BUG: NMAKE May Incorrectly Think Targets are up to Date

ID: Q111769

The information in this article applies to:

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

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

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