On Unix, use O_EXCL when creating the .pyc/.pyo files, to avoid a race condition
diff --git a/Python/import.c b/Python/import.c
index 9d65c70..533f85e 100644
--- a/Python/import.c
+++ b/Python/import.c
@@ -28,12 +28,17 @@
#ifndef DONT_HAVE_SYS_TYPES_H
#include <sys/types.h>
#endif
+
#ifndef DONT_HAVE_SYS_STAT_H
#include <sys/stat.h>
#elif defined(HAVE_STAT_H)
#include <stat.h>
#endif
+#ifdef HAVE_FCNTL_H
+#include <fcntl.h>
+#endif
+
#if defined(PYCC_VACPP)
/* VisualAge C/C++ Failed to Define MountType Field in sys/stat.h */
#define S_IFMT (S_IFDIR|S_IFCHR|S_IFREG)
@@ -627,6 +632,31 @@
}
+/* Helper to open a bytecode file for writing in exclusive mode */
+
+static FILE *
+open_exclusive(char *filename)
+{
+#if defined(O_EXCL)&&defined(O_CREAT)&&defined(O_WRONLY)&&defined(O_TRUNC)
+ /* Use O_EXCL to avoid a race condition when another process tries to
+ write the same file. When that happens, our open() call fails,
+ which is just fine (since it's only a cache).
+ XXX If the file exists and is writable but the directory is not
+ writable, the file will never be written. Oh well.
+ */
+ int fd;
+ (void) unlink(filename);
+ fd = open(filename, O_EXCL|O_CREAT|O_WRONLY|O_TRUNC, 0666);
+ if (fd < 0)
+ return NULL;
+ return fdopen(fd, "wb");
+#else
+ /* Best we can do -- on Windows this can't happen anyway */
+ return fopen(filename, "wb");
+#endif
+}
+
+
/* 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
@@ -637,7 +667,7 @@
{
FILE *fp;
- fp = fopen(cpathname, "wb");
+ fp = open_exclusive(cpathname);
if (fp == NULL) {
if (Py_VerboseFlag)
PySys_WriteStderr(