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#include "private/pthread_support.h"
#if defined(GC_PTHREADS) && !defined(GC_WIN32_THREADS) && \
!defined(GC_DARWIN_THREADS)
#include <signal.h>
#include <semaphore.h>
#include <errno.h>
#include <unistd.h>
#include "atomic_ops.h"
#if DEBUG_THREADS
#ifndef NSIG
# if defined(MAXSIG)
# define NSIG (MAXSIG+1)
# elif defined(_NSIG)
# define NSIG _NSIG
# elif defined(__SIGRTMAX)
# define NSIG (__SIGRTMAX+1)
# else
--> please fix it
# endif
#endif
void GC_print_sig_mask()
{
sigset_t blocked;
int i;
if (pthread_sigmask(SIG_BLOCK, NULL, &blocked) != 0)
ABORT("pthread_sigmask");
GC_printf("Blocked: ");
for (i = 1; i < NSIG; i++) {
if (sigismember(&blocked, i)) { GC_printf("%d ", i); }
}
GC_printf("\n");
}
#endif
/* Remove the signals that we want to allow in thread stopping */
/* handler from a set. */
void GC_remove_allowed_signals(sigset_t *set)
{
if (sigdelset(set, SIGINT) != 0
|| sigdelset(set, SIGQUIT) != 0
|| sigdelset(set, SIGABRT) != 0
|| sigdelset(set, SIGTERM) != 0) {
ABORT("sigdelset() failed");
}
# ifdef MPROTECT_VDB
/* Handlers write to the thread structure, which is in the heap, */
/* and hence can trigger a protection fault. */
if (sigdelset(set, SIGSEGV) != 0
# ifdef SIGBUS
|| sigdelset(set, SIGBUS) != 0
# endif
) {
ABORT("sigdelset() failed");
}
# endif
}
static sigset_t suspend_handler_mask;
volatile AO_t GC_stop_count;
/* Incremented at the beginning of GC_stop_world. */
volatile AO_t GC_world_is_stopped = FALSE;
/* FALSE ==> it is safe for threads to restart, i.e. */
/* they will see another suspend signal before they */
/* are expected to stop (unless they have voluntarily */
/* stopped). */
#ifdef GC_OSF1_THREADS
GC_bool GC_retry_signals = TRUE;
#else
GC_bool GC_retry_signals = FALSE;
#endif
/*
* We use signals to stop threads during GC.
*
* Suspended threads wait in signal handler for SIG_THR_RESTART.
* That's more portable than semaphores or condition variables.
* (We do use sem_post from a signal handler, but that should be portable.)
*
* The thread suspension signal SIG_SUSPEND is now defined in gc_priv.h.
* Note that we can't just stop a thread; we need it to save its stack
* pointer(s) and acknowledge.
*/
#ifndef SIG_THR_RESTART
# if defined(GC_HPUX_THREADS) || defined(GC_OSF1_THREADS) || defined(GC_NETBSD_THREADS)
# ifdef _SIGRTMIN
# define SIG_THR_RESTART _SIGRTMIN + 5
# else
# define SIG_THR_RESTART SIGRTMIN + 5
# endif
# else
# define SIG_THR_RESTART SIGXCPU
# endif
#endif
sem_t GC_suspend_ack_sem;
#ifdef GC_NETBSD_THREADS
# define GC_NETBSD_THREADS_WORKAROUND
/* It seems to be necessary to wait until threads have restarted. */
/* But it is unclear why that is the case. */
sem_t GC_restart_ack_sem;
#endif
void GC_suspend_handler_inner(ptr_t sig_arg, void *context);
#if defined(IA64) || defined(HP_PA) || defined(M68K)
#ifdef SA_SIGINFO
void GC_suspend_handler(int sig, siginfo_t *info, void *context)
#else
void GC_suspend_handler(int sig)
#endif
{
int old_errno = errno;
GC_with_callee_saves_pushed(GC_suspend_handler_inner, (ptr_t)(word)sig);
errno = old_errno;
}
#else
/* We believe that in all other cases the full context is already */
/* in the signal handler frame. */
#ifdef SA_SIGINFO
void GC_suspend_handler(int sig, siginfo_t *info, void *context)
#else
void GC_suspend_handler(int sig)
#endif
{
int old_errno = errno;
# ifndef SA_SIGINFO
void *context = 0;
# endif
GC_suspend_handler_inner((ptr_t)(word)sig, context);
errno = old_errno;
}
#endif
void GC_suspend_handler_inner(ptr_t sig_arg, void *context)
{
int sig = (int)(word)sig_arg;
int dummy;
pthread_t my_thread = pthread_self();
GC_thread me;
# ifdef PARALLEL_MARK
word my_mark_no = GC_mark_no;
/* Marker can't proceed until we acknowledge. Thus this is */
/* guaranteed to be the mark_no correspending to our */
/* suspension, i.e. the marker can't have incremented it yet. */
# endif
AO_t my_stop_count = AO_load(&GC_stop_count);
if (sig != SIG_SUSPEND) ABORT("Bad signal in suspend_handler");
# if DEBUG_THREADS
GC_printf("Suspending 0x%x\n", (unsigned)my_thread);
# endif
me = GC_lookup_thread(my_thread);
/* The lookup here is safe, since I'm doing this on behalf */
/* of a thread which holds the allocation lock in order */
/* to stop the world. Thus concurrent modification of the */
/* data structure is impossible. */
if (me -> stop_info.last_stop_count == my_stop_count) {
/* Duplicate signal. OK if we are retrying. */
if (!GC_retry_signals) {
WARN("Duplicate suspend signal in thread %lx\n",
pthread_self());
}
return;
}
# ifdef SPARC
me -> stop_info.stack_ptr = GC_save_regs_in_stack();
# else
me -> stop_info.stack_ptr = (ptr_t)(&dummy);
# endif
# ifdef IA64
me -> backing_store_ptr = GC_save_regs_in_stack();
# endif
/* Tell the thread that wants to stop the world that this */
/* thread has been stopped. Note that sem_post() is */
/* the only async-signal-safe primitive in LinuxThreads. */
sem_post(&GC_suspend_ack_sem);
me -> stop_info.last_stop_count = my_stop_count;
/* Wait until that thread tells us to restart by sending */
/* this thread a SIG_THR_RESTART signal. */
/* SIG_THR_RESTART should be masked at this point. Thus there */
/* is no race. */
/* We do not continue until we receive a SIG_THR_RESTART, */
/* but we do not take that as authoritative. (We may be */
/* accidentally restarted by one of the user signals we */
/* don't block.) After we receive the signal, we use a */
/* primitive and expensive mechanism to wait until it's */
/* really safe to proceed. Under normal circumstances, */
/* this code should not be executed. */
do {
sigsuspend (&suspend_handler_mask);
} while (AO_load_acquire(&GC_world_is_stopped)
&& AO_load(&GC_stop_count) == my_stop_count);
/* If the RESTART signal gets lost, we can still lose. That should be */
/* less likely than losing the SUSPEND signal, since we don't do much */
/* between the sem_post and sigsuspend. */
/* We'd need more handshaking to work around that. */
/* Simply dropping the sigsuspend call should be safe, but is unlikely */
/* to be efficient. */
# if DEBUG_THREADS
GC_printf("Continuing 0x%x\n", (unsigned)my_thread);
# endif
}
void GC_restart_handler(int sig)
{
pthread_t my_thread = pthread_self();
GC_thread me;
if (sig != SIG_THR_RESTART) ABORT("Bad signal in suspend_handler");
# ifdef GC_NETBSD_THREADS_WORKAROUND
sem_post(&GC_restart_ack_sem);
# endif
/*
** Note: even if we don't do anything useful here,
** it would still be necessary to have a signal handler,
** rather than ignoring the signals, otherwise
** the signals will not be delivered at all, and
** will thus not interrupt the sigsuspend() above.
*/
# if DEBUG_THREADS
GC_printf("In GC_restart_handler for 0x%x\n", (unsigned)pthread_self());
# endif
}
# ifdef IA64
# define IF_IA64(x) x
# else
# define IF_IA64(x)
# endif
/* We hold allocation lock. Should do exactly the right thing if the */
/* world is stopped. Should not fail if it isn't. */
void GC_push_all_stacks()
{
GC_bool found_me = FALSE;
size_t nthreads = 0;
int i;
GC_thread p;
ptr_t lo, hi;
/* On IA64, we also need to scan the register backing store. */
IF_IA64(ptr_t bs_lo; ptr_t bs_hi;)
pthread_t me = pthread_self();
if (!GC_thr_initialized) GC_thr_init();
# if DEBUG_THREADS
GC_printf("Pushing stacks from thread 0x%x\n", (unsigned) me);
# endif
for (i = 0; i < THREAD_TABLE_SZ; i++) {
for (p = GC_threads[i]; p != 0; p = p -> next) {
if (p -> flags & FINISHED) continue;
++nthreads;
if (THREAD_EQUAL(p -> id, me)) {
# ifdef SPARC
lo = (ptr_t)GC_save_regs_in_stack();
# else
lo = GC_approx_sp();
# endif
found_me = TRUE;
IF_IA64(bs_hi = (ptr_t)GC_save_regs_in_stack();)
} else {
lo = p -> stop_info.stack_ptr;
IF_IA64(bs_hi = p -> backing_store_ptr;)
}
if ((p -> flags & MAIN_THREAD) == 0) {
hi = p -> stack_end;
IF_IA64(bs_lo = p -> backing_store_end);
} else {
/* The original stack. */
hi = GC_stackbottom;
IF_IA64(bs_lo = BACKING_STORE_BASE;)
}
# if DEBUG_THREADS
GC_printf("Stack for thread 0x%x = [%p,%p)\n",
(unsigned)(p -> id), lo, hi);
# endif
if (0 == lo) ABORT("GC_push_all_stacks: sp not set!\n");
# ifdef STACK_GROWS_UP
/* We got them backwards! */
GC_push_all_stack(hi, lo);
# else
GC_push_all_stack(lo, hi);
# endif
# ifdef IA64
# if DEBUG_THREADS
GC_printf("Reg stack for thread 0x%x = [%lx,%lx)\n",
(unsigned)p -> id, bs_lo, bs_hi);
# endif
if (THREAD_EQUAL(p -> id, me)) {
/* FIXME: This may add an unbounded number of entries, */
/* and hence overflow the mark stack, which is bad. */
GC_push_all_eager(bs_lo, bs_hi);
} else {
GC_push_all_stack(bs_lo, bs_hi);
}
# endif
}
}
if (GC_print_stats == VERBOSE) {
GC_log_printf("Pushed %d thread stacks\n", nthreads);
}
if (!found_me && !GC_in_thread_creation)
ABORT("Collecting from unknown thread.");
}
/* There seems to be a very rare thread stopping problem. To help us */
/* debug that, we save the ids of the stopping thread. */
pthread_t GC_stopping_thread;
int GC_stopping_pid;
/* We hold the allocation lock. Suspend all threads that might */
/* still be running. Return the number of suspend signals that */
/* were sent. */
int GC_suspend_all()
{
int n_live_threads = 0;
int i;
GC_thread p;
int result;
pthread_t my_thread = pthread_self();
GC_stopping_thread = my_thread; /* debugging only. */
GC_stopping_pid = getpid(); /* debugging only. */
for (i = 0; i < THREAD_TABLE_SZ; i++) {
for (p = GC_threads[i]; p != 0; p = p -> next) {
if (!THREAD_EQUAL(p -> id, my_thread)) {
if (p -> flags & FINISHED) continue;
if (p -> stop_info.last_stop_count == GC_stop_count) continue;
if (p -> thread_blocked) /* Will wait */ continue;
n_live_threads++;
# if DEBUG_THREADS
GC_printf("Sending suspend signal to 0x%x\n",
(unsigned)(p -> id));
# endif
result = pthread_kill(p -> id, SIG_SUSPEND);
switch(result) {
case ESRCH:
/* Not really there anymore. Possible? */
n_live_threads--;
break;
case 0:
break;
default:
ABORT("pthread_kill failed");
}
}
}
}
return n_live_threads;
}
void GC_stop_world()
{
int i;
int n_live_threads;
int code;
GC_ASSERT(I_HOLD_LOCK());
# if DEBUG_THREADS
GC_printf("Stopping the world from 0x%x\n", (unsigned)pthread_self());
# endif
/* Make sure all free list construction has stopped before we start. */
/* No new construction can start, since free list construction is */
/* required to acquire and release the GC lock before it starts, */
/* and we have the lock. */
# ifdef PARALLEL_MARK
GC_acquire_mark_lock();
GC_ASSERT(GC_fl_builder_count == 0);
/* We should have previously waited for it to become zero. */
# endif /* PARALLEL_MARK */
AO_store(&GC_stop_count, GC_stop_count+1);
/* Only concurrent reads are possible. */
AO_store_release(&GC_world_is_stopped, TRUE);
n_live_threads = GC_suspend_all();
if (GC_retry_signals) {
unsigned long wait_usecs = 0; /* Total wait since retry. */
# define WAIT_UNIT 3000
# define RETRY_INTERVAL 100000
for (;;) {
int ack_count;
sem_getvalue(&GC_suspend_ack_sem, &ack_count);
if (ack_count == n_live_threads) break;
if (wait_usecs > RETRY_INTERVAL) {
int newly_sent = GC_suspend_all();
if (GC_print_stats) {
GC_log_printf("Resent %d signals after timeout\n",
newly_sent);
}
sem_getvalue(&GC_suspend_ack_sem, &ack_count);
if (newly_sent < n_live_threads - ack_count) {
WARN("Lost some threads during GC_stop_world?!\n",0);
n_live_threads = ack_count + newly_sent;
}
wait_usecs = 0;
}
usleep(WAIT_UNIT);
wait_usecs += WAIT_UNIT;
}
}
for (i = 0; i < n_live_threads; i++) {
retry:
if (0 != (code = sem_wait(&GC_suspend_ack_sem))) {
/* On Linux, sem_wait is documented to always return zero.*/
/* But the documentation appears to be incorrect. */
if (errno == EINTR) {
/* Seems to happen with some versions of gdb. */
goto retry;
}
ABORT("sem_wait for handler failed");
}
}
# ifdef PARALLEL_MARK
GC_release_mark_lock();
# endif
#if DEBUG_THREADS
GC_printf("World stopped from 0x%x\n", (unsigned)pthread_self());
#endif
GC_stopping_thread = 0; /* debugging only */
}
/* Caller holds allocation lock, and has held it continuously since */
/* the world stopped. */
void GC_start_world()
{
pthread_t my_thread = pthread_self();
register int i;
register GC_thread p;
register int n_live_threads = 0;
register int result;
# ifdef GC_NETBSD_THREADS_WORKAROUND
int code;
# endif
# if DEBUG_THREADS
GC_printf("World starting\n");
# endif
AO_store(&GC_world_is_stopped, FALSE);
for (i = 0; i < THREAD_TABLE_SZ; i++) {
for (p = GC_threads[i]; p != 0; p = p -> next) {
if (!THREAD_EQUAL(p -> id, my_thread)) {
if (p -> flags & FINISHED) continue;
if (p -> thread_blocked) continue;
n_live_threads++;
#if DEBUG_THREADS
GC_printf("Sending restart signal to 0x%x\n",
(unsigned)(p -> id));
#endif
result = pthread_kill(p -> id, SIG_THR_RESTART);
switch(result) {
case ESRCH:
/* Not really there anymore. Possible? */
n_live_threads--;
break;
case 0:
break;
default:
ABORT("pthread_kill failed");
}
}
}
}
# ifdef GC_NETBSD_THREADS_WORKAROUND
for (i = 0; i < n_live_threads; i++)
while (0 != (code = sem_wait(&GC_restart_ack_sem)))
if (errno != EINTR) {
GC_err_printf("sem_wait() returned %d\n",
code);
ABORT("sem_wait() for restart handler failed");
}
# endif
# if DEBUG_THREADS
GC_printf("World started\n");
# endif
}
void GC_stop_init() {
struct sigaction act;
if (sem_init(&GC_suspend_ack_sem, 0, 0) != 0)
ABORT("sem_init failed");
# ifdef GC_NETBSD_THREADS_WORKAROUND
if (sem_init(&GC_restart_ack_sem, 0, 0) != 0)
ABORT("sem_init failed");
# endif
act.sa_flags = SA_RESTART
# ifdef SA_SIGINFO
| SA_SIGINFO
# endif
;
if (sigfillset(&act.sa_mask) != 0) {
ABORT("sigfillset() failed");
}
GC_remove_allowed_signals(&act.sa_mask);
/* SIG_THR_RESTART is set in the resulting mask. */
/* It is unmasked by the handler when necessary. */
# ifdef SA_SIGINFO
act.sa_sigaction = GC_suspend_handler;
# else
act.sa_handler = GC_suspend_handler;
# endif
if (sigaction(SIG_SUSPEND, &act, NULL) != 0) {
ABORT("Cannot set SIG_SUSPEND handler");
}
# ifdef SA_SIGINFO
act.sa_flags &= ~ SA_SIGINFO;
# endif
act.sa_handler = GC_restart_handler;
if (sigaction(SIG_THR_RESTART, &act, NULL) != 0) {
ABORT("Cannot set SIG_THR_RESTART handler");
}
/* Inititialize suspend_handler_mask. It excludes SIG_THR_RESTART. */
if (sigfillset(&suspend_handler_mask) != 0) ABORT("sigfillset() failed");
GC_remove_allowed_signals(&suspend_handler_mask);
if (sigdelset(&suspend_handler_mask, SIG_THR_RESTART) != 0)
ABORT("sigdelset() failed");
/* Check for GC_RETRY_SIGNALS. */
if (0 != GETENV("GC_RETRY_SIGNALS")) {
GC_retry_signals = TRUE;
}
if (0 != GETENV("GC_NO_RETRY_SIGNALS")) {
GC_retry_signals = FALSE;
}
if (GC_print_stats && GC_retry_signals) {
GC_log_printf("Will retry suspend signal if necessary.\n");
}
}
#endif