Test fails on i386 and armhf architectures

[dleidert]

While running bundle exec rspec on an i386 architecture, this test fails:

Failures:

  1) RSpec::Memory on supported platform should not exceed specified size limit
     Failure/Error:
       expect do
       	"a" * 100_000
       end.to limit_allocations.of(String, size: 100_001)
     
       exceeded allocation limit: allocated 2 String instances, 99961 bytes, expected exactly 100001 bytes
     # ./spec/async/rspec/memory_spec.rb:82:in `block (3 levels) in <top (required)>'

Finished in 3.34 seconds (files took 0.25602 seconds to load)
19 examples, 1 failure

Failed examples:

rspec ./spec/async/rspec/memory_spec.rb:81 # RSpec::Memory on supported platform should not exceed specified size limit

The same happens on armhf machines.

[ioquatix]

Maybe the size of the string is being reported incorrectly.

[dleidert]

That might be a problem in rspec-memory. There is a similar test, and it is failing there too.

https://salsa.debian.org/ruby-team/ruby-rspec-memory/-/jobs/2231139#L1174

[dleidert]

@ioquatix , I found the problem. In rspec-memory the SLOT_SIZEvalue is defined as 40. However, for 32bit it is 20. I can verify this by comparing ("a"*100_000).size memsize_of("a"*100_000) on amd64 and i386 architectures, the first is 100041, the latter is 100021. If I change the value on i386 to 20 and run the tests of rspec-memory again, it works.

I found only some very old documentation and I have no idea how to determine the size correctly based on the architecture instead of setting it statically.

[dleidert]

What about this approach in rspec-memory:

diff --git a/lib/rspec/memory/trace.rb b/lib/rspec/memory/trace.rb
index 1778338..2d4d5ce 100644
--- a/lib/rspec/memory/trace.rb
+++ b/lib/rspec/memory/trace.rb
@@ -23,13 +23,11 @@ require 'objspace'
 module RSpec
        module Memory
                Allocation = Struct.new(:count, :size) do
-                       SLOT_SIZE = 40
-                       
                        def << object
                                self.count += 1
                                
                                # We don't want to force specs to take the slot size into account.
-                               self.size += ObjectSpace.memsize_of(object) - SLOT_SIZE
+                               self.size += ObjectSpace.memsize_of(object) - ObjectSpace.memsize_of(object.class.new)
                        end
                        
                        def self.default_hash

[ioquatix]

This should be fixed according to the linked PRs.