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Annotation of embedaddon/ntp/m4/ntp_cacheversion.m4, revision 1.1.1.1

1.1       misho       1: # NTP_CACHEVERSION(component, version)
                      2: # ------------------------------------
                      3: # compare this configure script's cache version stamp with the stamp
                      4: # saved by the prior run in config.cache.  If they differ, clear all
                      5: # cache variables to avoid using results cached with a script that
                      6: # is known to differ in a cache-invalidating manner.
                      7: #
                      8: # Note: use immediately following AC_INIT in configure.ac, as clearing
                      9: # all _cv_ variables only makes sense immediately after loading, before
                     10: # use or modification.
                     11: #
                     12: # It is assumed that parent configure.ac files which use
                     13: # AC_CONFIG_SUBDIR to invoke child configure.ac files have used 
                     14: # NTP_CACHEVERSION if any children do.  The top-level configure script
                     15: # will clear a previous cache lacking any saved cache version number,
                     16: # while children do not.  The reason is the children can rely on the
                     17: # parent having cleared any cache variables predating this mechanism.
                     18: # Therefore the child can rely on the config.cache generated by the
                     19: # parent on the first run despite not finding its version stamp
                     20: # previously saved.  In this case top-level means a configure script
                     21: # not invoked by another configure script in its parent directory.
                     22: 
                     23: AC_DEFUN_ONCE([NTP_CACHEVERSION], [
                     24:     AC_BEFORE([$0], [AM_INIT_AUTOMAKE])dnl
                     25:     AC_BEFORE([$0], [AM_CONFIG_HEADER])dnl
                     26:     AC_BEFORE([$0], [AC_PROG_CC])dnl
                     27:     AC_BEFORE([$0], [AC_CONFIG_SUBDIRS])dnl
                     28: 
                     29:     ntp_cache_flush=1
                     30:     
                     31:     case "$ntp_cv_[$1]_cache_version" in
                     32:      [$2])
                     33:        # same version, good
                     34:        ntp_cache_flush=0
                     35:        ;;
                     36:      '')
                     37:        # No cache, predates ntp_cv_$1_cache_version, or is empty.
                     38:        case "$cache_file" in
                     39:         /dev/null)
                     40:            ntp_cache_flush=0
                     41:            ;;
                     42:         *)
                     43:            case "$NTP_CACHEVERSION_PARENT" in
                     44:             '')
                     45:                # Do not clear the cache immediately after it is created
                     46:                # empty as it is noisy.  Differentiate a newly-created 
                     47:                # config.cache from one predating the cache version 
                     48:                # mechanism by looking for the first cached variable set 
                     49:                # by Autoconf
                     50:                case "$ac_cv_path_install" in
                     51:                 '')
                     52:                    # empty config.cache file
                     53:                    ntp_cache_flush=0
                     54:                esac
                     55:                ;;
                     56:             *)
                     57:                # Parent configure just created cache from empty,
                     58:                # flushing would be counterproductive.
                     59:                ntp_cache_flush=0;
                     60:            esac
                     61:        esac
                     62:        ;;
                     63:      *)
                     64:        # configure cache version mismatches config.cache version
                     65:     esac
                     66:     
                     67:     case "$ntp_cache_flush" in
                     68:      1)
                     69:        c_version="${ntp_cv_[$1]_cache_version:-(no version found)}"
                     70:        
                     71:        # Do we flush all variables or exclude others' version stamps?
                     72: 
                     73:        case "$NTP_CACHEVERSION_PARENT" in
                     74:         '')
                     75:            # Clear all *_cv_* variables including our child subdirs'
                     76:            # ntp_cv_*_cache_version variables.  This prevents subdir
                     77:            # configure scripts from noticing a version mismatch just
                     78:            # after the top configure in the invocation cleared and
                     79:            # recreated the cache.
                     80:        
                     81:            c_varname_list=`set |
                     82:                            sed -n -e 's/=.*$//' \
                     83:                                   -e '/_cv_/p'
                     84:                           `
                     85:            ;;
                     86:         *)
                     87:            # This is not the top configure this particular invocation.
                     88:            # Clear all *_cv_* variables sparing the version stamps
                     89:            # of other configure scripts, so we don't trigger
                     90:            # useless repeated clearings.
                     91: 
                     92:            c_varname_list=`set |
                     93:                            sed -n -e 's/=.*$//' \
                     94:                                   -e '/ntp_cv_.*_cache_version/d' \
                     95:                                   -e '/_cv_/p'
                     96:                           `
                     97:        esac
                     98:        
                     99:        for c_varname in $c_varname_list
                    100:        do
                    101:            AS_UNSET([$c_varname])
                    102:        done
                    103:        
                    104:        AC_MSG_NOTICE([[$cache_file saved by another version, ignored.]])
                    105:        AC_MSG_NOTICE([[configure script cache version: ]][$2])
                    106:        AC_MSG_NOTICE([[$cache_file version: $c_version]])
                    107:        AS_UNSET([c_varname])
                    108:        AS_UNSET([c_varname_list])
                    109:        AS_UNSET([c_version])
                    110:     esac
                    111: 
                    112:     AS_UNSET([ntp_cache_flush])
                    113: 
                    114:     # save configure version in config.cache for next time
                    115:     ntp_cv_[$1]_cache_version="[$2]"
                    116: 
                    117:     # let any subdir configure.ac NTP_CACHEVERSION invocations
                    118:     # know they are not the top level.
                    119:     NTP_CACHEVERSION_PARENT='[$1]' ; export NTP_CACHEVERSION_PARENT
                    120: ])dnl