--- Python-2.5.1/Python/import.c.atomic	2007-08-08 20:51:41.313394000 -0400

+++ Python-2.5.1/Python/import.c	2007-08-08 21:01:57.640451000 -0400

@@ -858,19 +858,28 @@

 /* 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, time_t mtime)

 {

 	FILE *fp;

+	char *tmppathname;

-	fp = open_exclusive(cpathname);

+	/* 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);

 	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);

@@ -879,10 +888,11 @@

 	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 */

@@ -891,8 +901,30 @@

 	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);

 }