-        path_src="$(cut -d $'\n' -f1 < <(echo "$item"))";
-        path_prf="$(cut -d $'\n' -f2 < <(echo "$item"))";
-        path_src_sesc="${path_src//\"/\\\"}"; # escape path double quotes. See [4].
-        path_prf_sesc="${path_prf//\"/\\\"}"; # escape path double quotes. See [4].
-        if [[ -z "$path_src" ]] || [[ -z "$path_prf" ]]; then
-            yell "ERROR:blank verify item encountered. Skipping:item:$item";
-            continue;
-        fi;
-        vbm "DEBUG:Attempting to verify source file:path_src:$path_src";
-        vbm "DEBUG:    against proof file:          path_prf:$path_prf";
-        if [[ ! $option_dry_run == "true" ]]; then
-            ### Try verify with known calendars in random order
-            while read -r url; do
-                vbm "DEBUG:Verifying with calendar:url:$url";
-                if [[ "$opVerbose" = "true" ]]; then
-                    commands+=("cmdwrap ots -v -l $url --no-default-whitelist verify -f \"$path_src_sesc\" \"$path_prf_sesc\"") && break;
-                else
-                    commands+=("cmdwrap ots -l $url --no-default-whitelist verify -f \"$path_src_sesc\" \"$path_prf_sesc\"") && break;
-                fi;
-                #ots -l "$url" --no-default-whitelist verify -f "$path_src" "$path_prf" && break;
-            done < <(printf "%s\n" "${calendars[@]}" | shuf);
-        else
-            yell "DEBUG:DRY RUN:Not running:\"ots verify -f $path_src $path_prf\"";
-        fi;
+        wait_for_jobslot && {
+            path_src="$(cut -d $'\n' -f1 < <(echo "$item"))";
+            path_prf="$(cut -d $'\n' -f2 < <(echo "$item"))";
+            if [[ -z "$path_src" ]] || [[ -z "$path_prf" ]]; then
+                yell "ERROR:blank verify item encountered. Skipping:item:$item";
+                return 1; # would have been `continue` were it not in a subshell
+            fi;
+            vbm "DEBUG:Attempting to verify source file:path_src:$path_src";
+            vbm "DEBUG:    against proof file:          path_prf:$path_prf";
+            if [[ ! $option_dry_run == "true" ]]; then
+                ### Try verify with known calendars in random order
+                while read -r url; do
+                    vbm "DEBUG:Verifying with calendar:url:$url";
+
+                    #### assemble command
+                    local -a cmd_temp;
+                    cmd_temp=("ots");
+                    if [[ "$opVerbose" = "true" ]]; then cmd_temp+=("-v"); fi;
+                    cmd_temp+=("-l" "$url" "--no-default-whitelist");
+                    cmd_temp+=("verify" "-f" "$path_src" "$path_prf");
+                    if [[ "$opVerbose" = "true" ]]; then declare -p cmd_temp; fi;
+
+                    #### execute command
+                    "${cmd_temp[@]}";
+                    unset cmd_temp;
+                    break;
+                    #ots -l "$url" --no-default-whitelist verify -f "$path_src" "$path_prf" && break;
+                done < <(printf "%s\n" "${calendars[@]}" | shuf);
+            else
+                yell "DEBUG:DRY RUN:Not running:\"ots verify -f $path_src $path_prf\"";
+            fi;
+        } &