--- Python-2.6.4/Python/import.c.import	2009-12-02 14:16:47.286400577 +1300

+++ Python-2.6.4/Python/import.c	2009-12-02 14:26:08.955429879 +1300

@@ -866,8 +866,9 @@

 /* Write a compiled module to a file, placing the time of last

    modification of its source into the header.

-   Errors are ignored, if a write error occurs an attempt is made to

-   remove the file. */

+   Write to a temporary file first so that creating the file is atomic.

+   Errors are ignored, if a write/unlink/rename error occurs an attempt

+   is made to remove the temporary file. */

 static void

 write_compiled_module(PyCodeObject *co, char *cpathname, struct stat *srcstat)

@@ -879,12 +880,21 @@

 #else

 	mode_t mode = srcstat->st_mode & ~S_IXUSR & ~S_IXGRP & ~S_IXOTH;

 #endif 

+	char *tmppathname;

+ 

+	/* the temporary file is called cpathname + ".tmp" */

+	if ((tmppathname = PyMem_Malloc(strlen(cpathname) + strlen(".tmp") + 1))

+		== NULL) {

+		return;

+	}

+	sprintf (tmppathname, "%s.tmp", cpathname);

+	fp = open_exclusive(tmppathname, mode);

-	fp = open_exclusive(cpathname, mode);

 	if (fp == NULL) {

 		if (Py_VerboseFlag)

 			PySys_WriteStderr(

-				"# can't create %s\n", cpathname);

+				"# can't create %s\n", tmppathname);

+		PyMem_Free(tmppathname);

 		return;

 	}

 	PyMarshal_WriteLongToFile(pyc_magic, fp, Py_MARSHAL_VERSION);

@@ -893,10 +903,11 @@

 	PyMarshal_WriteObjectToFile((PyObject *)co, fp, Py_MARSHAL_VERSION);

 	if (fflush(fp) != 0 || ferror(fp)) {

 		if (Py_VerboseFlag)

-			PySys_WriteStderr("# can't write %s\n", cpathname);

+			PySys_WriteStderr("# can't write %s\n", tmppathname);

 		/* Don't keep partial file */

 		fclose(fp);

-		(void) unlink(cpathname);

+		(void) unlink(tmppathname);

+		PyMem_Free(tmppathname);

 		return;

 	}

 	/* Now write the true mtime */

@@ -905,8 +916,30 @@

 	PyMarshal_WriteLongToFile((long)mtime, fp, Py_MARSHAL_VERSION);

 	fflush(fp);

 	fclose(fp);

+	/* Delete the old compiled file, if exists */

+	if (unlink (cpathname)) {

+		if ((errno != ENOENT)) {

+			/* the file exists but could not be deleted */

+			if (Py_VerboseFlag)

+				PySys_WriteStderr(

+					"# can't unlink %s\n", cpathname);

+			(void) unlink(tmppathname);

+			PyMem_Free(tmppathname);

+			return;

+		}

+	}

+	/* rename the tmp file to the real file name */

+	if (rename (tmppathname, cpathname)) {

+		if (Py_VerboseFlag)

+			PySys_WriteStderr(

+				"# can't rename %s to %s\n", tmppathname, cpathname);

+		(void) unlink(tmppathname);

+		PyMem_Free(tmppathname);

+		return;

+	}

 	if (Py_VerboseFlag)

 		PySys_WriteStderr("# wrote %s\n", cpathname);

+	PyMem_Free(tmppathname);

 }

 static void