信号在android源码/external/pppd 源码项目中的应用解读分析

pppoe里面也有信号的处理的方式，

直接上源码：

static void
setup_signals()
{
struct sigaction sa;

/*
* Compute mask of all interesting signals and install signal handlers
* for each. Only one signal handler may be active at a time. Therefore,
* all other signals should be masked when any handler is executing.
*/
sigemptyset(&signals_handled);
sigaddset(&signals_handled, SIGHUP);
sigaddset(&signals_handled, SIGINT);
sigaddset(&signals_handled, SIGTERM);
sigaddset(&signals_handled, SIGCHLD);
sigaddset(&signals_handled, SIGUSR2);

#define SIGNAL(s, handler) do { \
sa.sa_handler = handler; \
if (sigaction(s, &sa, NULL) < 0) \
fatal("Couldn't establish signal handler (%d): %m", s); \
} while (0)

sa.sa_mask = signals_handled;
sa.sa_flags = 0;
SIGNAL(SIGHUP, hup); /* Hangup */
SIGNAL(SIGINT, term); /* Interrupt */
SIGNAL(SIGTERM, term); /* Terminate */
SIGNAL(SIGCHLD, chld);

SIGNAL(SIGUSR1, toggle_debug); /* Toggle debug flag */
SIGNAL(SIGUSR2, open_ccp); /* Reopen CCP */

/*
* Install a handler for other signals which would otherwise
* cause pppd to exit without cleaning up.
*/
SIGNAL(SIGABRT, bad_signal);
SIGNAL(SIGALRM, bad_signal);
SIGNAL(SIGFPE, bad_signal);
SIGNAL(SIGILL, bad_signal);
SIGNAL(SIGPIPE, bad_signal);
SIGNAL(SIGQUIT, bad_signal);
SIGNAL(SIGSEGV, bad_signal);
/*
* Apparently we can get a SIGPIPE when we call syslog, if
* syslogd has died and been restarted. Ignoring it seems
* be sufficient.
*/
signal(SIGPIPE, SIG_IGN);
}

这里面和之前的dhcp以及dnsmasq不一样，单纯信号函数接口和对应的hangler处理
上面对每一种有单独的处理方式，分别来看。

/*
* hup - Catch SIGHUP signal.
*
* Indicates that the physical layer has been disconnected.
* We don't rely on this indication; if the user has sent this
* signal, we just take the link down.
*/
static void
hup(sig)
int sig;
{
/* can't log a message here, it can deadlock */
got_sighup = 1;
if (conn_running)
/* Send the signal to the [dis]connector process(es) also */
kill_my_pg(sig);
notify(sigreceived, sig);
if (waiting)
siglongjmp(sigjmp, 1);
}这里面由一个重要的知识点，siglongjump，需要后面补充下！
着重讨论下面的case：用户主动关闭这个进程的操作，和前面是一样的。

/*
* term - Catch SIGTERM signal and SIGINT signal (^C/del).
*
* Indicates that we should initiate a graceful disconnect and exit.
*/
/*ARGSUSED*/
static void
term(sig)
int sig;
{
/* can't log a message here, it can deadlock */
got_sigterm = sig;
if (conn_running)
/* Send the signal to the [dis]connector process(es) also */
kill_my_pg(sig);
notify(sigreceived, sig);
if (waiting)
siglongjmp(sigjmp, 1);
}下面主要为了保持同步而接收的信号，
/*
* chld - Catch SIGCHLD signal.
* Sets a flag so we will call reap_kids in the mainline.
*/
static void
chld(sig)
int sig;
{
got_sigchld = 1;
if (waiting)
siglongjmp(sigjmp, 1);
}


加一个标志位，表示子进程已经退出，需要主进程做相应的动作。