Edit File: _embedding.h
/***** Support code for embedding *****/ #ifdef __cplusplus extern "C" { #endif #if defined(_WIN32) # define CFFI_DLLEXPORT __declspec(dllexport) #elif defined(__GNUC__) # define CFFI_DLLEXPORT __attribute__((visibility("default"))) #else # define CFFI_DLLEXPORT /* nothing */ #endif /* There are two global variables of type _cffi_call_python_fnptr: * _cffi_call_python, which we declare just below, is the one called by ``extern "Python"`` implementations. * _cffi_call_python_org, which on CPython is actually part of the _cffi_exports[] array, is the function pointer copied from _cffi_backend. After initialization is complete, both are equal. However, the first one remains equal to &_cffi_start_and_call_python until the very end of initialization, when we are (or should be) sure that concurrent threads also see a completely initialized world, and only then is it changed. */ #undef _cffi_call_python typedef void (*_cffi_call_python_fnptr)(struct _cffi_externpy_s *, char *); static void _cffi_start_and_call_python(struct _cffi_externpy_s *, char *); static _cffi_call_python_fnptr _cffi_call_python = &_cffi_start_and_call_python; #ifndef _MSC_VER /* --- Assuming a GCC not infinitely old --- */ # define cffi_compare_and_swap(l,o,n) __sync_bool_compare_and_swap(l,o,n) # define cffi_write_barrier() __sync_synchronize() # if !defined(__amd64__) && !defined(__x86_64__) && \ !defined(__i386__) && !defined(__i386) # define cffi_read_barrier() __sync_synchronize() # else # define cffi_read_barrier() (void)0 # endif #else /* --- Windows threads version --- */ # include <Windows.h> # define cffi_compare_and_swap(l,o,n) \ (InterlockedCompareExchangePointer(l,n,o) == (o)) # define cffi_write_barrier() InterlockedCompareExchange(&_cffi_dummy,0,0) # define cffi_read_barrier() (void)0 static volatile LONG _cffi_dummy; #endif #ifdef WITH_THREAD # ifndef _MSC_VER # include <pthread.h> static pthread_mutex_t _cffi_embed_startup_lock; # else static CRITICAL_SECTION _cffi_embed_startup_lock; # endif static char _cffi_embed_startup_lock_ready = 0; #endif static void _cffi_acquire_reentrant_mutex(void) { static void *volatile lock = NULL; while (!cffi_compare_and_swap(&lock, NULL, (void *)1)) { /* should ideally do a spin loop instruction here, but hard to do it portably and doesn't really matter I think: pthread_mutex_init() should be very fast, and this is only run at start-up anyway. */ } #ifdef WITH_THREAD if (!_cffi_embed_startup_lock_ready) { # ifndef _MSC_VER pthread_mutexattr_t attr; pthread_mutexattr_init(&attr); pthread_mutexattr_settype(&attr, PTHREAD_MUTEX_RECURSIVE); pthread_mutex_init(&_cffi_embed_startup_lock, &attr); # else InitializeCriticalSection(&_cffi_embed_startup_lock); # endif _cffi_embed_startup_lock_ready = 1; } #endif while (!cffi_compare_and_swap(&lock, (void *)1, NULL)) ; #ifndef _MSC_VER pthread_mutex_lock(&_cffi_embed_startup_lock); #else EnterCriticalSection(&_cffi_embed_startup_lock); #endif } static void _cffi_release_reentrant_mutex(void) { #ifndef _MSC_VER pthread_mutex_unlock(&_cffi_embed_startup_lock); #else LeaveCriticalSection(&_cffi_embed_startup_lock); #endif } /********** CPython-specific section **********/ #ifndef PYPY_VERSION #include "_cffi_errors.h" #define _cffi_call_python_org _cffi_exports[_CFFI_CPIDX] PyMODINIT_FUNC _CFFI_PYTHON_STARTUP_FUNC(void); /* forward */ static void _cffi_py_initialize(void) { /* XXX use initsigs=0, which "skips initialization registration of signal handlers, which might be useful when Python is embedded" according to the Python docs. But review and think if it should be a user-controllable setting. XXX we should also give a way to write errors to a buffer instead of to stderr. XXX if importing 'site' fails, CPython (any version) calls exit(). Should we try to work around this behavior here? */ Py_InitializeEx(0); } static int _cffi_initialize_python(void) { /* This initializes Python, imports _cffi_backend, and then the present .dll/.so is set up as a CPython C extension module. */ int result; PyGILState_STATE state; PyObject *pycode=NULL, *global_dict=NULL, *x; state = PyGILState_Ensure(); /* Call the initxxx() function from the present module. It will create and initialize us as a CPython extension module, instead of letting the startup Python code do it---it might reimport the same .dll/.so and get maybe confused on some platforms. It might also have troubles locating the .dll/.so again for all I know. */ (void)_CFFI_PYTHON_STARTUP_FUNC(); if (PyErr_Occurred()) goto error; /* Now run the Python code provided to ffi.embedding_init_code(). */ pycode = Py_CompileString(_CFFI_PYTHON_STARTUP_CODE, "<init code for '" _CFFI_MODULE_NAME "'>", Py_file_input); if (pycode == NULL) goto error; global_dict = PyDict_New(); if (global_dict == NULL) goto error; if (PyDict_SetItemString(global_dict, "__builtins__", PyThreadState_GET()->interp->builtins) < 0) goto error; x = PyEval_EvalCode( #if PY_MAJOR_VERSION < 3 (PyCodeObject *) #endif pycode, global_dict, global_dict); if (x == NULL) goto error; Py_DECREF(x); /* Done! Now if we've been called from _cffi_start_and_call_python() in an ``extern "Python"``, we can only hope that the Python code did correctly set up the corresponding @ffi.def_extern() function. Otherwise, the general logic of ``extern "Python"`` functions (inside the _cffi_backend module) will find that the reference is still missing and print an error. */ result = 0; done: Py_XDECREF(pycode); Py_XDECREF(global_dict); PyGILState_Release(state); return result; error:; { /* Print as much information as potentially useful. Debugging load-time failures with embedding is not fun */ PyObject *ecap; PyObject *exception, *v, *tb, *f, *modules, *mod; PyErr_Fetch(&exception, &v, &tb); ecap = _cffi_start_error_capture(); f = PySys_GetObject((char *)"stderr"); if (f != NULL && f != Py_None) { PyFile_WriteString( "Failed to initialize the Python-CFFI embedding logic:\n\n", f); } if (exception != NULL) { PyErr_NormalizeException(&exception, &v, &tb); PyErr_Display(exception, v, tb); } Py_XDECREF(exception); Py_XDECREF(v); Py_XDECREF(tb); if (f != NULL && f != Py_None) { PyFile_WriteString("\nFrom: " _CFFI_MODULE_NAME "\ncompiled with cffi version: 1.11.5" "\n_cffi_backend module: ", f); modules = PyImport_GetModuleDict(); mod = PyDict_GetItemString(modules, "_cffi_backend"); if (mod == NULL) { PyFile_WriteString("not loaded", f); } else { v = PyObject_GetAttrString(mod, "__file__"); PyFile_WriteObject(v, f, 0); Py_XDECREF(v); } PyFile_WriteString("\nsys.path: ", f); PyFile_WriteObject(PySys_GetObject((char *)"path"), f, 0); PyFile_WriteString("\n\n", f); } _cffi_stop_error_capture(ecap); } result = -1; goto done; } PyAPI_DATA(char *) _PyParser_TokenNames[]; /* from CPython */ static int _cffi_carefully_make_gil(void) { /* This does the basic initialization of Python. It can be called completely concurrently from unrelated threads. It assumes that we don't hold the GIL before (if it exists), and we don't hold it afterwards. (What it really does used to be completely different in Python 2 and Python 3, with the Python 2 solution avoiding the spin-lock around the Py_InitializeEx() call. However, after recent changes to CPython 2.7 (issue #358) it no longer works. So we use the Python 3 solution everywhere.) This initializes Python by calling Py_InitializeEx(). Important: this must not be called concurrently at all. So we use a global variable as a simple spin lock. This global variable must be from 'libpythonX.Y.so', not from this cffi-based extension module, because it must be shared from different cffi-based extension modules. We choose _PyParser_TokenNames[0] as a completely arbitrary pointer value that is never written to. The default is to point to the string "ENDMARKER". We change it temporarily to point to the next character in that string. (Yes, I know it's REALLY obscure.) */ #ifdef WITH_THREAD char *volatile *lock = (char *volatile *)_PyParser_TokenNames; char *old_value; while (1) { /* spin loop */ old_value = *lock; if (old_value[0] == 'E') { assert(old_value[1] == 'N'); if (cffi_compare_and_swap(lock, old_value, old_value + 1)) break; } else { assert(old_value[0] == 'N'); /* should ideally do a spin loop instruction here, but hard to do it portably and doesn't really matter I think: PyEval_InitThreads() should be very fast, and this is only run at start-up anyway. */ } } #endif /* call Py_InitializeEx() */ { PyGILState_STATE state = PyGILState_UNLOCKED; if (!Py_IsInitialized()) _cffi_py_initialize(); else state = PyGILState_Ensure(); PyEval_InitThreads(); PyGILState_Release(state); } #ifdef WITH_THREAD /* release the lock */ while (!cffi_compare_and_swap(lock, old_value + 1, old_value)) ; #endif return 0; } /********** end CPython-specific section **********/ #else /********** PyPy-specific section **********/ PyMODINIT_FUNC _CFFI_PYTHON_STARTUP_FUNC(const void *[]); /* forward */ static struct _cffi_pypy_init_s { const char *name; void (*func)(const void *[]); const char *code; } _cffi_pypy_init = { _CFFI_MODULE_NAME, (void(*)(const void *[]))_CFFI_PYTHON_STARTUP_FUNC, _CFFI_PYTHON_STARTUP_CODE, }; extern int pypy_carefully_make_gil(const char *); extern int pypy_init_embedded_cffi_module(int, struct _cffi_pypy_init_s *); static int _cffi_carefully_make_gil(void) { return pypy_carefully_make_gil(_CFFI_MODULE_NAME); } static int _cffi_initialize_python(void) { return pypy_init_embedded_cffi_module(0xB011, &_cffi_pypy_init); } /********** end PyPy-specific section **********/ #endif #ifdef __GNUC__ __attribute__((noinline)) #endif static _cffi_call_python_fnptr _cffi_start_python(void) { /* Delicate logic to initialize Python. This function can be called multiple times concurrently, e.g. when the process calls its first ``extern "Python"`` functions in multiple threads at once. It can also be called recursively, in which case we must ignore it. We also have to consider what occurs if several different cffi-based extensions reach this code in parallel threads---it is a different copy of the code, then, and we can't have any shared global variable unless it comes from 'libpythonX.Y.so'. Idea: * _cffi_carefully_make_gil(): "carefully" call PyEval_InitThreads() (possibly with Py_InitializeEx() first). * then we use a (local) custom lock to make sure that a call to this cffi-based extension will wait if another call to the *same* extension is running the initialization in another thread. It is reentrant, so that a recursive call will not block, but only one from a different thread. * then we grab the GIL and (Python 2) we call Py_InitializeEx(). At this point, concurrent calls to Py_InitializeEx() are not possible: we have the GIL. * do the rest of the specific initialization, which may temporarily release the GIL but not the custom lock. Only release the custom lock when we are done. */ static char called = 0; if (_cffi_carefully_make_gil() != 0) return NULL; _cffi_acquire_reentrant_mutex(); /* Here the GIL exists, but we don't have it. We're only protected from concurrency by the reentrant mutex. */ /* This file only initializes the embedded module once, the first time this is called, even if there are subinterpreters. */ if (!called) { called = 1; /* invoke _cffi_initialize_python() only once, but don't set '_cffi_call_python' right now, otherwise concurrent threads won't call this function at all (we need them to wait) */ if (_cffi_initialize_python() == 0) { /* now initialization is finished. Switch to the fast-path. */ /* We would like nobody to see the new value of '_cffi_call_python' without also seeing the rest of the data initialized. However, this is not possible. But the new value of '_cffi_call_python' is the function 'cffi_call_python()' from _cffi_backend. So: */ cffi_write_barrier(); /* ^^^ we put a write barrier here, and a corresponding read barrier at the start of cffi_call_python(). This ensures that after that read barrier, we see everything done here before the write barrier. */ assert(_cffi_call_python_org != NULL); _cffi_call_python = (_cffi_call_python_fnptr)_cffi_call_python_org; } else { /* initialization failed. Reset this to NULL, even if it was already set to some other value. Future calls to _cffi_start_python() are still forced to occur, and will always return NULL from now on. */ _cffi_call_python_org = NULL; } } _cffi_release_reentrant_mutex(); return (_cffi_call_python_fnptr)_cffi_call_python_org; } static void _cffi_start_and_call_python(struct _cffi_externpy_s *externpy, char *args) { _cffi_call_python_fnptr fnptr; int current_err = errno; #ifdef _MSC_VER int current_lasterr = GetLastError(); #endif fnptr = _cffi_start_python(); if (fnptr == NULL) { fprintf(stderr, "function %s() called, but initialization code " "failed. Returning 0.\n", externpy->name); memset(args, 0, externpy->size_of_result); } #ifdef _MSC_VER SetLastError(current_lasterr); #endif errno = current_err; if (fnptr != NULL) fnptr(externpy, args); } /* The cffi_start_python() function makes sure Python is initialized and our cffi module is set up. It can be called manually from the user C code. The same effect is obtained automatically from any dll-exported ``extern "Python"`` function. This function returns -1 if initialization failed, 0 if all is OK. */ _CFFI_UNUSED_FN static int cffi_start_python(void) { if (_cffi_call_python == &_cffi_start_and_call_python) { if (_cffi_start_python() == NULL) return -1; } cffi_read_barrier(); return 0; } #undef cffi_compare_and_swap #undef cffi_write_barrier #undef cffi_read_barrier #ifdef __cplusplus } #endif