Implement task kill

[wangrunji0408]

Implement syscall:

• zx_task_kill

[xy-plus]

接单

[xy-plus]

放弃

[benpigchu]

Let me take this.

[benpigchu]

@xy-plus has an implementation in the task_kill branch.

The implementation in that branch do not pass the Threads.KillSuspendedThread case [test case code]

This test case use debug exception channel (!) to check if the thread is exiting. so it won't pass until the debug exception channel is implemented. See #68

[benpigchu]

However, we should reset suspend_count to zero before waking waker, so that the RunnableChecker won't set waker again.

[benpigchu]

The code won't compile if we merge changes from #87, we should still use process_exit to remove the process from the job.

[benpigchu]

Now my fork were successfully merged into current master.
There are still two thing to implemented:

• killing a blocked thread
• killing the job.

[benpigchu]

To kill a blocked thread:

In zcore, we use blocking_run to block the thread. It do the following things:

1. lock the thread lock and replace the state
2. run the future
3. lock the thread lock again and recover the state

So, to kill a blocking thread, we need to check if the thread is dying in 1, stop the future running in 2 (with a cancel token?), and check if the thread is dying again in 3.

If the thread was killed in blocking_run , I think we should make it returns a special error code (like ZxError::STOP) to indicate the thread is killed.

As a test, Thread.SuspendAfterDeath should pass after this.

[wangrunji0408]

Also need to add another cancel token to wakeup the blocking thread?

[benpigchu]

Job killing is actually implemented by @xy-plus , so I simply add it to the syscall body. However, we should set the signal and forbid following child job and process creating.

[benpigchu]

Seems there is a deadlock in the task kill implementation found on the CI

When killing the job, the child process is killed, then the child process remove itself from the parent job. which forms a deadlock.