nixpkgs/pkgs/development/interpreters/python/cpython/2.7/atomic_pyc.patch

diff --git a/Lib/py_compile.py b/Lib/py_compile.py
index 978da73d74..3559eb95ca 100644
--- a/Lib/py_compile.py
+++ b/Lib/py_compile.py
@@ -120,16 +120,27 @@ def compile(file, cfile=None, dfile=None, doraise=False):
             return
     if cfile is None:
         cfile = file + (__debug__ and 'c' or 'o')
-    with open(cfile, 'wb') as fc:
-        fc.write('\0\0\0\0')
-        if "DETERMINISTIC_BUILD" in os.environ:
+    # Atomically write the pyc/pyo file.  Issue #13146.
+    # id() is used to generate a pseudo-random filename.
+    path_tmp = '{}.{}'.format(cfile, id(cfile))
+    try:
+        with open(path_tmp, 'wb') as fc:
             fc.write('\0\0\0\0')
-        else:
-            wr_long(fc, timestamp)
-        marshal.dump(codeobject, fc)
-        fc.flush()
-        fc.seek(0, 0)
-        fc.write(MAGIC)
+            if "DETERMINISTIC_BUILD" in os.environ:
+                fc.write('\0\0\0\0')
+            else:
+                wr_long(fc, timestamp)
+            marshal.dump(codeobject, fc)
+            fc.flush()
+            fc.seek(0, 0)
+            fc.write(MAGIC)
+        os.rename(path_tmp, cfile)
+    except OSError:
+        try:
+            os.unlink(path_tmp)
+        except OSError:
+            pass
+        raise
 
 def main(args=None):
     """Compile several source files.
diff --git a/Python/import.c b/Python/import.c
index 1e31d79279..f78a1efcf0 100644
--- a/Python/import.c
+++ b/Python/import.c
@@ -951,6 +951,8 @@ static void
 write_compiled_module(PyCodeObject *co, char *cpathname, struct stat *srcstat, time_t mtime)
 {
     FILE *fp;
+    size_t cpathname_len;
+    char *cpathname_tmp;
 #ifdef MS_WINDOWS   /* since Windows uses different permissions  */
     mode_t mode = srcstat->st_mode & ~S_IEXEC;
     /* Issue #6074: We ensure user write access, so we can delete it later
@@ -963,11 +965,28 @@ write_compiled_module(PyCodeObject *co, char *cpathname, struct stat *srcstat, t
     mode_t mode = srcstat->st_mode & ~S_IXUSR & ~S_IXGRP & ~S_IXOTH;
 #endif
 
+#ifdef MS_WINDOWS
     fp = open_exclusive(cpathname, mode);
+#else
+    /* Under POSIX, we first write to a tmp file and then take advantage
+       of atomic renaming. */
+    cpathname_len = strlen(cpathname);
+    cpathname_tmp = PyMem_MALLOC(cpathname_len + 5);
+    if (cpathname_tmp == NULL) {
+        PyErr_Clear();
+        return;
+    }
+    memcpy(cpathname_tmp, cpathname, cpathname_len);
+    memcpy(cpathname_tmp + cpathname_len, ".tmp", 5);
+    fp = open_exclusive(cpathname_tmp, mode);
+#endif
     if (fp == NULL) {
         if (Py_VerboseFlag)
             PySys_WriteStderr(
                 "# can't create %s\n", cpathname);
+#ifndef MS_WINDOWS
+        PyMem_FREE(cpathname_tmp);
+#endif
         return;
     }
     PyMarshal_WriteLongToFile(pyc_magic, fp, Py_MARSHAL_VERSION);
@@ -979,7 +998,12 @@ write_compiled_module(PyCodeObject *co, char *cpathname, struct stat *srcstat, t
             PySys_WriteStderr("# can't write %s\n", cpathname);
         /* Don't keep partial file */
         fclose(fp);
+#ifdef MS_WINDOWS
         (void) unlink(cpathname);
+#else
+        (void) unlink(cpathname_tmp);
+        PyMem_FREE(cpathname_tmp);
+#endif
         return;
     }
     /* Now write the true mtime (as a 32-bit field) */
@@ -989,6 +1013,19 @@ write_compiled_module(PyCodeObject *co, char *cpathname, struct stat *srcstat, t
         PyMarshal_WriteLongToFile((long)mtime, fp, Py_MARSHAL_VERSION);
         fflush(fp);
     }
+    /* Under POSIX, do an atomic rename */
+#ifndef MS_WINDOWS
+    if (rename(cpathname_tmp, cpathname)) {
+        if (Py_VerboseFlag)
+            PySys_WriteStderr("# can't write %s\n", cpathname);
+        /* Don't keep tmp file */
+        fclose(fp);
+        (void) unlink(cpathname_tmp);
+        PyMem_FREE(cpathname_tmp);
+        return;
+    }
+    PyMem_FREE(cpathname_tmp);
+#endif
     fclose(fp);
     if (Py_VerboseFlag)
         PySys_WriteStderr("# wrote %s\n", cpathname);