HPCC-9611 Can't run more than one thor job that uses Java

The libjavaembed plugin does not operate correctly if loaded and unloaded
(this is due to JVM limitations).

This does not cause issues for Roxie or hThor, but thor loads referenced
plugins per job, and will thus fail the second time a job references java.

Rather than refactor the (obsolete) plugin mechanism to allow indication of
'keep loaded' status, add code into the plugin itself to 'leak' a reference in
order to prevent it from unloading after having been loaded for the first
time.

Signed-off-by: Richard Chapman <rchapman@hpccsystems.com>

plugins/javaembed/javaembed.cpp

@@ -65,7 +65,7 @@ namespace javaembed {
 //    likes to set its own (in particular, it seems to intercept and ignore some SIGSEGV during the
 //    garbage collection).
 // Unfortunately, it seems that the design of the JNI interface is such that JNI_CreateJavaVM has to be called on the 'main thread'.
-// So we can't achieve 1, and 2 requires that we create via the INIT_MODLE mechanism (rather than just a static object), and that
+// So we can't achieve 1, and 2 requires that we create via the INIT_MODULE mechanism (rather than just a static object), and that
 // any engines that call InitModuleObjects() or load plugins dynamically do so AFTER setting any signal handlers or calling
 // EnableSEHtoExceptionMapping
 //
@@ -115,15 +115,56 @@ public:
     JavaVM *javaVM;       /* denotes a Java VM */
 } *globalState;
 
+#ifdef _WIN32
+    EXTERN_C IMAGE_DOS_HEADER __ImageBase;
+#endif
+
 MODULE_INIT(INIT_PRIORITY_STANDARD)
 {
     globalState = new JavaGlobalState;
+    // Make sure we are never unloaded (as JVM does not support it)
+    // we do this by doing a dynamic load of the javaembed library
+#ifdef _WIN32
+    char path[_MAX_PATH];
+    ::GetModuleFileName((HINSTANCE)&__ImageBase, path, _MAX_PATH);
+    if (strstr(path, "javaembed"))
+    {
+        HINSTANCE h = LoadSharedObject(path, false, false);
+        DBGLOG("LoadSharedObject returned %p", h);
+    }
+#else
+    FILE *diskfp = fopen("/proc/self/maps", "r");
+    if (diskfp)
+    {
+        char ln[_MAX_PATH];
+        while (fgets(ln, sizeof(ln), diskfp))
+        {
+            if (strstr(ln, "libjavaembed"))
+            {
+                const char *fullName = strchr(ln, '/');
+                if (fullName)
+                {
+                    char *tail = (char *) strstr(fullName, SharedObjectExtension);
+                    if (tail)
+                    {
+                        tail[strlen(SharedObjectExtension)] = 0;
+                        HINSTANCE h = LoadSharedObject(fullName, false, false);
+                        DBGLOG("LoadSharedObject %s returned %p", fullName, h);
+                        break;
+                    }
+                }
+            }
+        }
+        fclose(diskfp);
+    }
+#endif
     return true;
 }
 MODULE_EXIT()
 {
-    delete globalState;
-    globalState = NULL;
+    // We don't attempt to destroy the Java VM, as it's buggy...
+//    delete globalState;
+//    globalState = NULL;
 }
 
 static void checkType(type_t javatype, size32_t javasize, type_t ecltype, size32_t eclsize)