panicking::rust_panic_without_hook(payload)
}
+/// Make all future panics abort directly without running the panic hook or unwinding.
+///
+/// There is no way to undo this; the effect lasts until the process exits or
+/// execs (or the equivalent).
+///
+/// # Use after fork
+///
+/// This function is particularly useful for calling after `libc::fork`. After `fork`, in a
+/// multithreaded program it is (on many platforms) not safe to call the allocator. It is also
+/// generally highly undesirable for an unwind to unwind past the `fork`, because that results in
+/// the unwind propagating to code that was only ever expecting to run in the parent.
+///
+/// `panic::always_abort()` helps avoid both of these. It directly avoids any further unwinding,
+/// and if there is a panic, the abort will occur without allocating provided that the arguments to
+/// panic can be formatted without allocating.
+///
+/// Examples
+///
+/// ```no_run
+/// #![feature(panic_always_abort)]
+/// use std::panic;
+///
+/// panic::always_abort();
+///
+/// let _ = panic::catch_unwind(|| {
+/// panic!("inside the catch");
+/// });
+///
+/// // We will have aborted already, due to the panic.
+/// unreachable!();
+/// ```
+#[unstable(feature = "panic_always_abort", issue = "84438")]
+pub fn always_abort() {
+ crate::panicking::panic_count::set_always_abort();
+}
+
#[cfg(test)]
mod tests;
fn default_hook(info: &PanicInfo<'_>) {
// If this is a double panic, make sure that we print a backtrace
// for this panic. Otherwise only print it if logging is enabled.
- let backtrace_env = if panic_count::get() >= 2 {
+ let backtrace_env = if panic_count::get_count() >= 2 {
RustBacktrace::Print(crate::backtrace_rs::PrintFmt::Full)
} else {
backtrace::rust_backtrace_env()
use crate::cell::Cell;
use crate::sync::atomic::{AtomicUsize, Ordering};
+ pub const ALWAYS_ABORT_FLAG: usize = 1 << (usize::BITS - 1);
+
// Panic count for the current thread.
thread_local! { static LOCAL_PANIC_COUNT: Cell<usize> = Cell::new(0) }
// thread, if that thread currently views `GLOBAL_PANIC_COUNT` as being zero,
// then `LOCAL_PANIC_COUNT` in that thread is zero. This invariant holds before
// and after increase and decrease, but not necessarily during their execution.
+ //
+ // Additionally, the top bit of GLOBAL_PANIC_COUNT (GLOBAL_ALWAYS_ABORT_FLAG)
+ // records whether panic::always_abort() has been called. This can only be
+ // set, never cleared.
+ //
+ // This could be viewed as a struct containing a single bit and an n-1-bit
+ // value, but if we wrote it like that it would be more than a single word,
+ // and even a newtype around usize would be clumsy because we need atomics.
+ // But we use such a tuple for the return type of increase().
+ //
+ // Stealing a bit is fine because it just amounts to assuming that each
+ // panicking thread consumes at least 2 bytes of address space.
static GLOBAL_PANIC_COUNT: AtomicUsize = AtomicUsize::new(0);
- pub fn increase() -> usize {
- GLOBAL_PANIC_COUNT.fetch_add(1, Ordering::Relaxed);
- LOCAL_PANIC_COUNT.with(|c| {
- let next = c.get() + 1;
- c.set(next);
- next
- })
+ pub fn increase() -> (bool, usize) {
+ (
+ GLOBAL_PANIC_COUNT.fetch_add(1, Ordering::Acquire) & ALWAYS_ABORT_FLAG != 0,
+ LOCAL_PANIC_COUNT.with(|c| {
+ let next = c.get() + 1;
+ c.set(next);
+ next
+ }),
+ )
}
pub fn decrease() {
});
}
- pub fn get() -> usize {
+ pub fn set_always_abort() {
+ GLOBAL_PANIC_COUNT.fetch_or(ALWAYS_ABORT_FLAG, Ordering::Release);
+ }
+
+ // Disregards ALWAYS_ABORT_FLAG
+ pub fn get_count() -> usize {
LOCAL_PANIC_COUNT.with(|c| c.get())
}
+ // Disregards ALWAYS_ABORT_FLAG
#[inline]
- pub fn is_zero() -> bool {
- if GLOBAL_PANIC_COUNT.load(Ordering::Relaxed) == 0 {
+ pub fn count_is_zero() -> bool {
+ if GLOBAL_PANIC_COUNT.load(Ordering::Relaxed) & !ALWAYS_ABORT_FLAG == 0 {
// Fast path: if `GLOBAL_PANIC_COUNT` is zero, all threads
// (including the current one) will have `LOCAL_PANIC_COUNT`
// equal to zero, so TLS access can be avoided.
/// Determines whether the current thread is unwinding because of panic.
#[inline]
pub fn panicking() -> bool {
- !panic_count::is_zero()
+ !panic_count::count_is_zero()
}
/// The entry point for panicking with a formatted message.
message: Option<&fmt::Arguments<'_>>,
location: &Location<'_>,
) -> ! {
- let panics = panic_count::increase();
+ let (must_abort, panics) = panic_count::increase();
// If this is the third nested call (e.g., panics == 2, this is 0-indexed),
// the panic hook probably triggered the last panic, otherwise the
// double-panic check would have aborted the process. In this case abort the
// process real quickly as we don't want to try calling it again as it'll
// probably just panic again.
- if panics > 2 {
- util::dumb_print(format_args!("thread panicked while processing panic. aborting.\n"));
+ if must_abort || panics > 2 {
+ if panics > 2 {
+ // Don't try to print the message in this case
+ // - perhaps that is causing the recursive panics.
+ util::dumb_print(format_args!("thread panicked while processing panic. aborting.\n"));
+ } else {
+ // Unfortunately, this does not print a backtrace, because creating
+ // a `Backtrace` will allocate, which we must to avoid here.
+ let panicinfo = PanicInfo::internal_constructor(message, location);
+ util::dumb_print(format_args!(
+ "{}\npanicked after panic::always_abort(), aborting.\n",
+ panicinfo
+ ));
+ }
intrinsics::abort()
}