Make syncthreads() in parallel_xexec multi-use

[igchor]

Previously syncthreads could only be used once and this was not
documented. This patch allows for having multiple synchronization
points in a function. This might useful for testing hazard pointers.

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This change is 

[codecov]

Codecov Report

Merging #1062 (79ed022) into master (2bc7289) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1062   +/-   ##
=======================================
  Coverage   94.16%   94.16%           
=======================================
  Files          48       48           
  Lines        4751     4751           
=======================================
  Hits         4474     4474           
  Misses        277      277           

Flag	Coverage Δ
tests_clang_debug_cpp17	93.57% <ø> (-0.07%)	⬇️
tests_gcc_debug	92.09% <ø> (+0.11%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
include/libpmemobj++/condition_variable.hpp	76.19% <0.00%> (-2.39%)	⬇️
...ude/libpmemobj++/container/concurrent_hash_map.hpp	94.51% <0.00%> (+0.15%)	⬆️

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[lukaszstolarczuk]

Reviewed 3 of 3 files at r1.
Reviewable status: all files reviewed, 3 unresolved discussions (waiting on @igchor)

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tests/common/helpers_test.cpp, line 12 at r1 (raw file):

int
main()

pls add a short comment what's in this test

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tests/common/helpers_test.cpp, line 26 at r1 (raw file):

			       counter++;

you could add info that new latch is allocated here (if that's meaningful - I'm not sure... ;) )

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tests/common/helpers_test.cpp, line 31 at r1 (raw file):

			       syncthreads();
		       });
}

counter is still equal to concurrency * 2 at the end of main..? maybe we could assert that too

[igchor]

Reviewable status: all files reviewed, 3 unresolved discussions (waiting on @lukaszstolarczuk)

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tests/common/helpers_test.cpp, line 12 at r1 (raw file):

Previously, lukaszstolarczuk (Łukasz Stolarczuk) wrote…

pls add a short comment what's in this test

Done.

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tests/common/helpers_test.cpp, line 26 at r1 (raw file):

Previously, lukaszstolarczuk (Łukasz Stolarczuk) wrote…

you could add info that new latch is allocated here (if that's meaningful - I'm not sure... ;) )

I think that should not matter here - the fact that we allocate new latch is an implementation detail, this should just work :)

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tests/common/helpers_test.cpp, line 31 at r1 (raw file):

Previously, lukaszstolarczuk (Łukasz Stolarczuk) wrote…

counter is still equal to concurrency * 2 at the end of main..? maybe we could assert that too

Done.

[lukaszstolarczuk]

(just fix CI)

Reviewed 1 of 1 files at r2.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @igchor)

[igchor]

Done.

Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @igchor)

[KFilipek]

Reviewed 2 of 3 files at r1, 1 of 1 files at r3.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @igchor)

[lukaszstolarczuk]

Reviewed 1 of 1 files at r3, 2 of 2 files at r4.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @igchor)