tdf#95843: Wait for fire_glxtest_process also in --headless mode

Discussed with mmeeks on IRC that fire_glxtest_process is probably called as
early as possible so that its reuslt is ready by the time it is needed in the
non-headless case.  So best fix for headless is probably to just wait for the
sub-process at an opportune point, instead of redesigning the whole mess so that
fire_glxtest_process would only be called once its result is actually needed.

Change-Id: I4ea9c9d54b83c9695a3b72317e68fed0c410da0e
Reviewed-on: https://gerrit.libreoffice.org/53154Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>

desktop/inc/app.hxx

@@ -183,6 +183,7 @@ OUString ReplaceStringHookProc(const OUString& rStr);
 
 #if defined( UNX ) && !defined MACOSX && !defined IOS && !defined ANDROID && !defined LIBO_HEADLESS
 bool fire_glxtest_process();
+void reap_glxtest_process();
 #endif
 
 #endif // INCLUDED_DESKTOP_INC_APP_HXX

desktop/source/app/app.cxx

@@ -1587,6 +1587,15 @@ int Desktop::Main()
         CheckOpenCLCompute(xDesktop);
 #endif
 
+        // In headless mode, reap the process started by fire_glxtest_process() early in soffice_main
+        // (desktop/source/app/sofficemain.cxx), in a code block that needs to be covered by the same
+        // #if condition as this code block:
+#if defined( UNX ) && !defined MACOSX && !defined IOS && !defined ANDROID && !defined(LIBO_HEADLESS) && HAVE_FEATURE_OPENGL
+        if (rCmdLineArgs.IsHeadless()) {
+            reap_glxtest_process();
+        }
+#endif
+
         // Release solar mutex just before we wait for our client to connect
         {
             SolarMutexReleaser aReleaser;

desktop/source/app/sofficemain.cxx

@@ -125,6 +125,10 @@ extern "C" int DESKTOP_DLLPUBLIC soffice_main()
 #if defined( UNX ) && !defined MACOSX && !defined IOS && !defined ANDROID && !defined(LIBO_HEADLESS) && HAVE_FEATURE_OPENGL
     /* Run test for OpenGL support in own process to avoid crash with broken
      * OpenGL drivers. Start process as early as possible.
+     * In non-headless mode, the process will be reaped in X11OpenGLDeviceInfo::GetData
+     * (vcl/opengl/x11/X11DeviceInfo.cxx).  In headless mode, the process will be reaped late in
+     * Desktop::Main (desktop/source/app/app.cxx), in a code block that needs to be covered by the
+     * same #if condition as this code block.
      */
     bool bSuccess = fire_glxtest_process();
     SAL_WARN_IF(!bSuccess, "desktop.opengl", "problems with glxtest");

vcl/inc/opengl/x11/glxtest.hxx

@@ -18,6 +18,8 @@ VCL_DLLPUBLIC pid_t* getGlxPid();
 
 bool fire_glxtest_process();
 
+void reap_glxtest_process();
+
 #endif
 
 /* vim:set shiftwidth=4 softtabstop=4 expandtab: */

vcl/unx/glxtest.cxx

@@ -27,6 +27,8 @@
 #include <string.h>
 #include <signal.h>
 
+#include <sys/wait.h>
+
 #include <opengl/x11/glxtest.hxx>
 
 #ifdef __SUNPRO_CC
@@ -36,6 +38,8 @@
 #include <X11/Xlib.h>
 #include <X11/Xutil.h>
 
+#include <sal/log.hxx>
+
 // stuff from glx.h
 typedef struct __GLXcontextRec *GLXContext;
 typedef XID GLXPixmap;
@@ -275,3 +279,15 @@ bool fire_glxtest_process()
   *glxtest_pid = pid;
   return true;
 }
+
+void reap_glxtest_process() {
+    pid_t * pid = getGlxPid();
+    if (*pid != 0) {
+        // Use WNOHANG, as it is probably better to have a (rather harmless) zombie child process
+        // hanging around for the duration of the calling process, than to potentially block the
+        // calling process here:
+        pid_t e = waitpid(*pid, nullptr, WNOHANG);
+        SAL_INFO_IF(
+            e <= 0, "vcl.opengl", "waiting for glxtest process " << *pid << " failed with " << e);
+    }
+}