Index: Objects/fileobject.c
===================================================================
--- Objects/fileobject.c    (revision 82848)
+++ Objects/fileobject.c    (working copy)
@@ -234,10 +234,36 @@
     return 0;
 }
 
+#if 1 /* DEBUG */
+
+#define DEBUG_ENTER(func_) \
+    const char *func = func_; \
+    const int thread = GetCurrentThreadId(); \
+    printf("thread(%4d) func(%s): enter....\n", GetCurrentThreadId(), func); \
+    fflush(stdout);
+
+#define DEBUG(s, file) \
+    assert(file); \
+    printf("thread(%4d) func(%s): file(%p) address(%p): " ## s ## "\n", GetCurrentThreadId(), func, file, file->f_setbuf); \
+    fflush(stdout);
+
+#define DEBUG_LEAVE \
+    printf("thread(%4d) func(%s): leave....\n", GetCurrentThreadId(), func); \
+    fflush(stdout);
+
+#else /* DEBUG */
+
+#define DEBUG_ENTER(func_)
+#define DEBUG(s, file)
+#define DEBUG_LEAVE
+
+#endif
+
 static PyObject *
 open_the_file(PyFileObject *f, char *name, char *mode)
 {
     char *newmode;
+    DEBUG_ENTER("open_the_file")
     assert(f != NULL);
     assert(PyFile_Check(f));
 #ifdef MS_WINDOWS
@@ -253,6 +279,7 @@
     newmode = PyMem_MALLOC(strlen(mode) + 3);
     if (!newmode) {
         PyErr_NoMemory();
+        DEBUG_LEAVE
         return NULL;
     }
     strcpy(newmode, mode);
@@ -284,6 +311,7 @@
             f->f_fp = _wfopen(PyUnicode_AS_UNICODE(f->f_name),
                               PyUnicode_AS_UNICODE(wmode));
             FILE_END_ALLOW_THREADS(f)
+            DEBUG("_wfopen", f);
         }
         Py_XDECREF(wmode);
     }
@@ -292,6 +320,7 @@
         FILE_BEGIN_ALLOW_THREADS(f)
         f->f_fp = fopen(name, newmode);
         FILE_END_ALLOW_THREADS(f)
+        DEBUG("fopen", f);
     }
 
     if (f->f_fp == NULL) {
@@ -342,6 +371,7 @@
     int sts = 0;
     int (*local_close)(FILE *);
     FILE *local_fp = f->f_fp;
+    DEBUG_ENTER("close_the_file")
     if (local_fp != NULL) {
         local_close = f->f_close;
         if (local_close != NULL && f->unlocked_count > 0) {
@@ -358,6 +388,7 @@
                     "PyFileObject locking error in "
                     "destructor (refcnt <= 0 at close).");
             }
+            DEBUG_LEAVE
             return NULL;
         }
         /* NULL out the FILE pointer before releasing the GIL, because
@@ -365,16 +396,23 @@
          * called. */
         f->f_fp = NULL;
         if (local_close != NULL) {
+            DEBUG("local_close enter...", f);
             Py_BEGIN_ALLOW_THREADS
             errno = 0;
             sts = (*local_close)(local_fp);
             Py_END_ALLOW_THREADS
-            if (sts == EOF)
+            DEBUG("local_close leave...", f);
+            if (sts == EOF) {
+                DEBUG_LEAVE
                 return PyErr_SetFromErrno(PyExc_IOError);
-            if (sts != 0)
+            }
+            if (sts != 0) {
+                DEBUG_LEAVE
                 return PyInt_FromLong((long)sts);
+            }
         }
     }
+    DEBUG_LEAVE
     Py_RETURN_NONE;
 }
 
@@ -416,6 +454,7 @@
 PyFile_SetBufSize(PyObject *f, int bufsize)
 {
     PyFileObject *file = (PyFileObject *)f;
+    DEBUG_ENTER("PyFile_SetBufSize")
     if (bufsize >= 0) {
         int type;
         switch (bufsize) {
@@ -437,11 +476,14 @@
         }
         fflush(file->f_fp);
         if (type == _IONBF) {
+            DEBUG("PyMem_Free", file);
             PyMem_Free(file->f_setbuf);
             file->f_setbuf = NULL;
         } else {
+            DEBUG("PyMem_Realloc enter", file);
             file->f_setbuf = (char *)PyMem_Realloc(file->f_setbuf,
                                                     bufsize);
+            DEBUG("PyMem_Realloc leave", file);
         }
 #ifdef HAVE_SETVBUF
         setvbuf(file->f_fp, file->f_setbuf, type, bufsize);
@@ -449,6 +491,7 @@
         setbuf(file->f_fp, file->f_setbuf);
 #endif /* !HAVE_SETVBUF */
     }
+    DEBUG_LEAVE
 }
 
 /* Set the encoding used to output Unicode strings.
@@ -520,6 +563,7 @@
 file_dealloc(PyFileObject *f)
 {
     PyObject *ret;
+    DEBUG_ENTER("file_dealloc")
     if (f->weakreflist != NULL)
         PyObject_ClearWeakRefs((PyObject *) f);
     ret = close_the_file(f);
@@ -530,6 +574,7 @@
     else {
         Py_DECREF(ret);
     }
+    DEBUG("PyMem_Free", f);
     PyMem_Free(f->f_setbuf);
     Py_XDECREF(f->f_name);
     Py_XDECREF(f->f_mode);
@@ -537,6 +582,7 @@
     Py_XDECREF(f->f_errors);
     drop_readahead(f);
     Py_TYPE(f)->tp_free((PyObject *)f);
+    DEBUG_LEAVE
 }
 
 static PyObject *
@@ -567,11 +613,15 @@
 static PyObject *
 file_close(PyFileObject *f)
 {
-    PyObject *sts = close_the_file(f);
+    PyObject *sts;
+    DEBUG_ENTER("file_close")
+    sts = close_the_file(f);
     if (sts) {
+        DEBUG("PyMem_Free", f);
         PyMem_Free(f->f_setbuf);
         f->f_setbuf = NULL;
     }
+    DEBUG_LEAVE
     return sts;
 }