pystate.h

#ifndef Py_CPYTHON_PYSTATE_H
#  error "this header file must not be included directly"
#endif


/* private interpreter helpers */

PyAPI_FUNC(int) _PyInterpreterState_RequiresIDRef(PyInterpreterState *);
PyAPI_FUNC(void) _PyInterpreterState_RequireIDRef(PyInterpreterState *, int);

PyAPI_FUNC(PyObject *) PyUnstable_InterpreterState_GetMainModule(PyInterpreterState *);

/* State unique per thread */

/* Py_tracefunc return -1 when raising an exception, or 0 for success. */
typedef int (*Py_tracefunc)(PyObject *, PyFrameObject *, int, PyObject *);

/* The following values are used for 'what' for tracefunc functions
 *
 * To add a new kind of trace event, also update "trace_init" in
 * Python/sysmodule.c to define the Python level event name
 */
#define PyTrace_CALL 0
#define PyTrace_EXCEPTION 1
#define PyTrace_LINE 2
#define PyTrace_RETURN 3
#define PyTrace_C_CALL 4
#define PyTrace_C_EXCEPTION 5
#define PyTrace_C_RETURN 6
#define PyTrace_OPCODE 7

typedef struct _err_stackitem {
    /* This struct represents a single execution context where we might
     * be currently handling an exception.  It is a per-coroutine state
     * (coroutine in the computer science sense, including the thread
     * and generators).
     *
     * This is used as an entry on the exception stack, where each
     * entry indicates if it is currently handling an exception.
     * This ensures that the exception state is not impacted
     * by "yields" from an except handler.  The thread
     * always has an entry (the bottom-most one).
     */

    /* The exception currently being handled in this context, if any. */
    PyObject *exc_value;

    struct _err_stackitem *previous_item;

} _PyErr_StackItem;

typedef struct _stack_chunk {
    struct _stack_chunk *previous;
    size_t size;
    size_t top;
    PyObject * data[1]; /* Variable sized */
} _PyStackChunk;

struct _py_trashcan {
    int delete_nesting;
    PyObject *delete_later;
};

struct _ts {
    /* See Python/ceval.c for comments explaining most fields */

    PyThreadState *prev;
    PyThreadState *next;
    PyInterpreterState *interp;

    struct {
        /* Has been initialized to a safe state.

           In order to be effective, this must be set to 0 during or right
           after allocation. */
        unsigned int initialized:1;

        /* Has been bound to an OS thread. */
        unsigned int bound:1;
        /* Has been unbound from its OS thread. */
        unsigned int unbound:1;
        /* Has been bound aa current for the GILState API. */
        unsigned int bound_gilstate:1;
        /* Currently in use (maybe holds the GIL). */
        unsigned int active:1;

        /* various stages of finalization */
        unsigned int finalizing:1;
        unsigned int cleared:1;
        unsigned int finalized:1;

        /* padding to align to 4 bytes */
        unsigned int :24;
    } _status;
#ifdef Py_BUILD_CORE
#  define _PyThreadState_WHENCE_NOTSET -1
#  define _PyThreadState_WHENCE_UNKNOWN 0
#  define _PyThreadState_WHENCE_INTERP 1
#  define _PyThreadState_WHENCE_THREADING 2
#  define _PyThreadState_WHENCE_GILSTATE 3
#  define _PyThreadState_WHENCE_EXEC 4
#endif
    int _whence;

    /* Thread state (_Py_THREAD_ATTACHED, _Py_THREAD_DETACHED, _Py_THREAD_GC).
       See Include/internal/pycore_pystate.h for more details. */
    int state;

    int py_recursion_remaining;
    int py_recursion_limit;

    int c_recursion_remaining;
    int recursion_headroom; /* Allow 50 more calls to handle any errors. */

    /* 'tracing' keeps track of the execution depth when tracing/profiling.
       This is to prevent the actual trace/profile code from being recorded in
       the trace/profile. */
    int tracing;
    int what_event; /* The event currently being monitored, if any. */

    /* Pointer to currently executing frame. */
    struct _PyInterpreterFrame *current_frame;

    Py_tracefunc c_profilefunc;
    Py_tracefunc c_tracefunc;
    PyObject *c_profileobj;
    PyObject *c_traceobj;

    /* The exception currently being raised */
    PyObject *current_exception;

    /* Pointer to the top of the exception stack for the exceptions
     * we may be currently handling.  (See _PyErr_StackItem above.)
     * This is never NULL. */
    _PyErr_StackItem *exc_info;

    PyObject *dict;  /* Stores per-thread state */

    int gilstate_counter;

    PyObject *async_exc; /* Asynchronous exception to raise */
    unsigned long thread_id; /* Thread id where this tstate was created */

    /* Native thread id where this tstate was created. This will be 0 except on
     * those platforms that have the notion of native thread id, for which the
     * macro PY_HAVE_THREAD_NATIVE_ID is then defined.
     */
    unsigned long native_thread_id;

    struct _py_trashcan trash;

    /* Tagged pointer to top-most critical section, or zero if there is no
     * active critical section. Critical sections are only used in
     * `--disable-gil` builds (i.e., when Py_GIL_DISABLED is defined to 1). In the
     * default build, this field is always zero.
     */
    uintptr_t critical_section;

    /* Called when a thread state is deleted normally, but not when it
     * is destroyed after fork().
     * Pain:  to prevent rare but fatal shutdown errors (issue 18808),
     * Thread.join() must wait for the join'ed thread's tstate to be unlinked
     * from the tstate chain.  That happens at the end of a thread's life,
     * in pystate.c.
     * The obvious way doesn't quite work:  create a lock which the tstate
     * unlinking code releases, and have Thread.join() wait to acquire that
     * lock.  The problem is that we _are_ at the end of the thread's life:
     * if the thread holds the last reference to the lock, decref'ing the
     * lock will delete the lock, and that may trigger arbitrary Python code
     * if there's a weakref, with a callback, to the lock.  But by this time
     * _PyRuntime.gilstate.tstate_current is already NULL, so only the simplest
     * of C code can be allowed to run (in particular it must not be possible to
     * release the GIL).
     * So instead of holding the lock directly, the tstate holds a weakref to
     * the lock:  that's the value of on_delete_data below.  Decref'ing a
     * weakref is harmless.
     * on_delete points to _threadmodule.c's static release_sentinel() function.
     * After the tstate is unlinked, release_sentinel is called with the
     * weakref-to-lock (on_delete_data) argument, and release_sentinel releases
     * the indirectly held lock.
     */
    void (*on_delete)(void *);
    void *on_delete_data;

    int coroutine_origin_tracking_depth;

    PyObject *async_gen_firstiter;
    PyObject *async_gen_finalizer;

    PyObject *context;
    uint64_t context_ver;

    /* Unique thread state id. */
    uint64_t id;

    _PyStackChunk *datastack_chunk;
    PyObject **datastack_top;
    PyObject **datastack_limit;
    /* XXX signal handlers should also be here */

    /* The following fields are here to avoid allocation during init.
       The data is exposed through PyThreadState pointer fields.
       These fields should not be accessed directly outside of init.
       This is indicated by an underscore prefix on the field names.

       All other PyInterpreterState pointer fields are populated when
       needed and default to NULL.
       */
       // Note some fields do not have a leading underscore for backward
       // compatibility.  See https://bugs.python.org/issue45953#msg412046.

    /* The thread's exception stack entry.  (Always the last entry.) */
    _PyErr_StackItem exc_state;

};

#ifdef Py_DEBUG
   // A debug build is likely built with low optimization level which implies
   // higher stack memory usage than a release build: use a lower limit.
#  define Py_C_RECURSION_LIMIT 500
#elif defined(__wasi__)
   // WASI has limited call stack. Python's recursion limit depends on code
   // layout, optimization, and WASI runtime. Wasmtime can handle about 700
   // recursions, sometimes less. 500 is a more conservative limit.
#  define Py_C_RECURSION_LIMIT 500
#else
   // This value is duplicated in Lib/test/support/__init__.py
#  define Py_C_RECURSION_LIMIT 1500
#endif


/* other API */

/* Similar to PyThreadState_Get(), but don't issue a fatal error
 * if it is NULL. */
PyAPI_FUNC(PyThreadState *) PyThreadState_GetUnchecked(void);

// Alias kept for backward compatibility
#define _PyThreadState_UncheckedGet PyThreadState_GetUnchecked


// Disable tracing and profiling.
PyAPI_FUNC(void) PyThreadState_EnterTracing(PyThreadState *tstate);

// Reset tracing and profiling: enable them if a trace function or a profile
// function is set, otherwise disable them.
PyAPI_FUNC(void) PyThreadState_LeaveTracing(PyThreadState *tstate);

/* PyGILState */

/* Helper/diagnostic function - return 1 if the current thread
   currently holds the GIL, 0 otherwise.

   The function returns 1 if _PyGILState_check_enabled is non-zero. */
PyAPI_FUNC(int) PyGILState_Check(void);

/* The implementation of sys._current_frames()  Returns a dict mapping
   thread id to that thread's current frame.
*/
PyAPI_FUNC(PyObject*) _PyThread_CurrentFrames(void);

/* Routines for advanced debuggers, requested by David Beazley.
   Don't use unless you know what you are doing! */
PyAPI_FUNC(PyInterpreterState *) PyInterpreterState_Main(void);
PyAPI_FUNC(PyInterpreterState *) PyInterpreterState_Head(void);
PyAPI_FUNC(PyInterpreterState *) PyInterpreterState_Next(PyInterpreterState *);
PyAPI_FUNC(PyThreadState *) PyInterpreterState_ThreadHead(PyInterpreterState *);
PyAPI_FUNC(PyThreadState *) PyThreadState_Next(PyThreadState *);
PyAPI_FUNC(void) PyThreadState_DeleteCurrent(void);

/* Frame evaluation API */

typedef PyObject* (*_PyFrameEvalFunction)(PyThreadState *tstate, struct _PyInterpreterFrame *, int);

PyAPI_FUNC(_PyFrameEvalFunction) _PyInterpreterState_GetEvalFrameFunc(
    PyInterpreterState *interp);
PyAPI_FUNC(void) _PyInterpreterState_SetEvalFrameFunc(
    PyInterpreterState *interp,
    _PyFrameEvalFunction eval_frame);