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42 lines
1.8 KiB
42 lines
1.8 KiB
4 months ago
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#######################################
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# C Globals and CPython Runtime State.
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CPython's C code makes extensive use of global variables. Each global
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falls into one of several categories:
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* (effectively) constants (incl. static types)
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* globals used exclusively in main or in the REPL
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* freelists, caches, and counters
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* process-global state
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* module state
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* Python runtime state
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The ignored-globals.txt file is organized similarly. Of the different
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categories, the last two are problematic and generally should not exist
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in the codebase.
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Globals that hold module state (i.e. in Modules/*.c) cause problems
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when multiple interpreters are in use. For more info, see PEP 3121,
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which addresses the situation for extension modules in general.
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Globals in the last category should be avoided as well. The problem
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isn't with the Python runtime having state. Rather, the problem is with
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that state being spread throughout the codebase in dozens of individual
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globals. Unlike the other globals, the runtime state represents a set
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of values that are constantly shifting in a complex way. When they are
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spread out it's harder to get a clear picture of what the runtime
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involves. Furthermore, when they are spread out it complicates efforts
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that change the runtime.
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Consequently, the globals for Python's runtime state have been
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consolidated under a single top-level _PyRuntime global. No new globals
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should be added for runtime state. Instead, they should be added to
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_PyRuntimeState or one of its sub-structs. The check-c-globals script
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should be run to ensure that no new globals have been added:
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python3 Tools/c-analyzer/check-c-globals.py
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If it reports any globals then they should be resolved. If the globals
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are runtime state then they should be folded into _PyRuntimeState.
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Otherwise they should be added to ignored-globals.txt.
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