Trap earlier when a Thread instance is re-used #3862

c1728p9 · 2017-03-01T20:39:53Z

Calling Thread::start multiple times leads to undefined behavior since the Thread class was not designed to handle this. Add an assert to trap immediately if Thread::start is called a second time to prevent this behavior.

c1728p9 · 2017-03-01T20:40:02Z

/morph test

geky · 2017-03-01T21:48:31Z

rtos/Thread.h

@@ -347,6 +347,7 @@ class Thread {
    bool _dynamic_stack;
    Semaphore _join_sem;
    Mutex _mutex;
+    bool _finished;


Random thought: Should we be ifdeffing these variables out or something for non-debug builds? Otherwise they are just wasting space.

Na, its just one byte.

I needed to update the PR anyway so I re-ordered this so the size stays the same 😲.

geky

This looks reasonable if we only want a thread to be startable once 👍

mbed-bot · 2017-03-01T22:19:55Z

Result: FAILURE

Your command has finished executing! Here's what you wrote!

/morph test

Output

mbed Build Number: 1611

Test failed!

c1728p9 · 2017-03-01T22:49:21Z

/morph test

mbed-bot · 2017-03-01T23:58:25Z

Result: FAILURE

Your command has finished executing! Here's what you wrote!

/morph test

Output

mbed Build Number: 1612

Test failed!

0xc0170 · 2017-03-02T10:36:18Z

/morph test

pan-

Could you update the documentation to reflect these changes and precise that it is not allowed to start a terminated thread ?

It is not indicated in the documentation and without this precision it is easy to guess that it is possible to reuse a terminated thread.

The API is also inconsistent because there is no way to differentiate a thread not started from a thread terminated.

rtos::Thread t; 
assert(t.get_state() == Thread::Deleted); 

t.start(...)
assert(t.get_state() != Thread::Deleted); 

t.join(); // || t.terminate()
assert(t.get_state() == Thread::Deleted);

As a result it is impossible to start a Thread safely outside from its declaration site:

bool exec_on_thread(Thread& t) { 
    // might trap ... no way to avoid it by testing the state
    t.start(....);
}

Last point, is it necessary to trap. Thread::start was introduced to catch failure at user level and now an assertion for a non testable condition is introduced, I'm not sure to understand the logic.

bridadan · 2017-03-02T15:10:16Z

I believe for the second run one ARCH_PRO and one HEXIWEAR had been knocked offline as the issue persisted in other CI runs. I have reset them so hopefully the same problem won't affect this run.

mbed-bot · 2017-03-02T15:42:12Z

Result: SUCCESS

Your command has finished executing! Here's what you wrote!

/morph test

Output

mbed Build Number: 1616

All builds and test passed!

tim-nordell-nimbelink · 2017-03-02T19:39:37Z

I agree with @pan- that the documentation for the class should be updated to reflect this. It should be mentioned within the start() function documentation (that it cannot be restarted even if the thread has been terminated), and possibly in the overview of the class above the definition of the class as well.

c1728p9 · 2017-03-03T17:36:27Z

Since start returns an error code currently I updated this PR return an error rather than asserting. I also added a way to distinguish a thread that hasn't been started from a thread that has terminated.

c1728p9 · 2017-03-03T17:36:36Z

/morph test

mbed-bot · 2017-03-03T19:21:14Z

Result: FAILURE

Your command has finished executing! Here's what you wrote!

/morph test

Output

mbed Build Number: 1622

Test failed!

0xc0170 · 2017-03-06T13:32:57Z

@pan- Please review again

pan- · 2017-03-06T13:47:33Z

@0xc0170 Thanks to @c1728p9 the API is now consistent but the behavior (threads can be only started once) is still not documented.

I also wonder if it wouldn't be a good thing to enforce that instances have well defined and unique identity by forbidding copy constructor and copy assignment operator.

c1728p9 · 2017-03-06T17:09:38Z

@pan- the thread being started only once is documented here

pan- · 2017-03-06T17:12:25Z

@c1728p9 My bad, I missed that line 😞 .
LGTM

c1728p9 · 2017-03-06T17:24:23Z

/morph test

tim-nordell-nimbelink · 2017-03-06T17:29:09Z

rtos/Thread.h

@@ -197,6 +197,7 @@ class Thread {
    /** Starts a thread executing the specified function.
      @param   task           function to be executed by this thread.
      @return  status code that indicates the execution status of the function.
+      @note a thread can only be stared once


Should be "started once" and not "stared once".

Thanks for catching this @tim-nordell-nimbelink

Calling Thread::start multiple times leads to undefined behavior since the Thread class was not designed to handle being restarted. Return an error code if Thread::start is called a second time to prevent this behavior.

If a thread hasn't been started return Inactive as the status when Thread::get_state() is called.

Make the copy constructor and assignment operator private to prevent them from being used.

c1728p9 · 2017-03-06T17:56:38Z

/morph test

c1728p9 · 2017-03-06T17:57:47Z

@pan- I make the copy constructor and assignment operator private.

mbed-bot · 2017-03-06T21:24:01Z

Result: FAILURE

Your command has finished executing! Here's what you wrote!

/morph test

mbed-bot · 2017-03-06T22:29:18Z

Result: SUCCESS

Your command has finished executing! Here's what you wrote!

/morph test

Output

mbed Build Number: 1646

All builds and test passed!

c1728p9 mentioned this pull request Mar 1, 2017

Two iterations of Thread start(), join() causes mbed_die() #3774

Closed

c1728p9 requested review from geky and 0xc0170 March 1, 2017 20:40

geky reviewed Mar 1, 2017

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geky approved these changes Mar 1, 2017

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c1728p9 force-pushed the thread_start_assert branch from 507ac38 to 5d3ce1a Compare March 1, 2017 22:49

0xc0170 approved these changes Mar 2, 2017

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0xc0170 added the needs: CI label Mar 2, 2017

pan- requested changes Mar 2, 2017

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c1728p9 force-pushed the thread_start_assert branch from ea46471 to f985a47 Compare March 3, 2017 17:33

0xc0170 added needs: work and removed needs: CI labels Mar 6, 2017

tim-nordell-nimbelink reviewed Mar 6, 2017

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rtos: Return an error when a Thread is re-used

11ef1d1

Calling Thread::start multiple times leads to undefined behavior since the Thread class was not designed to handle being restarted. Return an error code if Thread::start is called a second time to prevent this behavior.

c1728p9 added 2 commits March 6, 2017 11:54

rtos: Add Inactive return to thread get state

05403d4

If a thread hasn't been started return Inactive as the status when Thread::get_state() is called.

rtos: Prevent Thread class from being copied

ab4da40

Make the copy constructor and assignment operator private to prevent them from being used.

c1728p9 force-pushed the thread_start_assert branch from f985a47 to ab4da40 Compare March 6, 2017 17:56

0xc0170 added ready for merge needs: CI and removed needs: work ready for merge needs: CI labels Mar 7, 2017

adbridge added release-version: 5.4.2 and removed ready for merge labels Mar 14, 2017

adbridge merged commit 88fb819 into ARMmbed:master Mar 14, 2017

adustm mentioned this pull request Apr 11, 2017

fix #3863 Add an mbed API that allows the init of the CAN at the bus frequency #4165

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Trap earlier when a Thread instance is re-used #3862

Trap earlier when a Thread instance is re-used #3862

c1728p9 commented Mar 1, 2017

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0xc0170 commented Mar 6, 2017

pan- commented Mar 6, 2017

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mbed-bot commented Mar 6, 2017

Trap earlier when a Thread instance is re-used #3862

Trap earlier when a Thread instance is re-used #3862

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