Bug 569853 - jstack crashes Eclipse when running on Java 11

1) Always call DetachCurrentThread if AttachCurrentThreadAsDaemon was
called before, see
https://docs.oracle.com/javase/8/docs/technotes/guides/jni/spec/invocation.html#detaching_from_the_vm.

2) Specify JNI 1.4 version in JNI_OnLoad, see
https://docs.oracle.com/en/java/javase/11/docs/specs/jni/invocation.html#jni_onload

3) Added printf around attach/detach for easier debugging.

4) Fixed build.sh to allow c99 standard for the for loop defined in
DEBUG_CALL_PRINTS and resolve compilation error below if
DEBUG_CALL_PRINTS is enabled:

callback.c:1252:3: error: 'for' loop initial declarations are only
allowed in C99 mode

Main change is 1), it is a workaround for jstack / JVM bug described in
https://bugzilla.redhat.com/show_bug.cgi?id=1897150

Change-Id: I3ba32d9bef217e5ffc76b8802e7e59de503a2161

4 files changed, 13 insertions, 24 deletions

diff --git a/bundles/org.eclipse.swt/Eclipse SWT PI/gtk/library/build.sh b/bundles/org.eclipse.swt/Eclipse SWT PI/gtk/library/build.sh
index 0490465334..61f01449a3 100755
--- a/bundles/org.eclipse.swt/Eclipse SWT PI/gtk/library/build.sh
+++ b/bundles/org.eclipse.swt/Eclipse SWT PI/gtk/library/build.sh
@@ -116,7 +116,7 @@ esac
 case $SWT_OS.$SWT_ARCH in
 	"linux.x86_64")
 		if [ "${CC}" = "" ]; then
-			export CC=gcc
+			export CC="gcc -std=c99"
 		fi
 		if [ "${JAVA_HOME}" = "" ]; then
 			# Cross-platform method of finding JAVA_HOME.
diff --git a/bundles/org.eclipse.swt/Eclipse SWT/common/library/callback.c b/bundles/org.eclipse.swt/Eclipse SWT/common/library/callback.c
index 1e37e28810..0bd7b87a77 100644
--- a/bundles/org.eclipse.swt/Eclipse SWT/common/library/callback.c
+++ b/bundles/org.eclipse.swt/Eclipse SWT/common/library/callback.c
@@ -1298,24 +1298,15 @@ jlong callback(int index, ...)
 	}
 #endif
 
-#ifdef JNI_VERSION_1_2
-	if (IS_JNI_1_2) {
-		(*JVM)->GetEnv(JVM, (void **)&env, JNI_VERSION_1_2);
-	}
-#endif
-	
-#ifdef JNI_VERSION_1_4
-	if (env == NULL) {
-		if (JNI_VERSION >= JNI_VERSION_1_4) {
-			(*JVM)->AttachCurrentThreadAsDaemon(JVM, (void **)&env, NULL);
-		}
-	}
+(*JVM)->GetEnv(JVM, (void **)&env, JNI_VERSION_1_4);
+
+if (env == NULL) {
+	(*JVM)->AttachCurrentThreadAsDaemon(JVM, (void **)&env, NULL);
+#ifdef DEBUG_CALL_PRINTS
+	fprintf(stderr, "SWT-JNI: AttachCurrentThreadAsDaemon\n");
 #endif
-	
-	if (env == NULL) {
-		(*JVM)->AttachCurrentThread(JVM, (void **)&env, NULL);
-		if (IS_JNI_1_2) detach = 1;
-	}
+	detach = 1;
+}
 	
 	/* If the current thread is not attached to the VM, it is not possible to call into the VM */
 	if (env == NULL) {
@@ -1391,6 +1382,9 @@ done:
 
 	if (detach) {
 		(*JVM)->DetachCurrentThread(JVM);
+#ifdef DEBUG_CALL_PRINTS
+		fprintf(stderr, "SWT-JNI: DetachCurrentThread\n");
+#endif
 		env = NULL;
 	}
 
diff --git a/bundles/org.eclipse.swt/Eclipse SWT/common/library/swt.c b/bundles/org.eclipse.swt/Eclipse SWT/common/library/swt.c
index e78a2e4811..483aae2d47 100644
--- a/bundles/org.eclipse.swt/Eclipse SWT/common/library/swt.c
+++ b/bundles/org.eclipse.swt/Eclipse SWT/common/library/swt.c
@@ -14,16 +14,12 @@
  
 #include "swt.h"
 
-int IS_JNI_1_2 = 0;
 JavaVM *JVM = NULL;
 
-#ifdef JNI_VERSION_1_2
 JNIEXPORT jint JNICALL JNI_OnLoad(JavaVM *vm, void *reserved) {
-	IS_JNI_1_2 = 1;
 	JVM = vm;
-	return JNI_VERSION_1_2;
+	return JNI_VERSION_1_4;
 }
-#endif
 
 void throwOutOfMemory(JNIEnv *env) {
 	jclass clazz = (*env)->FindClass(env, "java/lang/OutOfMemoryError");
diff --git a/bundles/org.eclipse.swt/Eclipse SWT/common/library/swt.h b/bundles/org.eclipse.swt/Eclipse SWT/common/library/swt.h
index fa228e9971..32f39f01bd 100644
--- a/bundles/org.eclipse.swt/Eclipse SWT/common/library/swt.h
+++ b/bundles/org.eclipse.swt/Eclipse SWT/common/library/swt.h
@@ -29,7 +29,6 @@
 extern "C" {
 #endif
 
-extern int IS_JNI_1_2;
 extern JavaVM *JVM;
 
 /* #define DEBUG */