Issue #13146: Writing a pyc file is now atomic under POSIX.
diff --git a/Python/import.c b/Python/import.c
index 6e3e0f1..0db7e43 100644
--- a/Python/import.c
+++ b/Python/import.c
@@ -1284,7 +1284,8 @@
#ifdef MS_WINDOWS
int fd;
#else
- PyObject *cpathbytes;
+ PyObject *cpathbytes, *cpathbytes_tmp;
+ Py_ssize_t cpathbytes_len;
#endif
PyObject *dirname;
Py_UCS4 *dirsep;
@@ -1345,13 +1346,25 @@
else
fp = NULL;
#else
+ /* Under POSIX, we first write to a tmp file and then take advantage
+ of atomic renaming. */
cpathbytes = PyUnicode_EncodeFSDefault(cpathname);
if (cpathbytes == NULL) {
PyErr_Clear();
return;
}
+ cpathbytes_len = PyBytes_GET_SIZE(cpathbytes);
+ cpathbytes_tmp = PyBytes_FromStringAndSize(NULL, cpathbytes_len + 4);
+ if (cpathbytes_tmp == NULL) {
+ Py_DECREF(cpathbytes);
+ PyErr_Clear();
+ return;
+ }
+ memcpy(PyBytes_AS_STRING(cpathbytes_tmp), PyBytes_AS_STRING(cpathbytes),
+ cpathbytes_len);
+ memcpy(PyBytes_AS_STRING(cpathbytes_tmp) + cpathbytes_len, ".tmp", 4);
- fp = open_exclusive(PyBytes_AS_STRING(cpathbytes), mode);
+ fp = open_exclusive(PyBytes_AS_STRING(cpathbytes_tmp), mode);
#endif
if (fp == NULL) {
if (Py_VerboseFlag)
@@ -1359,6 +1372,7 @@
"# can't create %R\n", cpathname);
#ifndef MS_WINDOWS
Py_DECREF(cpathbytes);
+ Py_DECREF(cpathbytes_tmp);
#endif
return;
}
@@ -1366,6 +1380,11 @@
/* First write a 0 for mtime */
PyMarshal_WriteLongToFile(0L, fp, Py_MARSHAL_VERSION);
PyMarshal_WriteObjectToFile((PyObject *)co, fp, Py_MARSHAL_VERSION);
+ fflush(fp);
+ /* Now write the true mtime */
+ fseek(fp, 4L, 0);
+ assert(mtime < LONG_MAX);
+ PyMarshal_WriteLongToFile((long)mtime, fp, Py_MARSHAL_VERSION);
if (fflush(fp) != 0 || ferror(fp)) {
if (Py_VerboseFlag)
PySys_FormatStderr("# can't write %R\n", cpathname);
@@ -1374,20 +1393,28 @@
#ifdef MS_WINDOWS
(void)DeleteFileW(PyUnicode_AS_UNICODE(cpathname));
#else
- (void) unlink(PyBytes_AS_STRING(cpathbytes));
+ (void) unlink(PyBytes_AS_STRING(cpathbytes_tmp));
Py_DECREF(cpathbytes);
+ Py_DECREF(cpathbytes_tmp);
#endif
return;
}
-#ifndef MS_WINDOWS
- Py_DECREF(cpathbytes);
-#endif
- /* Now write the true mtime */
- fseek(fp, 4L, 0);
- assert(mtime < LONG_MAX);
- PyMarshal_WriteLongToFile((long)mtime, fp, Py_MARSHAL_VERSION);
- fflush(fp);
fclose(fp);
+ /* Under POSIX, do an atomic rename */
+#ifndef MS_WINDOWS
+ if (rename(PyBytes_AS_STRING(cpathbytes_tmp),
+ PyBytes_AS_STRING(cpathbytes))) {
+ if (Py_VerboseFlag)
+ PySys_FormatStderr("# can't write %R\n", cpathname);
+ /* Don't keep tmp file */
+ unlink(PyBytes_AS_STRING(cpathbytes_tmp));
+ Py_DECREF(cpathbytes);
+ Py_DECREF(cpathbytes_tmp);
+ return;
+ }
+ Py_DECREF(cpathbytes);
+ Py_DECREF(cpathbytes_tmp);
+#endif
if (Py_VerboseFlag)
PySys_FormatStderr("# wrote %R\n", cpathname);
}