Q111769: BUG: NMAKE May Incorrectly Think Targets are up to Date

Article: Q111769
Product(s): Microsoft Programming Utilities
Version(s): 
Operating System(s): 
Keyword(s): 
Last Modified: 08-OCT-1999

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The information in this article applies to:

- Microsoft NMAKE Utility for MS-DOS 
- Microsoft NMAKE Utility for Windows NT 
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SYMPTOMS
========

Running NMAKE on a very fast computer system and using the /B switch may not
force NMAKE to build a target if the target has the same time stamp as it's
dependent files.

RESOLUTION
==========

The build process may need to be modified so that a target is deleted when
it[ASCII 146]s dependents are updated. This could be done in the command block
for the dependents.

STATUS
======

Microsoft has confirmed this to be a problem in NMAKE versions 1.3, 1.4, and
1.5. We are researching this problem and will post new information here in the
Microsoft Knowledge Base as it becomes available.

MORE INFORMATION
================

The /B switch tells NMAKE to execute a dependency even if time stamps are equal.
However, on very fast systems, NMAKE may incorrectly determine that a target is
up to date, even when the /B switch is used. The following information is taken
from NMAKE.WRI from the MSVC\HELP directory:

"/B Tells NMAKE to execute a dependency even if time stamps are equal. Most
operating systems assign time stamps with a resolution of 2 seconds. If your
commands execute quickly, NMAKE may conclude that a file is up-to-date when in
fact it is not. This option may result in some unnecessary build steps but is
recommended when running NMAKE on very fast systems."

The sample below shows that on very fast system, the reverse case can occur, and
that some build steps may not be executed.

The makefile and looping batch file shown below can be used to illustrate this
behavior. When the looping batch file is executed, the following output should
be repeatedly generated:

  del target1
  del target2
  del target3
  echo "target2" > target2
  echo "target3" > target3
  echo "Creating target1!" > target1

  del target2
  del target3
  echo "target2" > target2
  echo "target3" > target3
  echo "Creating target1!" > target1

However, on a very fast machine, the following output is periodically generated:

  del target1
  del target2
  del target3
  echo "target2" > target2
  echo "target3" > target3
  echo "Creating target1!" > target1

  del target2
  del target3
  echo "target2" > target2
  echo "target3" > target3
  'target1' is up-to-date

Using the makefile shown below it is not possible for target1 to be up to date
since both of it[ASCII 146]s dependents were deleted and recreated after target1
already existed. The file target1 would have to have a time stamp that was at
least equal to the time stamp for it[ASCII 146]s dependents. Since NMAKE was
invoked with the /B switch, target1 should have been rebuilt. The batch file may
need to be run at least 10-20 times for the problem to show up. It may also be
necessary to supress output from NMAKE and the batch file in order to allow
NMAKE to run fast enough to reproduce the problem.

Sample Makefile
---------------

  target1: target2 target3
      echo "Creating target1!" > target1

  target2:
      echo "target2" > target2

  target3:
      echo "target3" > target3

  clean:
      del target2
      del target3

  reset:
      del target1
      del target2
      del target3

Looping Batch File
------------------

  :start
  nmake /B reset target1
  nmake /B clean target1
  goto start:

Additional query words: 1.30 1.40 1.50

======================================================================
Keywords          :  
Technology        : kbVCsearch kbAudDeveloper kbNMAKESearch
Version           : :

=============================================================================

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