Remove scheduling dependency from XRay :: Posix/fork_basic_logging.cc

[ormris]

Summary

We've been seeing intermittent failures on our internal bots and we suspect
this may be due to the OS scheduling the child process to run before the parent
process.

This version ensures that the parent and child can be run in either order.

[dberris]

LGTM

I've been wondering the same with local failures but hadn't looked at it closely, thanks @ormris!

The scheduling dependency definitely is not required in this test.

[ormris]

Thanks for the review! Before I commit this, would it be possible to change the second part of the test (after line 82) to be scheduling independent?

[dberris]

In D49501#1167385, @ormris wrote:

Thanks for the review! Before I commit this, would it be possible to change the second part of the test (after line 82) to be scheduling independent?

The secondary test already should do that, since it's already looking for independent process markers. If it's not doing the right thing, then we (@Maknee or I) should look into how to re-structure this test to be less dependent on scheduling (maybe looking for a different function called from the child and the parent).

[ormris]

OK. I'll commit this and see if it fixes the issues.

[Maknee]

Sorry for responding so late -- I noticed that this was happening too.

Thanks for finding and fixing the issue.

[ormris]

@Maknee We're now seeing intermittent failures for the second part of the test (after line 83). Is that part of the test scheduling independent? I see that the comments say "// The parent will print its pid first".

[Maknee]

There is an ordering currently (There shouldn't have been)

On lines 92 and 100, TRACE should be TRACE-DAG.

Refer to https://reviews.llvm.org/D49559

test/xray/TestCases/Posix/fork_basic_logging.cc

 }
 
 int main()
 {
   parent_tid = log_syscall_gettid();
   if(fork())
   {
     print_parent_or_child();
-      // CHECK: Parent with tid
+      // CHECK-DAG: Parent with tid
   }
   else
   {
     print_parent_or_child();
-      // CHECK: Child with tid
+      // CHECK-DAG: Child with tid
   }
   return 0;
 }
 
 // Make sure we know which thread is the parent process
 // TRACE-DAG: - { type: 0, func-id: [[LSGT:[0-9]+]], function: {{.*log_syscall_gettid.*}}, cpu: {{.*}}, thread: [[THREAD1:[0-9]+]], process: [[PROCESS1:[0-9]+]], kind: function-enter, tsc: {{[0-9]+}} }
 
 // TRACE-DAG: - { type: 0, func-id: [[PPOC:[0-9]+]], function: {{.*print_parent_or_child.*}}, cpu: {{.*}}, thread: [[THREAD1]], process: [[PROCESS1]], kind: function-enter, tsc: {{[0-9]+}} }