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Implement KillHandle::kill() and friends (unkillable, atomically). Close #6377.

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This commit is contained in:
Ben Blum 2013-07-08 13:48:57 -04:00
parent 2a99320583
commit 629f6e8d68
2 changed files with 227 additions and 37 deletions
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152
src/libstd/rt/kill.rs
View File

@ -10,15 +10,38 @@
//! Task death: asynchronous killing, linked failure, exit code propagation.
use cast;
use cell::Cell;
use option::{Option, Some, None};
use prelude::*;
use rt::task::Task;
use unstable::atomics::{AtomicUint, SeqCst};
use unstable::sync::{UnsafeAtomicRcBox, LittleLock};
use util;
static KILLED_MSG: &'static str = "killed by linked failure";
// State values for the 'killed' and 'unkillable' atomic flags below.
static KILL_RUNNING: uint = 0;
static KILL_KILLED: uint = 1;
static KILL_UNKILLABLE: uint = 2;
// FIXME(#7544)(bblum): think about the cache efficiency of this
struct KillHandleInner {
// ((more fields to be added in a future commit))
// Is the task running, blocked, or killed? Possible values:
// * KILL_RUNNING - Not unkillable, no kill pending.
// * KILL_KILLED - Kill pending.
// * <ptr> - A transmuted blocked ~Task pointer.
// This flag is refcounted because it may also be referenced by a blocking
// concurrency primitive, used to wake the task normally, whose reference
// may outlive the handle's if the task is killed.
killed: UnsafeAtomicRcBox<AtomicUint>,
// Has the task deferred kill signals? This flag guards the above one.
// Possible values:
// * KILL_RUNNING - Not unkillable, no kill pending.
// * KILL_KILLED - Kill pending.
// * KILL_UNKILLABLE - Kill signals deferred.
unkillable: AtomicUint,
// Shared state between task and children for exit code propagation. These
// are here so we can re-use the kill handle to implement watched children
@ -47,13 +70,18 @@ pub struct Death {
// Action to be done with the exit code. If set, also makes the task wait
// until all its watched children exit before collecting the status.
on_exit: Option<~fn(bool)>,
// nesting level counter for task::unkillable calls (0 == killable).
unkillable: int,
// nesting level counter for task::atomically calls (0 == can yield).
wont_sleep: int,
}
impl KillHandle {
pub fn new() -> KillHandle {
KillHandle(UnsafeAtomicRcBox::new(KillHandleInner {
// Linked failure fields
// ((none yet))
killed: UnsafeAtomicRcBox::new(AtomicUint::new(KILL_RUNNING)),
unkillable: AtomicUint::new(KILL_RUNNING),
// Exit code propagation fields
any_child_failed: false,
child_tombstones: None,
@ -61,6 +89,54 @@ impl KillHandle {
}))
}
// Will begin unwinding if a kill signal was received, unless already_failing.
// This can't be used recursively, because a task which sees a KILLED
// signal must fail immediately, which an already-unkillable task can't do.
#[inline]
pub fn inhibit_kill(&mut self, already_failing: bool) {
let inner = unsafe { &mut *self.get() };
// Expect flag to contain RUNNING. If KILLED, it should stay KILLED.
// FIXME(#7544)(bblum): is it really necessary to prohibit double kill?
match inner.unkillable.compare_and_swap(KILL_RUNNING, KILL_UNKILLABLE, SeqCst) {
KILL_RUNNING => { }, // normal case
KILL_KILLED => if !already_failing { fail!(KILLED_MSG) },
_ => rtabort!("inhibit_kill: task already unkillable"),
}
}
// Will begin unwinding if a kill signal was received, unless already_failing.
#[inline]
pub fn allow_kill(&mut self, already_failing: bool) {
let inner = unsafe { &mut *self.get() };
// Expect flag to contain UNKILLABLE. If KILLED, it should stay KILLED.
// FIXME(#7544)(bblum): is it really necessary to prohibit double kill?
match inner.unkillable.compare_and_swap(KILL_UNKILLABLE, KILL_RUNNING, SeqCst) {
KILL_UNKILLABLE => { }, // normal case
KILL_KILLED => if !already_failing { fail!(KILLED_MSG) },
_ => rtabort!("allow_kill: task already killable"),
}
}
// Send a kill signal to the handle's owning task. Returns the task itself
// if it was blocked and needs punted awake. To be called by other tasks.
pub fn kill(&mut self) -> Option<~Task> {
let inner = unsafe { &mut *self.get() };
if inner.unkillable.swap(KILL_KILLED, SeqCst) == KILL_RUNNING {
// Got in. Allowed to try to punt the task awake.
let flag = unsafe { &mut *inner.killed.get() };
match flag.swap(KILL_KILLED, SeqCst) {
// Task either not blocked or already taken care of.
KILL_RUNNING | KILL_KILLED => None,
// Got ownership of the blocked task.
task_ptr => Some(unsafe { cast::transmute(task_ptr) }),
}
} else {
// Otherwise it was either unkillable or already killed. Somebody
// else was here first who will deal with the kill signal.
None
}
}
pub fn notify_immediate_failure(&mut self) {
// A benign data race may happen here if there are failing sibling
// tasks that were also spawned-watched. The refcount's write barriers
@ -123,6 +199,7 @@ impl KillHandle {
}
// NB: Takes a pthread mutex -- 'blk' not allowed to reschedule.
#[inline]
fn add_lazy_tombstone(parent: &mut KillHandle,
blk: &fn(Option<~fn() -> bool>) -> ~fn() -> bool) {
@ -144,6 +221,8 @@ impl Death {
kill_handle: Some(KillHandle::new()),
watching_parent: None,
on_exit: None,
unkillable: 0,
wont_sleep: 0,
}
}
@ -153,11 +232,22 @@ impl Death {
kill_handle: Some(KillHandle::new()),
watching_parent: self.kill_handle.clone(),
on_exit: None,
unkillable: 0,
wont_sleep: 0,
}
}
/// Collect failure exit codes from children and propagate them to a parent.
pub fn collect_failure(&mut self, mut success: bool) {
// This may run after the task has already failed, so even though the
// task appears to need to be killed, the scheduler should not fail us
// when we block to unwrap.
// (XXX: Another less-elegant reason for doing this is so that the use
// of the LittleLock in reparent_children_to doesn't need to access the
// unkillable flag in the kill_handle, since we'll have removed it.)
rtassert!(self.unkillable == 0);
self.unkillable = 1;
// Step 1. Decide if we need to collect child failures synchronously.
do self.on_exit.take_map |on_exit| {
if success {
@ -191,6 +281,64 @@ impl Death {
parent_handle.notify_immediate_failure();
}
};
// Can't use allow_kill directly; that would require the kill handle.
rtassert!(self.unkillable == 1);
self.unkillable = 0;
}
/// Enter a possibly-nested unkillable section of code.
/// All calls must be paired with a subsequent call to allow_kill.
#[inline]
pub fn inhibit_kill(&mut self, already_failing: bool) {
if self.unkillable == 0 {
rtassert!(self.kill_handle.is_some());
self.kill_handle.get_mut_ref().inhibit_kill(already_failing);
}
self.unkillable += 1;
}
/// Exit a possibly-nested unkillable section of code.
/// All calls must be paired with a preceding call to inhibit_kill.
#[inline]
pub fn allow_kill(&mut self, already_failing: bool) {
rtassert!(self.unkillable != 0);
self.unkillable -= 1;
if self.unkillable == 0 {
rtassert!(self.kill_handle.is_some());
self.kill_handle.get_mut_ref().allow_kill(already_failing);
}
}
/// Enter a possibly-nested "atomic" section of code. Just for assertions.
/// All calls must be paired with a subsequent call to allow_yield.
#[inline]
pub fn inhibit_yield(&mut self) {
self.wont_sleep += 1;
}
/// Exit a possibly-nested "atomic" section of code. Just for assertions.
/// All calls must be paired with a preceding call to inhibit_yield.
#[inline]
pub fn allow_yield(&mut self) {
rtassert!(self.wont_sleep != 0);
self.wont_sleep -= 1;
}
/// Ensure that the task is allowed to become descheduled.
#[inline]
pub fn assert_may_sleep(&self) {
if self.wont_sleep != 0 {
rtabort!("illegal atomic-sleep: can't deschedule inside atomically()");
}
}
}
impl Drop for Death {
fn drop(&self) {
// Mustn't be in an atomic or unkillable section at task death.
rtassert!(self.unkillable == 0);
rtassert!(self.wont_sleep == 0);
}
}

66
src/libstd/task/mod.rs
View File

@ -42,7 +42,8 @@ use cmp::Eq;
use comm::{stream, Chan, GenericChan, GenericPort, Port};
use result::Result;
use result;
use rt::{context, OldTaskContext};
use rt::{context, OldTaskContext, TaskContext};
use rt::local::Local;
use task::rt::{task_id, sched_id};
use unstable::finally::Finally;
use util::replace;
@ -526,8 +527,6 @@ pub fn yield() {
pub fn failing() -> bool {
//! True if the running task has failed
use rt::{context, OldTaskContext};
use rt::local::Local;
use rt::task::Task;
match context() {
@ -572,7 +571,10 @@ pub fn get_scheduler() -> Scheduler {
* ~~~
*/
pub unsafe fn unkillable<U>(f: &fn() -> U) -> U {
if context() == OldTaskContext {
use rt::task::Task;
match context() {
OldTaskContext => {
let t = rt::rust_get_task();
do (|| {
rt::rust_task_inhibit_kill(t);
@ -580,15 +582,29 @@ pub unsafe fn unkillable<U>(f: &fn() -> U) -> U {
}).finally {
rt::rust_task_allow_kill(t);
}
} else {
// FIXME #6377
}
TaskContext => {
// The inhibits/allows might fail and need to borrow the task.
let t = Local::unsafe_borrow::<Task>();
do (|| {
(*t).death.inhibit_kill((*t).unwinder.unwinding);
f()
}).finally {
(*t).death.allow_kill((*t).unwinder.unwinding);
}
}
// FIXME(#3095): This should be an rtabort as soon as the scheduler
// no longer uses a workqueue implemented with an Exclusive.
_ => f()
}
}
/// The inverse of unkillable. Only ever to be used nested in unkillable().
pub unsafe fn rekillable<U>(f: &fn() -> U) -> U {
if context() == OldTaskContext {
use rt::task::Task;
match context() {
OldTaskContext => {
let t = rt::rust_get_task();
do (|| {
rt::rust_task_allow_kill(t);
@ -596,9 +612,18 @@ pub unsafe fn rekillable<U>(f: &fn() -> U) -> U {
}).finally {
rt::rust_task_inhibit_kill(t);
}
} else {
// FIXME #6377
}
TaskContext => {
let t = Local::unsafe_borrow::<Task>();
do (|| {
(*t).death.allow_kill((*t).unwinder.unwinding);
f()
}).finally {
(*t).death.inhibit_kill((*t).unwinder.unwinding);
}
}
// FIXME(#3095): As in unkillable().
_ => f()
}
}
@ -607,7 +632,10 @@ pub unsafe fn rekillable<U>(f: &fn() -> U) -> U {
* For use with exclusive ARCs, which use pthread mutexes directly.
*/
pub unsafe fn atomically<U>(f: &fn() -> U) -> U {
if context() == OldTaskContext {
use rt::task::Task;
match context() {
OldTaskContext => {
let t = rt::rust_get_task();
do (|| {
rt::rust_task_inhibit_kill(t);
@ -617,9 +645,23 @@ pub unsafe fn atomically<U>(f: &fn() -> U) -> U {
rt::rust_task_allow_yield(t);
rt::rust_task_allow_kill(t);
}
} else {
// FIXME #6377
}
TaskContext => {
let t = Local::unsafe_borrow::<Task>();
do (|| {
// It's important to inhibit kill after inhibiting yield, because
// inhibit-kill might fail if we were already killed, and the
// inhibit-yield must happen to match the finally's allow-yield.
(*t).death.inhibit_yield();
(*t).death.inhibit_kill((*t).unwinder.unwinding);
f()
}).finally {
(*t).death.allow_kill((*t).unwinder.unwinding);
(*t).death.allow_yield();
}
}
// FIXME(#3095): As in unkillable().
_ => f()
}
}