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/* -----------------------------------------------------------------------------
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* (c) The GHC Team, 1998-2005
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* Signal processing / handling.
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* ---------------------------------------------------------------------------*/
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#include "PosixSource.h"
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#include "RtsSignals.h"
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#ifdef alpha_HOST_ARCH
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# if defined(linux_HOST_OS)
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# include <machine/fpu.h>
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# include <sys/eventfd.h>
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/* This curious flag is provided for the benefit of the Haskell binding
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* to POSIX.1 to control whether or not to include SA_NOCLDSTOP when
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* installing a SIGCHLD handler.
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/* -----------------------------------------------------------------------------
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* The table of signal handlers
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* -------------------------------------------------------------------------- */
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#if defined(RTS_USER_SIGNALS)
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/* SUP: The type of handlers is a little bit, well, doubtful... */
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StgInt *signal_handlers = NULL; /* Dynamically grown array of signal handlers */
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static StgInt nHandlers = 0; /* Size of handlers array */
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static nat n_haskell_handlers = 0;
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/* -----------------------------------------------------------------------------
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* Allocate/resize the table of signal handlers.
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* -------------------------------------------------------------------------- */
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more_handlers(int sig)
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if (signal_handlers == NULL)
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signal_handlers = (StgInt *)stgMallocBytes((sig + 1) * sizeof(StgInt), "more_handlers");
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signal_handlers = (StgInt *)stgReallocBytes(signal_handlers, (sig + 1) * sizeof(StgInt), "more_handlers");
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for(i = nHandlers; i <= sig; i++)
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// Fill in the new slots with default actions
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signal_handlers[i] = STG_SIG_DFL;
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// Here's the pipe into which we will send our signals
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static int io_manager_wakeup_fd = -1;
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static int io_manager_control_fd = -1;
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#define IO_MANAGER_WAKEUP 0xff
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#define IO_MANAGER_DIE 0xfe
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#define IO_MANAGER_SYNC 0xfd
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setIOManagerWakeupFd (int fd)
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// only called when THREADED_RTS, but unconditionally
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// compiled here because System.Event.Control depends on it.
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io_manager_wakeup_fd = fd;
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setIOManagerControlFd (int fd)
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// only called when THREADED_RTS, but unconditionally
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// compiled here because System.Event.Control depends on it.
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io_manager_control_fd = fd;
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ioManagerWakeup (void)
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// Wake up the IO Manager thread by sending a byte down its pipe
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if (io_manager_wakeup_fd >= 0) {
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#if defined(HAVE_EVENTFD)
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StgWord64 n = (StgWord64)IO_MANAGER_WAKEUP;
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r = write(io_manager_wakeup_fd, (char *) &n, 8);
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StgWord8 byte = (StgWord8)IO_MANAGER_WAKEUP;
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r = write(io_manager_wakeup_fd, &byte, 1);
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if (r == -1) { sysErrorBelch("ioManagerWakeup: write"); }
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#if defined(THREADED_RTS)
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// Ask the IO Manager thread to exit
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if (io_manager_control_fd >= 0) {
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StgWord8 byte = (StgWord8)IO_MANAGER_DIE;
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r = write(io_manager_control_fd, &byte, 1);
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if (r == -1) { sysErrorBelch("ioManagerDie: write"); }
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io_manager_control_fd = -1;
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io_manager_wakeup_fd = -1;
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ioManagerStartCap (Capability *cap)
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cap,&base_GHCziConcziIO_ensureIOManagerIsRunning_closure,NULL);
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ioManagerStart (void)
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// Make sure the IO manager thread is running
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if (io_manager_control_fd < 0 || io_manager_wakeup_fd < 0) {
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cap = ioManagerStartCap(cap);
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#if !defined(THREADED_RTS)
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#define N_PENDING_HANDLERS 16
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siginfo_t pending_handler_buf[N_PENDING_HANDLERS];
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siginfo_t *next_pending_handler = pending_handler_buf;
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#endif /* THREADED_RTS */
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/* -----------------------------------------------------------------------------
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* Low-level signal handler
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* Places the requested handler on a stack of pending handlers to be
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* started up at the next context switch.
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* -------------------------------------------------------------------------- */
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generic_handler(int sig USED_IF_THREADS,
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#if defined(THREADED_RTS)
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if (io_manager_control_fd != -1)
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StgWord8 buf[sizeof(siginfo_t) + 1];
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// info may be NULL on Solaris (see #3790)
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memset(buf+1, 0, sizeof(siginfo_t));
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memcpy(buf+1, info, sizeof(siginfo_t));
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r = write(io_manager_control_fd, buf, sizeof(siginfo_t)+1);
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if (r == -1 && errno == EAGAIN)
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errorBelch("lost signal due to full pipe: %d\n", sig);
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// If the IO manager hasn't told us what the FD of the write end
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// of its pipe is, there's not much we can do here, so just ignore
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#else /* not THREADED_RTS */
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/* Can't call allocate from here. Probably can't call malloc
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either. However, we have to schedule a new thread somehow.
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It's probably ok to request a context switch and allow the
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scheduler to start the handler thread, but how do we
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communicate this to the scheduler?
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We need some kind of locking, but with low overhead (i.e. no
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blocking signals every time around the scheduler).
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Signal Handlers are atomic (i.e. they can't be interrupted), and
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we can make use of this. We just need to make sure the
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critical section of the scheduler can't be interrupted - the
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only way to do this is to block signals. However, we can lower
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the overhead by only blocking signals when there are any
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handlers to run, i.e. the set of pending handlers is
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/* We use a stack to store the pending signals. We can't
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dynamically grow this since we can't allocate any memory from
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within a signal handler.
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Hence unfortunately we have to bomb out if the buffer
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overflows. It might be acceptable to carry on in certain
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circumstances, depending on the signal.
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memcpy(next_pending_handler, info, sizeof(siginfo_t));
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next_pending_handler++;
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if (next_pending_handler == &pending_handler_buf[N_PENDING_HANDLERS]) {
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errorBelch("too many pending signals");
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stg_exit(EXIT_FAILURE);
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contextSwitchCapability(&MainCapability);
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#endif /* THREADED_RTS */
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/* -----------------------------------------------------------------------------
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* Blocking/Unblocking of the user signals
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* -------------------------------------------------------------------------- */
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static sigset_t userSignals;
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static sigset_t savedSignals;
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initUserSignals(void)
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sigemptyset(&userSignals);
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getStablePtr((StgPtr)&base_GHCziConcziSignal_runHandlers_closure);
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// needed to keep runHandler alive
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blockUserSignals(void)
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sigprocmask(SIG_BLOCK, &userSignals, &savedSignals);
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unblockUserSignals(void)
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sigprocmask(SIG_SETMASK, &savedSignals, NULL);
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anyUserHandlers(void)
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return n_haskell_handlers != 0;
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#if !defined(THREADED_RTS)
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awaitUserSignals(void)
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while (!signals_pending() && sched_state == SCHED_RUNNING) {
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/* -----------------------------------------------------------------------------
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* Install a Haskell signal handler.
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* We should really do this in Haskell in GHC.Conc, and share the
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* signal_handlers array with the one there.
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* -------------------------------------------------------------------------- */
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stg_sig_install(int sig, int spi, void *mask)
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sigset_t signals, osignals;
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struct sigaction action;
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// Block the signal until we figure out what to do
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// Count on this to fail if the signal number is invalid
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if (sig < 0 || sigemptyset(&signals) ||
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sigaddset(&signals, sig) || sigprocmask(SIG_BLOCK, &signals, &osignals)) {
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previous_spi = signal_handlers[sig];
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action.sa_handler = SIG_IGN;
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action.sa_handler = SIG_DFL;
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action.sa_flags |= SA_RESETHAND;
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action.sa_sigaction = generic_handler;
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action.sa_flags |= SA_SIGINFO;
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barf("stg_sig_install: bad spi");
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action.sa_mask = *(sigset_t *)mask;
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sigemptyset(&action.sa_mask);
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action.sa_flags |= sig == SIGCHLD && nocldstop ? SA_NOCLDSTOP : 0;
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if (sigaction(sig, &action, NULL))
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errorBelch("sigaction");
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signal_handlers[sig] = spi;
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sigaddset(&userSignals, sig);
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if (previous_spi != STG_SIG_HAN && previous_spi != STG_SIG_RST) {
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n_haskell_handlers++;
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sigdelset(&userSignals, sig);
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if (previous_spi == STG_SIG_HAN || previous_spi == STG_SIG_RST) {
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n_haskell_handlers--;
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if (sigprocmask(SIG_SETMASK, &osignals, NULL))
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errorBelch("sigprocmask");
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/* -----------------------------------------------------------------------------
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* Creating new threads for signal handlers.
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* -------------------------------------------------------------------------- */
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#if !defined(THREADED_RTS)
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startSignalHandlers(Capability *cap)
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while (next_pending_handler != pending_handler_buf) {
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next_pending_handler--;
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sig = next_pending_handler->si_signo;
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if (signal_handlers[sig] == STG_SIG_DFL) {
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continue; // handler has been changed.
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info = stgMallocBytes(sizeof(siginfo_t), "startSignalHandlers");
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// freed by runHandler
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memcpy(info, next_pending_handler, sizeof(siginfo_t));
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RtsFlags.GcFlags.initialStkSize,
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&base_GHCziConcziSignal_runHandlers_closure,
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rts_mkPtr(cap, info)),
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rts_mkInt(cap, info->si_signo))));
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unblockUserSignals();
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/* ----------------------------------------------------------------------------
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* Mark signal handlers during GC.
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* -------------------------------------------------------------------------- */
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markSignalHandlers (evac_fn evac STG_UNUSED, void *user STG_UNUSED)
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#else /* !RTS_USER_SIGNALS */
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stg_sig_install(StgInt sig STG_UNUSED,
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StgInt spi STG_UNUSED,
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void* mask STG_UNUSED)
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//barf("User signals not supported");
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#if defined(RTS_USER_SIGNALS)
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/* -----------------------------------------------------------------------------
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* We like to shutdown nicely after receiving a SIGINT, write out the
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* stats, write profiling info, close open files and flush buffers etc.
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* -------------------------------------------------------------------------- */
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shutdown_handler(int sig STG_UNUSED)
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// If we're already trying to interrupt the RTS, terminate with
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// extreme prejudice. So the first ^C tries to exit the program
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// cleanly, and the second one just kills it.
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if (sched_state >= SCHED_INTERRUPTING) {
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stg_exit(EXIT_INTERRUPTED);
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/* -----------------------------------------------------------------------------
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* An empty signal handler, currently used for SIGPIPE
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* -------------------------------------------------------------------------- */
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empty_handler (int sig STG_UNUSED)
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/* -----------------------------------------------------------------------------
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* Install default signal handlers.
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* The RTS installs a default signal handler for catching
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* SIGINT, so that we can perform an orderly shutdown.
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* Haskell code may install their own SIGINT handler, which is
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* fine, provided they're so kind as to put back the old one
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* when they de-install.
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* In addition to handling SIGINT, the RTS also handles SIGFPE
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* by ignoring it. Apparently IEEE requires floating-point
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* exceptions to be ignored by default, but alpha-dec-osf3
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* doesn't seem to do so.
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* -------------------------------------------------------------------------- */
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initDefaultHandlers(void)
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struct sigaction action,oact;
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// install the SIGINT handler
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action.sa_handler = shutdown_handler;
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sigemptyset(&action.sa_mask);
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if (sigaction(SIGINT, &action, &oact) != 0) {
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sysErrorBelch("warning: failed to install SIGINT handler");
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#if defined(HAVE_SIGINTERRUPT)
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siginterrupt(SIGINT, 1); // isn't this the default? --SDM
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// install the SIGFPE handler
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// In addition to handling SIGINT, also handle SIGFPE by ignoring it.
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// Apparently IEEE requires floating-point exceptions to be ignored by
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// default, but alpha-dec-osf3 doesn't seem to do so.
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// Commented out by SDM 2/7/2002: this causes an infinite loop on
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// some architectures when an integer division by zero occurs: we
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// don't recover from the floating point exception, and the
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// program just generates another one immediately.
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action.sa_handler = SIG_IGN;
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sigemptyset(&action.sa_mask);
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if (sigaction(SIGFPE, &action, &oact) != 0) {
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sysErrorBelch("warning: failed to install SIGFPE handler");
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#ifdef alpha_HOST_ARCH
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ieee_set_fp_control(0);
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// ignore SIGPIPE; see #1619
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// actually, we use an empty signal handler rather than SIG_IGN,
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// so that SIGPIPE gets reset to its default behaviour on exec.
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action.sa_handler = empty_handler;
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sigemptyset(&action.sa_mask);
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if (sigaction(SIGPIPE, &action, &oact) != 0) {
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sysErrorBelch("warning: failed to install SIGPIPE handler");
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resetDefaultHandlers(void)
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struct sigaction action;
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action.sa_handler = SIG_DFL;
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sigemptyset(&action.sa_mask);
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if (sigaction(SIGINT, &action, NULL) != 0) {
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sysErrorBelch("warning: failed to uninstall SIGINT handler");
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if (sigaction(SIGPIPE, &action, NULL) != 0) {
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sysErrorBelch("warning: failed to uninstall SIGPIPE handler");
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freeSignalHandlers(void) {
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if (signal_handlers != NULL) {
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stgFree(signal_handlers);
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#endif /* RTS_USER_SIGNALS */