Changeset 35415

Timestamp:

2021-09-17T16:41:40+12:00 (3 years ago)

Author:

kjdon

Message:

OpenOfficeConverter.pm's BEGIN block running soffice in the background on windows using start, ended up causing GLI to hang (cmdline building didn't hang). It was because of the join() calls on the perl process' stdout/stderr in Safeprocess.InputStreamGobblers() hanging because no eof/eos was received. soffice or other silent external programs launched through perl using system() kept stderr/stdout open even though the external program was supposedly launched in the background. After lots of investigation, Dr Bainbridge found that unlike the system() command in perl/C/C++, Java programs using Runtime.exec() and WScriptHost/CScriptHost script files (like VBScript) can launch external programs fully in the background so that this hanging in GLI doesn't occur. Dr Bainbridge decided we should go with a custom VBScript, created in background-launcher.vbs (committed previously, revision 35414) instead of a Java Program as compiling and setting JAVA_HOME or updating PATH not necessary.

Location:

gs2-extensions/open-office/trunk

Files:

• open-office-java.tar.gz (modified) ( previous)
• open-office-java.zip (modified) ( previous)
• src/perllib/plugins/OpenOfficeConverter.pm (modified) (1 diff)

gs2-extensions/open-office/trunk/src/perllib/plugins/OpenOfficeConverter.pm

@@ -100 +100 @@
         $status = system("which soffice >nul 2>&1"); # which.exe should be in bin/windows
         if ($status == 0) {
-            $cmd = "start \"soffice process\" $cmd >nul 2>&1"; # order of >nul and 2>&1 matters, see below
+            #$cmd = "start \"soffice process\" $cmd >nul 2>&1"; # order of >nul and 2>&1 matters, see below
+            
+            # On Windows, when perl/C/C++ uses system() to launch any standalone process in the background
+            # with "start \"window title\" cmd", perl's child process (despite being mostly independent/detached 
+            # from perl) *appears* to share stdout/stderr (stdin) streams with the parent perl process. This is
+            # noticeable with perl launching soffice or any program that neither writes to stderr/out nor sends
+            # eof/eos to indicate parent perl's streams are closed (e.g. Notepad).
+            # This is *not* a problem when perl scripts are run from command line. Command line programs run fine.
+            # But when combined with SafeProcess used by GLI, such silent standalone programs like soffice
+            # cause GLI to hang every time right until the silent program's terminated, because SafeProcess' join()
+            # calls on the perl child process' stderr and stdout block at SafeProcess.InputStreamGobbler.readLine(),
+            # because these stderr/out streams didn't receive eof/eos, implying the silent grandchild process
+            # somehow kept them open.
+            # This is true at Windows/C's system() command level: InputStreamGobblers using join() calls (as SafeProcess
+            # does), combined with a c++ program that uses system() that launches something like Notepad, just all block
+            # until Notepad is closed.
+            # When perl calls a custom java BackgroundLauncher.java program to launch an external program with Runtime.exec(),
+            # this hanging problem doesn't happen as java's exec() is not implemented with Windows C's system().
+            # Similarly, a WScript file (vbs or js script) that uses WinScriptHost.Run method to run an external program
+            # also doesn't exhibit this problem. So we use a custom vbs script to launch external programs like soffice in
+            # the background from perl (to avoid having to set up Java or have the java program compiled up by the release-kits,
+            # since perl building scripts are not just run from GLI but are also run directly from the cmd line).
+            
+            $cmd = "CScript //Nologo $ENV{'GSDLHOME'}\\bin\\windows\\background-launcher.vbs $cmd"; 
+            
             #print STDERR "***** Tried to start-up OpenOffice with:\n$cmd\n";           
         }