// Set up a signal_info to begin waiting for signal
static int
setup_pipes (signal_info** signals, int count, struct pollfd *fd_structs, int *currfd)
{
int i;
int r = 0;
for (i = 0; i < count; ++i) {
signal_info* h;
int filedes[2];
h = signals [i];
if (mph_int_get (&h->pipecnt) == 0) { // First listener for this signal_info
if ((r = pipe (filedes)) != 0) {
break;
}
mph_int_set (&h->read_fd, filedes [0]);
mph_int_set (&h->write_fd, filedes [1]);
}
mph_int_inc (&h->pipecnt);
fd_structs[*currfd].fd = mph_int_get (&h->read_fd);
fd_structs[*currfd].events = POLLIN;
++(*currfd); // count is verified less than NUM_SIGNALS by caller
}
return r;
}
// This handler is registered once for each UnixSignal object. A pipe is maintained
// for each one; Wait users read at one end of this pipe, and default_handler sends
// a write on the pipe for each signal received while the Wait is ongoing.
//
// Notice a fairly unlikely race condition exists here: Because we synchronize with
// pipe teardown, but not install/uninstall (in other words, we are only trying to
// protect against writing on a closed pipe) it is technically possible a full
// uninstall and then an install could complete after signum is checked but before
// the remaining instructions execute. In this unlikely case count could be
// incremented or a byte written on the wrong signal handler.
static void
default_handler (int signum)
{
int i;
for (i = 0; i < NUM_SIGNALS; ++i) {
int fd;
signal_info* h = &signals [i];
if (mph_int_get (&h->signum) != signum)
continue;
mph_int_inc (&h->count);
if (!acquire_pipelock_handler (&h->pipelock))
continue; // Teardown is occurring on this object, no one to send to.
fd = mph_int_get (&h->write_fd);
if (fd > 0) { // If any listener exists to write to
int j,pipecounter;
char c = signum; // (Value is meaningless)
pipecounter = mph_int_get (&h->pipecnt); // Write one byte per pipe listener
for (j = 0; j < pipecounter; ++j) {
int r;
do { r = write (fd, &c, 1); } while (keep_trying (r));
}
}
release_pipelock_handler (&h->pipelock);
}
}
static int
setup_pipes (signal_info** signals, int count, struct pollfd *fd_structs, int *currfd)
{
int i;
int r = 0;
for (i = 0; i < count; ++i) {
signal_info* h;
int filedes[2];
h = signals [i];
if (mph_int_get (&h->pipecnt) == 0) {
if ((r = pipe (filedes)) != 0) {
break;
}
h->read_fd = filedes [0];
h->write_fd = filedes [1];
}
mph_int_inc (&h->pipecnt);
fd_structs[*currfd].fd = h->read_fd;
fd_structs[*currfd].events = POLLIN;
++(*currfd);
}
return r;
}
// A UnixSignal object is being Disposed
int
Mono_Unix_UnixSignal_uninstall (void* info)
{
#if defined(HAVE_SIGNAL)
signal_info* h;
int r = -1;
if (acquire_mutex (&signals_mutex) == -1)
return -1;
h = info;
if (h == NULL || h < signals || h > &signals [NUM_SIGNALS])
errno = EINVAL;
else {
/* last UnixSignal -- we can unregister */
int signum = mph_int_get (&h->signum);
if (h->have_handler && count_handlers (signum) == 1) {
mph_sighandler_t p = signal (signum, h->handler);
if (p != SIG_ERR)
r = 0;
h->handler = NULL;
h->have_handler = 0;
}
mph_int_set (&h->signum, 0);
}
release_mutex (&signals_mutex);
return r;
#else
g_error ("signal() is not supported by this platform");
return 0;
#endif
}
static inline void
release_pipelock_handler (int *lock)
{
while (1) {
int lockvalue = mph_int_get (lock);
int lockvalue_new = PIPELOCK_INCR_COUNT (lockvalue, -1);
if (mph_int_test_and_set (lock, lockvalue, lockvalue_new))
return;
}
}
static int
count_handlers (int signum)
{
int i;
int count = 0;
for (i = 0; i < NUM_SIGNALS; ++i) {
if (mph_int_get (&signals [i].signum) == signum)
++count;
}
return count;
}
static inline void
release_pipelock_teardown (int *lock)
{
while (1) {
int lockvalue = mph_int_get (lock);
int lockvalue_new = lockvalue & ~PIPELOCK_TEARDOWN_BIT;
// Technically this can't fail, because we hold both the pipelock and the mutex, but
if (mph_int_test_and_set (lock, lockvalue, lockvalue_new))
return;
}
}
static inline void
acquire_pipelock_teardown (int *lock)
{
int lockvalue_draining;
// First mark that a teardown is occurring, so handlers will stop entering the lock.
while (1) {
int lockvalue = mph_int_get (lock);
lockvalue_draining = lockvalue | PIPELOCK_TEARDOWN_BIT;
if (mph_int_test_and_set (lock, lockvalue, lockvalue_draining))
break;
}
// Now wait for all handlers to complete.
while (1) {
if (0 == PIPELOCK_GET_COUNT (lockvalue_draining))
break; // We now hold the lock.
// Handler is still running, spin until it completes.
sched_yield (); // We can call this because !defined(HOST_WIN32)
lockvalue_draining = mph_int_get (lock);
}
}
// Cleanup a signal_info after waiting for signal
static void
teardown_pipes (signal_info** signals, int count)
{
int i;
for (i = 0; i < count; ++i) {
signal_info* h = signals [i];
if (mph_int_dec_test (&h->pipecnt)) { // Final listener for this signal_info
acquire_pipelock_teardown (&h->pipelock);
int read_fd = mph_int_get (&h->read_fd);
int write_fd = mph_int_get (&h->write_fd);
if (read_fd != 0)
close (read_fd);
if (write_fd != 0)
close (write_fd);
mph_int_set (&h->read_fd, 0);
mph_int_set (&h->write_fd, 0);
release_pipelock_teardown (&h->pipelock);
}
}
}
// Return 1 for success
static inline int
acquire_pipelock_handler (int *lock)
{
while (1) {
int lockvalue = mph_int_get (lock);
if (lockvalue & PIPELOCK_TEARDOWN_BIT) // Final lock is being torn down
return 0;
int lockvalue_new = PIPELOCK_INCR_COUNT (lockvalue, 1);
if (mph_int_test_and_set (lock, lockvalue, lockvalue_new))
return 1;
}
}
static void
default_handler (int signum)
{
int i;
for (i = 0; i < NUM_SIGNALS; ++i) {
int fd;
signal_info* h = &signals [i];
if (mph_int_get (&h->signum) != signum)
continue;
mph_int_inc (&h->count);
fd = mph_int_get (&h->write_fd);
if (fd > 0) {
int j,pipecounter;
char c = signum;
pipecounter = mph_int_get (&h->pipecnt);
for (j = 0; j < pipecounter; ++j) {
int r;
do { r = write (fd, &c, 1); } while (keep_trying (r));
}
}
}
}
// Given pipes set up, wait for a byte to arrive on one of them
static int
wait_for_any (signal_info** signals, int count, int *currfd, struct pollfd* fd_structs, int timeout, Mono_Posix_RuntimeIsShuttingDown shutting_down)
{
int r, idx;
// Poll until one of this signal_info's pipes is ready to read.
// Once a second, stop to check if the VM is shutting down.
do {
struct timeval tv;
struct timeval *ptv = NULL;
if (timeout != -1) {
tv.tv_sec = timeout / 1000;
tv.tv_usec = (timeout % 1000)*1000;
ptv = &tv;
}
r = poll (fd_structs, count, timeout);
} while (keep_trying (r) && !shutting_down ());
idx = -1;
if (r == 0)
idx = timeout;
else if (r > 0) { // The pipe[s] are ready to read.
int i;
for (i = 0; i < count; ++i) {
signal_info* h = signals [i];
if (fd_structs[i].revents & POLLIN) {
int r;
char c;
do {
r = read (mph_int_get (&h->read_fd), &c, 1);
} while (keep_trying (r) && !shutting_down ());
if (idx == -1)
idx = i;
}
}
}
return idx;
}
// A UnixSignal object is being constructed
void*
Mono_Unix_UnixSignal_install (int sig)
{
#if defined(HAVE_SIGNAL)
int i;
signal_info* h = NULL; // signals[] slot to install to
int have_handler = 0; // Candidates for signal_info handler fields
void* handler = NULL;
if (acquire_mutex (&signals_mutex) == -1)
return NULL;
#if defined (SIGRTMIN) && defined (SIGRTMAX)
/*The runtime uses some rt signals for itself so it's important to not override them.*/
if (sig >= SIGRTMIN && sig <= SIGRTMAX && count_handlers (sig) == 0) {
struct sigaction sinfo;
sigaction (sig, NULL, &sinfo);
if (sinfo.sa_handler != SIG_DFL || (void*)sinfo.sa_sigaction != (void*)SIG_DFL) {
pthread_mutex_unlock (&signals_mutex);
errno = EADDRINUSE;
return NULL; // This is an rt signal with an existing handler. Bail out.
}
}
#endif /*defined (SIGRTMIN) && defined (SIGRTMAX)*/
// Scan through signals list looking for (1) an unused spot (2) a usable value for handler
for (i = 0; i < NUM_SIGNALS; ++i) {
int just_installed = 0;
// We're still looking for a signal_info spot, and this one is available:
if (h == NULL && mph_int_get (&signals [i].signum) == 0) {
h = &signals [i];
h->handler = signal (sig, default_handler);
if (h->handler == SIG_ERR) {
h->handler = NULL;
h = NULL;
break;
}
else {
just_installed = 1;
}
}
// Check if this slot has a "usable" (not installed by this file) handler-to-restore-later:
// (On the first signal to be installed, signals [i] will be == h when this happens.)
if (!have_handler && (just_installed || mph_int_get (&signals [i].signum) == sig) &&
signals [i].handler != default_handler) {
have_handler = 1;
handler = signals [i].handler;
}
if (h && have_handler) // We have everything we need
break;
}
if (h) {
// If we reached here without have_handler, this means that default_handler
// was set as the signal handler before the first UnixSignal object was installed.
g_assert (have_handler);
// Overwrite the tenative handler we set a moment ago with a known-usable one
h->handler = handler;
h->have_handler = 1;
mph_int_set (&h->count, 0);
mph_int_set (&h->pipecnt, 0);
mph_int_set (&h->signum, sig);
}
release_mutex (&signals_mutex);
return h;
#else
g_error ("signal() is not supported by this platform");
return 0;
#endif
}
