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copy.copy and copy.deepcopy scale poorly with free-threading #132657

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@eendebakpt

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@eendebakpt

The copy.copy and copy.deepcopy operations running on different objects in different threads should be able to run independently. The scaling is not good: output of the ftscalingbench.py with added benchmarks:

Running benchmarks with 8 threads
shallow_copy               4.6x slower
deepcopy                   2.3x slower
object_cfunction           5.9x faster
cmodule_function           5.9x faster
object_lookup_special      5.5x faster
mult_constant              5.6x faster
generator                  4.9x faster
pymethod                   5.2x faster
pyfunction                 4.5x faster
module_function            5.0x faster
load_string_const          5.6x faster
load_tuple_const           5.9x faster
create_pyobject            2.3x faster
create_closure             7.1x faster
create_dict                3.3x faster
thread_local_read          3.3x faster

There are at least two reasons:

  • The copy module uses module level variables in the copy.copy and copy.deepcopy methods.
  • The _copy_atomic_types (and some similar data structures) is a set which requires locking for membership testing.

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    performancePerformance or resource usagestdlibPython modules in the Lib dirtopic-free-threadingtype-bugAn unexpected behavior, bug, or error

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