[ruby-core:93652] [Ruby master Bug#15992] An exception breaks monitor state and cause deadlock

[ruby-core:93652] [Ruby master Bug#15992] An exception breaks monitor state and cause deadlock

[naruse]

Issue #15992 has been reported by naruse (Yui NARUSE).

----------------------------------------
Bug #15992: An exception breaks monitor state and cause deadlock
https://bugs.ruby-lang.org/issues/15992

* Author: naruse (Yui NARUSE)
* Status: Open
* Priority: Normal
* Assignee: 
* Target version: 
* ruby -v: 
* Backport: 2.5: REQUIRED, 2.6: REQUIRED
----------------------------------------
lib/monitor.rb provides Monitor.
But its state handling is weak for interrupts caused by Thread.kill for example timeout libraries.

Timeout exception may happen everywhere. If it raised when the thread is executing

```ruby
  def mon_exit
    mon_check_owner
    @mon_count -=1
    if @mon_count == 0
      @mon_owner = nil
      # HERE!!!
      @mon_mutex.unlock
    end
  end
``` 

It breaks the state of the monitor and it causes deadlock.



-- 
https://bugs.ruby-lang.org/

[ruby-core:94407] [Ruby master Bug#15992] An exception breaks monitor state and cause deadlock

[nagachika00]

Issue #15992 has been updated by nagachika (Tomoyuki Chikanaga).

Backport changed from 2.5: REQUIRED, 2.6: REQUIRED to 2.5: REQUIRED, 2.6: DONE

ruby_2_6 r67742 merged revision(s) f91879a7b548284c93743168acfd11e3d2aeefac.

----------------------------------------
Bug #15992: An exception breaks monitor state and cause deadlock
https://bugs.ruby-lang.org/issues/15992#change-80827

* Author: naruse (Yui NARUSE)
* Status: Closed
* Priority: Normal
* Assignee: 
* Target version: 
* ruby -v: 
* Backport: 2.5: REQUIRED, 2.6: DONE
----------------------------------------
lib/monitor.rb provides Monitor.
But its state handling is weak for interrupts caused by Thread.kill for example timeout libraries.

Timeout exception may happen everywhere. If it raised when the thread is executing

```ruby
  def mon_exit
    mon_check_owner
    @mon_count -=1
    if @mon_count == 0
      @mon_owner = nil
      # HERE!!!
      @mon_mutex.unlock
    end
  end
``` 

It breaks the state of the monitor and it causes deadlock.



-- 
https://bugs.ruby-lang.org/

[ruby-core:94456] [Ruby master Bug#15992] An exception breaks monitor state and cause deadlock

[nagachika00]

Issue #15992 has been updated by nagachika (Tomoyuki Chikanaga).

Backport changed from 2.5: REQUIRED, 2.6: DONE to 2.5: REQUIRED, 2.6: REQUIRED

9557069299ac3b96691040a541afa65761a724ad is a follow up commit to ease memory consumption impact of f91879a7b548284c93743168acfd11e3d2aeefac. I think it should be backported too.

----------------------------------------
Bug #15992: An exception breaks monitor state and cause deadlock
https://bugs.ruby-lang.org/issues/15992#change-80887

* Author: naruse (Yui NARUSE)
* Status: Closed
* Priority: Normal
* Assignee: 
* Target version: 
* ruby -v: 
* Backport: 2.5: REQUIRED, 2.6: REQUIRED
----------------------------------------
lib/monitor.rb provides Monitor.
But its state handling is weak for interrupts caused by Thread.kill for example timeout libraries.

Timeout exception may happen everywhere. If it raised when the thread is executing

```ruby
  def mon_exit
    mon_check_owner
    @mon_count -=1
    if @mon_count == 0
      @mon_owner = nil
      # HERE!!!
      @mon_mutex.unlock
    end
  end
``` 

It breaks the state of the monitor and it causes deadlock.



-- 
https://bugs.ruby-lang.org/

[ruby-core:94478] [Ruby master Bug#15992] An exception breaks monitor state and cause deadlock

[nagachika00]

Issue #15992 has been updated by nagachika (Tomoyuki Chikanaga).

Backport changed from 2.5: REQUIRED, 2.6: REQUIRED to 2.5: REQUIRED, 2.6: DONE

ruby_2_6 r67749 merged revision(s) 9557069299ac3b96691040a541afa65761a724ad.

----------------------------------------
Bug #15992: An exception breaks monitor state and cause deadlock
https://bugs.ruby-lang.org/issues/15992#change-80913

* Author: naruse (Yui NARUSE)
* Status: Closed
* Priority: Normal
* Assignee: 
* Target version: 
* ruby -v: 
* Backport: 2.5: REQUIRED, 2.6: DONE
----------------------------------------
lib/monitor.rb provides Monitor.
But its state handling is weak for interrupts caused by Thread.kill for example timeout libraries.

Timeout exception may happen everywhere. If it raised when the thread is executing

```ruby
  def mon_exit
    mon_check_owner
    @mon_count -=1
    if @mon_count == 0
      @mon_owner = nil
      # HERE!!!
      @mon_mutex.unlock
    end
  end
``` 

It breaks the state of the monitor and it causes deadlock.



-- 
https://bugs.ruby-lang.org/

[ruby-core:94583] [Ruby master Bug#15992] An exception breaks monitor state and cause deadlock

[usa]

Issue #15992 has been updated by usa (Usaku NAKAMURA).

Backport changed from 2.5: REQUIRED, 2.6: DONE to 2.5: DONE, 2.6: DONE

ruby_2_5 r67774 merged revision(s) f91879a7b548284c93743168acfd11e3d2aeefac,9557069299ac3b96691040a541afa65761a724ad.

----------------------------------------
Bug #15992: An exception breaks monitor state and cause deadlock
https://bugs.ruby-lang.org/issues/15992#change-81046

* Author: naruse (Yui NARUSE)
* Status: Closed
* Priority: Normal
* Assignee: 
* Target version: 
* ruby -v: 
* Backport: 2.5: DONE, 2.6: DONE
----------------------------------------
lib/monitor.rb provides Monitor.
But its state handling is weak for interrupts caused by Thread.kill for example timeout libraries.

Timeout exception may happen everywhere. If it raised when the thread is executing

```ruby
  def mon_exit
    mon_check_owner
    @mon_count -=1
    if @mon_count == 0
      @mon_owner = nil
      # HERE!!!
      @mon_mutex.unlock
    end
  end
``` 

It breaks the state of the monitor and it causes deadlock.



-- 
https://bugs.ruby-lang.org/

[ruby-core:94591] [Ruby master Bug#15992] An exception breaks monitor state and cause deadlock

[eregontp]

Issue #15992 has been updated by Eregon (Benoit Daloze).


Should `mon_enter` and `mon_exit` use `Thread.handle_interrupt` inside their method definitions, so they are safe when called directly too?

`Thread.handle_interrupt(Exception => :never)` seems too much for `mon_enter`, I think `Thread.handle_interrupt(Exception => :blocking)` would be better.
Otherwise, it's not possible to interrupt a thread trying to get a contended monitor with `Thread#raise`:
```
ruby -rmonitor -e 'o=Object.new.extend(MonitorMixin); Thread.new{ o.mon_enter; sleep }; sleep 0.1; Thread.new{sleep 3; p :kill; Thread.main.raise "bye"}; p o.synchronize { p :in; sleep }'
```
Never exits on trunk, but it does exit on 2.6.2 and before. Even Thread#kill does not help.

Ctrl+C does interrupt it, because signal traps are not yet supported by `handle_interrupt`, but that might change.

----------------------------------------
Bug #15992: An exception breaks monitor state and cause deadlock
https://bugs.ruby-lang.org/issues/15992#change-81063

* Author: naruse (Yui NARUSE)
* Status: Closed
* Priority: Normal
* Assignee: 
* Target version: 
* ruby -v: 
* Backport: 2.5: DONE, 2.6: DONE
----------------------------------------
lib/monitor.rb provides Monitor.
But its state handling is weak for interrupts caused by Thread.kill for example timeout libraries.

Timeout exception may happen everywhere. If it raised when the thread is executing

```ruby
  def mon_exit
    mon_check_owner
    @mon_count -=1
    if @mon_count == 0
      @mon_owner = nil
      # HERE!!!
      @mon_mutex.unlock
    end
  end
``` 

It breaks the state of the monitor and it causes deadlock.



-- 
https://bugs.ruby-lang.org/