1####################################### 2# C Globals and CPython Runtime State. 3 4CPython's C code makes extensive use of global variables. Each global 5falls into one of several categories: 6 7* (effectively) constants (incl. static types) 8* globals used exclusively in main or in the REPL 9* freelists, caches, and counters 10* process-global state 11* module state 12* Python runtime state 13 14The ignored-globals.txt file is organized similarly. Of the different 15categories, the last two are problematic and generally should not exist 16in the codebase. 17 18Globals that hold module state (i.e. in Modules/*.c) cause problems 19when multiple interpreters are in use. For more info, see PEP 3121, 20which addresses the situation for extension modules in general. 21 22Globals in the last category should be avoided as well. The problem 23isn't with the Python runtime having state. Rather, the problem is with 24that state being spread throughout the codebase in dozens of individual 25globals. Unlike the other globals, the runtime state represents a set 26of values that are constantly shifting in a complex way. When they are 27spread out it's harder to get a clear picture of what the runtime 28involves. Furthermore, when they are spread out it complicates efforts 29that change the runtime. 30 31Consequently, the globals for Python's runtime state have been 32consolidated under a single top-level _PyRuntime global. No new globals 33should be added for runtime state. Instead, they should be added to 34_PyRuntimeState or one of its sub-structs. The check-c-globals script 35should be run to ensure that no new globals have been added: 36 37 python3 Tools/c-globals/check-c-globals.py 38 39If it reports any globals then they should be resolved. If the globals 40are runtime state then they should be folded into _PyRuntimeState. 41Otherwise they should be added to ignored-globals.txt. 42