates an error condition.

Definition at line 114 of file amxp_syssig.c.

                           {
    int retval = -1;
    struct signalfd_siginfo si;
    ssize_t res = 0;
    amxc_var_t sig_var;
    int len = sizeof(amxp_siginfo_t);
    amxp_signal_t* signal = NULL;
 
    amxc_var_init(&sig_var);
 
    res = read(sig_fd, &si, len);
    when_true(res != len, exit);
 
    amxc_var_set(amxp_siginfo_t, &sig_var, &si);
 
    signal = amxp_sigmngr_find_signal(NULL, strsignal(si.ssi_signo));
    when_null(signal, exit);
    amxp_signal_trigger(signal, &sig_var);
 
    retval = 0;
 
exit:
    amxc_var_clean(&sig_var);
    return retval;
}