/* N pthreads, each: PyGILState_Ensure -> loop of 5,000x PyEval_SaveThread/RestoreThread -> PyGILState_Release.
   Trigger: >=8 threads (deterministic at 8, 12, 16, 20 on every version tested);
   6 and below: passes. 

cc -O2 -pthread -o repro repro_ft.c \
   -I/tmp/<prefix>/include/python3.1Xt \
   /tmp/<prefix>/lib/libpython3.1Xt.a -lpthread -lm -lutil -ldl

timeout 45 ./repro 8   # -> "launched worker 8" then HANG (exit 124)
*/
#include <Python.h>
#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>

static volatile long long counter = 0;
static volatile int g_stop = 0;
static int g_iters = 5000;
static int g_mode = 1;  /* 1=churn, 0=once */

static void *worker(void *arg) {
    PyGILState_STATE st = PyGILState_Ensure();
    long long n = 0;
    for (long long i = 0; i < g_iters && !g_stop; i++) {
        if (g_mode == 0) { /* once: already ensured once, loop is Save/Restore only */
        }
        PyThreadState *ts = PyEval_SaveThread();
        for (volatile int k = 0; k < 100; k++) {}
        PyEval_RestoreThread(ts);
        n++;
    }
    PyGILState_Release(st);
    __sync_fetch_and_add(&counter, n);
    return NULL;
}

int main(int argc, char **argv) {
    int n = argc > 1 ? atoi(argv[1]) : 8;
    g_mode = argc > 2 && !strcmp(argv[2], "once") ? 0 : 1;
    g_iters = argc > 3 ? (int)atol(argv[3]) : 5000;
    Py_Initialize();
    fprintf(stderr, "Py_VERSION=%s\n", Py_GetVersion());
    pthread_t *t = malloc(sizeof(pthread_t) * n);
    for (int i = 0; i < n; i++) { pthread_create(&t[i], NULL, worker, NULL); fprintf(stderr, "launched worker %d\n", i); }
    for (int i = 0; i < n; i++) pthread_join(t[i], NULL);
    fprintf(stderr, "ALL WORKERS COMPLETED (PASS) counter=%lld\n", counter);
    Py_Finalize();
    return 0;
}