helgrind.md

Helgrind outputs

Simple data race

We clearly see were are the conflicting load and store as well as where the concerned threads have been created. And all that in a digest manner.

String data race

It is a little bit more messy with strings (4 errors), but we have the information.

You also have the concerned symbol "_Z1xB5cxx11". I don't know why helgrind does not demangle it. But you could do it with c++filt. And here we have our variable name: x[abi:cxx11]

...

Pseudo notification

Helgrind shows us the 3 data races, with duplicate, but it is clear.

Data race with notification flag:

Data race with first part of the string:

Data race with second part of the string:

std::map data race

With a lot of errors Helgrind points the race, we can watch only the first error:

Data race vs race condition

With the little help of grep we see all the data race:

grep -E "(data_race|conflicts|data race)"

Data race on object destruction

This is not really the job of helgrind to detect this, memcheck or other memory check can detect this error.

Data race on small string destruction

Again as said above this is note the job of helgrind.

Data race on string destruction

Again as said above this is note the job of helgrind.

ABA

Helgrind does not detect the ABA problem exposed in this code.
Even after looping 1000 times multiple times.

ABA synchronized

Even with synchronization Helgrind does not detect the problem on Gcc.
However with clang + libc++ Helgrind does detect a problem:

Notification load relaxed

Helgrind detect a data race on payload this is good.
However if we put annotations this hide the error. We must take care of using them correctly.
Also atomic access must be suppressed.

Notification load relaxed in loop

Same as before helgrind can detect the error if we use annotations correctly.

Notification load/store relaxed

Same as before helgrind can detect the error if we use annotations correctly.

Data race atomic fix

Helgrind on gcc report error on atomics and again we can suppress these, clang does not.

Data race atomic fix relaxed

Helgrind on gcc report error on atomics and again we can suppress these, clang this time also report errors.

Notification fix

As it was said before we must annotate the code to make helgrind understand the happens-before relations.

ABA fix

Helgrind does not detect anything.