Allow multiple instances of sbopkg to run simultaneously.

This patch makes it possible to run multiple sbopkg instances
simultaneously in different $SBOPKGTMP prefixes.
There are some known (and possibly unknown) caveats the user
should be aware before enabling this option -- I documented the
ones I could think of.

Signed-off-by: Mauro Giachero <mauro.giachero@gmail.com>

ChangeLog-current.txt

@@ -17,4 +17,7 @@ enhancements:
     RHS of [[ commands using the =~ operator which broke the repo file
     validation, among other things. Thanks to SiegeX, Zmyrgel, and BCarey for
     the reports and suggestions.
+  * Add the ability to run multiple sbopkg instances simultaneously. This has
+    been suggested many times in the past. Users should read the sbopkg.conf
+    man page before using this option (which is disabled by default).
 +--------------------------+

src/etc/sbopkg/sbopkg.conf.new

@@ -20,6 +20,11 @@ LOGFILE=$LOGDIR/sbopkg-build-log
 DEBUG=0
 CLEANUP=NO
 
+# Set this to YES to allow multiple instances of sbopkg to run.
+# Please read the sbopkg.conf(5) man page before doing so
+# (otherwise, don't even think about submitting a problem report).
+ALLOW_MULTI=NO
+
 # The following variables are used by sbopkg and by the SlackBuild scripts
 # themselves.  They are exported for this reason.
 export TMP=${TMP:-/tmp/SBo}

src/usr/man/man5/sbopkg.conf.5

@@ -138,6 +138,40 @@ from the environment or from the configuration files is ignored.
 
 The default value of CLEANUP is: NO.
 
+.TP 5
+.B ALLOW_MULTI
+.br
+When set to YES, this option allows the user to run multiple instances
+of sbopkg.
+
+Please understand that this option is provided for convenience, but
+given the number of potential issues you can face when enabling this
+(and we aren't going to try to work around users doing silly things),
+you should consider working with ALLOW_MULTI=YES as an EXPERIMENTAL
+UNSUPPORTED feature. If you encounter problems, please try to make sure
+these aren't caused by yourself doing improper things.
+
+For reference, these are some of the things you shouldn't do with this
+option enabled:
+.RS 6
+.IP \[bu] 2
+run an ALLOW_MULTI=NO instance together with one or more having
+ALLOW_MULTI=YES
+.IP \[bu]
+sync a repository when another instance is using it
+.IP \[bu]
+change the branch of a git repository when another instance is using it
+(you can do this with rsync -- i.e. SlackBuild.org -- repos)
+.IP \[bu]
+simultaneously build or install the same package from different instances
+.IP \[bu]
+save a queue file while using it from another instance
+.RE
+
+.RS 5
+There can be more unsafe situations we haven't thought about. Take care.
+.RE
+
 .TP 5
 .B DEBUG
 .br

src/usr/sbin/sbopkg

@@ -106,7 +106,7 @@ config_check() {
     # Some configuration options are mandatory
     for VAR in REPO_ROOT LOGDIR QUEUEDIR SRCDIR SBOPKGTMP REPO_NAME \
         REPO_BRANCH KEEPLOG CLEANUP LOGFILE DEBUG TMP OUTPUT RSYNCFLAGS \
-        WGETFLAGS DIFF DIFFOPTS SBOPKG_REPOS_D; do
+        WGETFLAGS DIFF DIFFOPTS SBOPKG_REPOS_D ALLOW_MULTI; do
         if [[ -z "${!VAR}" ]]; then
             MISSING+="$VAR "
         fi
@@ -141,6 +141,22 @@ EOF
     if [[ $CLEANUP == [Nn][Oo] ]]; then
         unset CLEANUP
     fi
+    if [[ $ALLOW_MULTI == [Nn][Oo] ]]; then
+        unset ALLOW_MULTI
+    fi
+
+    # If multiple instances of sbopkg are allowed, they need their own
+    # private $SBOPKGTMP.
+    # Since simply appending the cookie makes sbopkg to inform the user about
+    # the creation of the new $SBOPKGTMP directory on every startup, we do a
+    # little more setup here.
+    if [[ $ALLOW_MULTI ]]; then
+        # Note: this ck_dir line is copied from directory_checks
+        ck_dir $SBOPKGTMP \
+            "Creating local sbopkg TMP directory $SBOPKGTMP."
+        SBOPKGTMP+=/sbopkg-instance-$(mcookie)
+        mkdir -p $SBOPKGTMP
+    fi
 
     # Make sure there are no unexpected files in $SBOPKGTMP
     if [[ -n $(find $SBOPKGTMP -mindepth 1 -maxdepth 1 -not -name sbopkg\* \
@@ -294,7 +310,7 @@ directory_checks() {
     ck_dir $SBOPKGTMP \
         "Creating local sbopkg TMP directory $SBOPKGTMP."
     ck_dir $TMP \
-        "Creating local SBo TMP directory $TMP."
+        "Creating local SBo TMP directory $TMP." # Also see config_check()
     ck_dir $OUTPUT \
         "Creating local package output directory $OUTPUT."
 
@@ -3873,6 +3889,23 @@ cleanup() {
     rm -f $SBOPKGTMP/sbopkg-tmp-*
     rm -f $PIDFILE
 
+    if [[ $ALLOW_MULTI ]]; then
+        if ! rmdir $SBOPKGTMP 2>/dev/null; then
+            cat <<EOF
+$SCRIPT was unable to remove the temporary folder:
+
+$SBOPKGTMP
+
+since it still contains some file or directory.
+Please file a bug report telling us how you managed to trigger this
+message and append to it the output of:
+
+find $SBOPKGTMP
+
+EOF
+        fi
+    fi
+
     # Back to the directory the user started sbopkg in
     cd "$CWD"
 }
@@ -4290,7 +4323,7 @@ fi
 directory_checks
 
 # Check for another instance
-pid_check
+[[ $ALLOW_MULTI ]] || pid_check
 
 if [[ $DIAG ]]; then
     if [[ $TERM =~ ^rxvt.* || $TERM =~ ^screen.* ]]; then