Index: repy/emulfile.py
===================================================================
--- repy/emulfile.py	(revision 2330)
+++ repy/emulfile.py	(working copy)
@@ -16,6 +16,9 @@
 import os
 import idhelper

+# needed for locking the fileinfo hash
+import threading
+
 # I need to rename file so that the checker doesn't complain...
 myfile = file

@@ -72,10 +75,18 @@
   # Handle the case where the file is open via an exception to prevent the user
   # from removing a file to circumvent resource accounting

+  fileinfolock.acquire()
   for filehandle in fileinfo:
     if filename == fileinfo[filehandle]['filename']:
+      fileinfolock.release()
       raise Exception, 'File "'+filename+'" is open with handle "'+filehandle+'"'
-  return os.remove(filename)
+
+  try:
+    result = os.remove(filename)
+  finally:
+    fileinfolock.release()
+
+  return result



@@ -85,34 +96,129 @@
 def emulated_open(filename, mode="rb"):
   """
    <Purpose>
-      Allows the user program to open a file safely.   This function is meant
-      to resemble the builtin "open"
+      Allows the user program to open a file safely. This function is meant
+      to resemble the builtin "open".

    <Arguments>
       filename:
-         The file that should be operated on
+         The file that should be operated on.
       mode:
-         The mode (see open)
+         The mode (see open).

    <Exceptions>
-      As with open, this may raise a number of errors
+      As with open, this may raise a number of errors. Additionally:

+      TypeError if the mode is not a string.
+      ValueError if the modestring is invalid.
+
    <Side Effects>
-      Opens a file on disk, using a file descriptor.   When opened with "w"
+      Opens a file on disk, using a file descriptor. When opened with "w"
       it will truncate the existing file.

    <Returns>
+      A file-like object.
+  """
+
+  if type(mode) is not str:
+    raise TypeError("Attempted to open file with invalid mode (must be a string).")
+
+  # We just filter out 'b' / 't' in modestrings because emulated_file opens
+  # everything in binary mode for us.
+
+  originalmode = mode
+
+  if 'b' in mode:
+    mode = mode.replace('b','')
+
+  if 't' in mode:
+    mode = mode.replace('t','')
+
+  # Now we use our very safe, cross-platform open-like function and other
+  # file-object methods to emulate ANSI file modes.
+
+  file_object = None
+  if mode == "r":
+    file_object = safe_open(filename, "r")
+
+  elif mode == "r+":
+    file_object = safe_open(filename, "rw")
+
+  elif mode == "w" or mode == "w+":
+    file_object = safe_open(filename, "rw", create=True)
+    fileinfo[file_object.filehandle]['fobj'].truncate()
+
+  elif mode == "a" or mode == "a+":
+    file_object = safe_open(filename, "rw", create=True)
+    file_object.seek(0, os.SEEK_END)
+
+
+  if file_object is None:
+    raise ValueError("Invalid or unsupported mode ('%s') passed to open()." % originalmode)
+
+  return file_object
+
+
+
+
+def safe_open(filename, mode="r", create=False):
+  """
+   <Purpose>
+      Allows the user program to open a file safely.   This function is not
+      meant to resemble the builtin "open".
+
+   <Arguments>
+      filename:
+         The file that should be operated on
+      mode:
+         The mode:
+            "r":  Open the file for reading.
+            "rw": Open the file for reading and writing.
+
+            These are the only valid modes accepted by this version of
+            open(). Note: files are always opened in "binary" mode.
+      create:
+         If True, create the file if it doesn't exist already.
+
+   <Exceptions>
+      As with open, this may raise a number of errors. Additionally:
+
+      ValueError is raised if this is passed an invalid mode.
+
+   <Side Effects>
+      Opens a file on disk, using a file descriptor.
+
+   <Returns>
       A file-like object
   """

-  restrictions.assertisallowed('open',filename,mode)
+  # Only allow 'r', 'rw', and 'U'.

-  return emulated_file(filename, mode)
+  actual_mode = None
+  if mode == "r":
+    actual_mode = "rb"
+  elif mode == "rw":
+    actual_mode = "r+b"
+
+  if actual_mode is None:
+    raise ValueError("Valid modes for opening a file in repy are 'r' and 'rw'.")

+  restrictions.assertisallowed('open', filename, actual_mode)

+  if create and not os.path.exists(filename):
+    # Create a file by opening it in write mode and then closing it.
+    restrictions.assertisallowed('open', filename, "wb")

+    create_file = emulated_file(filename, "wb")
+    create_file.close()
+
+  return emulated_file(filename, actual_mode)
+
+
+
+
 # This keeps the state for the files (the actual objects, etc.)
 fileinfo = {}
+fileinfolock = threading.Lock()



@@ -171,15 +277,37 @@
       # It must have a 'b'
       mode = mode + 'b'

-    assert_is_allowed_filename(filename)
+    # Here we are checking that we only open a given file once in 'write' mode
+    # so that file access is more uniform across platforms. (On Microsoft
+    # Windows, for example, writing to the same file from two different file-
+    # handles throws an error because of the way Windows (by default) locks
+    # files opened for writing.)
+    fileinfolock.acquire()

-    self.filehandle = idhelper.getuniqueid()
+    try:
+      # Check the entire fileinfo dictionary for the same file already being
+      # open.
+      for fileinfokey in fileinfo.keys():

-    nanny.tattle_add_item('filesopened',self.filehandle)
+        # If the filename matches this one, raise an exception.
+        if os.path.abspath(fileinfo[fileinfokey]['filename']) == \
+            os.path.abspath(filename)
+          raise ArgumentError(\
+              "A file is only allowed to have one open filehandle.")

-    fileinfo[self.filehandle] = {'filename':filename, 'mode':mode,'fobj':myfile(filename,mode)}
-    self.name=filename
-    self.mode=mode
+      assert_is_allowed_filename(filename)
+
+      self.filehandle = idhelper.getuniqueid()
+
+      nanny.tattle_add_item('filesopened',self.filehandle)
+
+      fileinfo[self.filehandle] = {'filename':filename, 'mode':mode,'fobj':myfile(filename,mode)}
+      self.name=filename
+      self.mode=mode
+
+    finally:
+      fileinfolock.release()
+
     return None


@@ -203,11 +331,16 @@

     nanny.tattle_remove_item('filesopened',myfilehandle)

-    returnvalue = fileinfo[myfilehandle]['fobj'].close()
+    fileinfolock.acquire()
+    try:
+      returnvalue = fileinfo[myfilehandle]['fobj'].close()

-    # delete the filehandle
-    del fileinfo[myfilehandle]
+      # delete the filehandle
+      del fileinfo[myfilehandle]

+    finally:
+      fileinfolock.release()
+
     return returnvalue


Index: repy/tests/z_testopen.py
===================================================================
--- repy/tests/z_testopen.py	(revision 0)
+++ repy/tests/z_testopen.py	(revision 0)
@@ -0,0 +1,55 @@
+# Some tests to ensure open() behaves like our definition.
+
+SEEK_SET = 0    # Absolute
+SEEK_CUR = 1    # Relative
+SEEK_END = 2    # End of the file
+
+try:
+  # Test basic writing / reading
+  fro = open("junk_test.out", "w+")
+  fro.write("hi!")
+  fro.flush()
+  fro.seek(0, SEEK_SET)
+  contents = fro.read()
+  fro.close()
+  if contents != "hi!":
+    print "Failed to write to / read from file!"
+
+  fro = open("junk_test.out", "r")
+  contents = fro.read()
+  fro.close()
+  if contents != "hi!":
+    print "Failed to write to / read from file!"
+
+  # Test "w" semantics
+  fro = open("junk_test.out", "w+")
+  contents = fro.read()
+  if contents != "":
+    print "Write mode fails to truncate file!"
+  fro.seek(0, SEEK_SET)
+  fro.write("Testing 123")
+  fro.close()
+
+  # Test append
+  fro = open("junk_test.out", "a+")
+  fro.write("abc")
+  fro.flush()
+  fro.seek(0, SEEK_SET)
+  contents = fro.read()
+  fro.close()
+  if contents != "Testing 123abc":
+    print "Append mode fails to append!"
+
+  # Test universal newlines
+  fro = open("junk_test.out", "w+")
+  fro.write("Hello\rMac\r\nWindows\nUnix World!")
+  fro.close()
+  fro = open("junk_test.out", "rU")
+  contents = fro.read()
+  fro.close()
+  if contents != "Hello\nMac\nWindows\nUnix World!":
+    print "Universal readline mode fails to read universally!"
+
+finally:
+  if "junk_test.out" in listdir():
+    removefile("junk_test.out")