Annuaire d'articles
1. Origines
Le journal de l'environnement de production s'est soudainement étendu à 100 G+. Afin de localiser le problème, certains journaux d'erreurs ont été interceptés.
Le problème vient des informations sur la pile ? Où le NPE est-il signalé ? ? a>
Message comme suit :
[ERROR] 2020-12-09 09:41:50.053 - [taskAppId=TASK-1919-33805-97659]:[156] - wait task quit failed, instance id:33805, task id:97659
[ERROR] 2020-12-09 09:41:50.053 - [taskAppId=TASK-1919-34759-100696]:[154] - exception
java.lang.NullPointerException: null
[ERROR] 2020-12-09 09:41:50.053 - [taskAppId=TASK-1919-34759-100696]:[156] - wait task quit failed, instance id:34759, task id:100696
[ERROR] 2020-12-09 09:41:50.059 - [taskAppId=TASK-1917-7841-18206]:[154] - exception
java.lang.NullPointerException: null
[ERROR] 2020-12-09 09:41:50.059 - [taskAppId=TASK-1917-7841-18206]:[156] - wait task quit failed, instance id:7841, task id:18206
[ERROR] 2020-12-09 09:41:50.059 - [taskAppId=TASK-1919-33805-97659]:[154] - exception
java.lang.NullPointerException: null
2. Raisons
Il existe un paramètre dans JVM :OmitStackTraceInFastThrow, qui omet les informations sur la pile d'exceptions pour lever rapidement des exceptions.
La JVM a optimisé Fast Throw pour certains types d'exceptions spécifiques. Si elle détecte que le même type d'exception est levé plusieurs fois à un certain emplacement du code, C2 décidera d'utiliser la méthode Fast Throw pour lever l'exception, et le exception Trace est l'exception détaillée. Les informations de la pile seront effacées. Ce type d'exception est généré très rapidement car il n'est pas nécessaire d'allouer de la mémoire dans le tas ou de construire des informations complètes sur la pile d'exceptions.
Si désactivé, utilisez la commande suivante :
-XX:-OmitStackTraceInFastThrow
Code source de la JVM :
//------------------------------builtin_throw----------------------------------
void GraphKit::builtin_throw(Deoptimization::DeoptReason reason, Node* arg) {
bool must_throw = true;
if (env()->jvmti_can_post_on_exceptions()) {
// check if we must post exception events, take uncommon trap if so
uncommon_trap_if_should_post_on_exceptions(reason, must_throw);
// here if should_post_on_exceptions is false
// continue on with the normal codegen
}
//
// If this particular condition has not yet happened at this
// bytecode, then use the uncommon trap mechanism, and allow for
// a future recompilation if several traps occur here.
// If the throw is hot, try to use a more complicated inline mechanism
// which keeps execution inside the compiled code.
bool treat_throw_as_hot = false;
ciMethodData* md = method()->method_data();
if (ProfileTraps) {
if (too_many_traps(reason)) {
treat_throw_as_hot = true;
}
// (If there is no MDO at all, assume it is early in
// execution, and that any deopts are part of the
// startup transient, and don't need to be remembered.)
// Also, if there is a local exception handler, treat all throws
// as hot if there has been at least one in this method.
if (C->trap_count(reason) != 0
&& method()->method_data()->trap_count(reason) != 0
&& has_ex_handler()) {
treat_throw_as_hot = true;
}
}
// If this throw happens frequently, an uncommon trap might cause
// a performance pothole. If there is a local exception handler,
// and if this particular bytecode appears to be deoptimizing often,
// let us handle the throw inline, with a preconstructed instance.
// Note: If the deopt count has blown up, the uncommon trap
// runtime is going to flush this nmethod, not matter what.
if (treat_throw_as_hot
&& (!StackTraceInThrowable || OmitStackTraceInFastThrow)) {
// If the throw is local, we use a pre-existing instance and
// punt on the backtrace. This would lead to a missing backtrace
// (a repeat of 4292742) if the backtrace object is ever asked
// for its backtrace.
// Fixing this remaining case of 4292742 requires some flavor of
// escape analysis. Leave that for the future.
ciInstance* ex_obj = NULL;
switch (reason) {
case Deoptimization::Reason_null_check:
ex_obj = env()->NullPointerException_instance();
break;
case Deoptimization::Reason_div0_check:
ex_obj = env()->ArithmeticException_instance();
break;
case Deoptimization::Reason_range_check:
ex_obj = env()->ArrayIndexOutOfBoundsException_instance();
break;
case Deoptimization::Reason_class_check:
if (java_bc() == Bytecodes::_aastore) {
ex_obj = env()->ArrayStoreException_instance();
} else {
ex_obj = env()->ClassCastException_instance();
}
break;
}
if (failing()) {
stop(); return; } // exception allocation might fail
if (ex_obj != NULL) {
// Cheat with a preallocated exception object.
if (C->log() != NULL)
C->log()->elem("hot_throw preallocated='1' reason='%s'",
Deoptimization::trap_reason_name(reason));
const TypeInstPtr* ex_con = TypeInstPtr::make(ex_obj);
Node* ex_node = _gvn.transform( ConNode::make(C, ex_con) );
// Clear the detail message of the preallocated exception object.
// Weblogic sometimes mutates the detail message of exceptions
// using reflection.
int offset = java_lang_Throwable::get_detailMessage_offset();
const TypePtr* adr_typ = ex_con->add_offset(offset);
Node *adr = basic_plus_adr(ex_node, ex_node, offset);
const TypeOopPtr* val_type = TypeOopPtr::make_from_klass(env()->String_klass());
// Conservatively release stores of object references.
Node *store = store_oop_to_object(control(), ex_node, adr, adr_typ, null(), val_type, T_OBJECT, MemNode::release);
add_exception_state(make_exception_state(ex_node));
return;
}
}
// %%% Maybe add entry to OptoRuntime which directly throws the exc.?
// It won't be much cheaper than bailing to the interp., since we'll
// have to pass up all the debug-info, and the runtime will have to
// create the stack trace.
// Usual case: Bail to interpreter.
// Reserve the right to recompile if we haven't seen anything yet.
assert(!Deoptimization::reason_is_speculate(reason), "unsupported");
Deoptimization::DeoptAction action = Deoptimization::Action_maybe_recompile;
if (treat_throw_as_hot
&& (method()->method_data()->trap_recompiled_at(bci(), NULL)
|| C->too_many_traps(reason))) {
// We cannot afford to take more traps here. Suffer in the interpreter.
if (C->log() != NULL)
C->log()->elem("hot_throw preallocated='0' reason='%s' mcount='%d'",
Deoptimization::trap_reason_name(reason),
C->trap_count(reason));
action = Deoptimization::Action_none;
}
// "must_throw" prunes the JVM state to include only the stack, if there
// are no local exception handlers. This should cut down on register
// allocation time and code size, by drastically reducing the number
// of in-edges on the call to the uncommon trap.
uncommon_trap(reason, action, (ciKlass*)NULL, (char*)NULL, must_throw);
}
3. Vérification des codes
Code d'essai :
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
public class OmitStackTraceInFastThrowTest {
public static void main(String[] args) throws InterruptedException {
NPEThread npeThread = new NPEThread();
ExecutorService executorService = Executors.newFixedThreadPool(20);
for (int i=0; i<Integer.MAX_VALUE; i++) {
executorService.execute(npeThread);
// 稍微sleep一下, 是为了不要让异常抛出太快, 导致控制台输出太快, 把有异常栈信息冲掉, 只留下fast throw方式抛出的异常
Thread.sleep(2);
}
}
}
class NPEThread extends Thread {
private static int count = 0;
@Override
public void run() {
try{
System.out.println(this.getClass().getSimpleName()+"--"+(++count));
String str = null;
// 制造空指针NPE
System.out.println(str.length());
}catch (Throwable e){
e.printStackTrace();
}
}
}
Après une longue exécution, les informations de la pile ne sont plus imprimées. Le journal est le suivant :
NPEThread--467
NPEThread--468
NPEThread--469
NPEThread--470
NPEThread--471
NPEThread--472
NPEThread--473
NPEThread--474
NPEThread--475
NPEThread--476
NPEThread--477
java.lang.NullPointerException
at org.apache.dolphinscheduler.api.utils.NPEThread.run(OmitStackTraceInFastThrowTest.java:28)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at java.lang.Thread.run(Thread.java:748)
java.lang.NullPointerException
at org.apache.dolphinscheduler.api.utils.NPEThread.run(OmitStackTraceInFastThrowTest.java:28)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at java.lang.Thread.run(Thread.java:748)
java.lang.NullPointerException
at org.apache.dolphinscheduler.api.utils.NPEThread.run(OmitStackTraceInFastThrowTest.java:28)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at java.lang.Thread.run(Thread.java:748)
java.lang.NullPointerException
at org.apache.dolphinscheduler.api.utils.NPEThread.run(OmitStackTraceInFastThrowTest.java:28)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at java.lang.Thread.run(Thread.java:748)
java.lang.NullPointerException
at org.apache.dolphinscheduler.api.utils.NPEThread.run(OmitStackTraceInFastThrowTest.java:28)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at java.lang.Thread.run(Thread.java:748)
java.lang.NullPointerException
at org.apache.dolphinscheduler.api.utils.NPEThread.run(OmitStackTraceInFastThrowTest.java:28)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at java.lang.Thread.run(Thread.java:748)
java.lang.NullPointerException
at org.apache.dolphinscheduler.api.utils.NPEThread.run(OmitStackTraceInFastThrowTest.java:28)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at java.lang.Thread.run(Thread.java:748)
java.lang.NullPointerException
at org.apache.dolphinscheduler.api.utils.NPEThread.run(OmitStackTraceInFastThrowTest.java:28)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at java.lang.Thread.run(Thread.java:748)
java.lang.NullPointerException
at org.apache.dolphinscheduler.api.utils.NPEThread.run(OmitStackTraceInFastThrowTest.java:28)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at java.lang.Thread.run(Thread.java:748)
java.lang.NullPointerException
at org.apache.dolphinscheduler.api.utils.NPEThread.run(OmitStackTraceInFastThrowTest.java:28)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at java.lang.Thread.run(Thread.java:748)
java.lang.NullPointerException
at org.apache.dolphinscheduler.api.utils.NPEThread.run(OmitStackTraceInFastThrowTest.java:28)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at java.lang.Thread.run(Thread.java:748)
java.lang.NullPointerException
at org.apache.dolphinscheduler.api.utils.NPEThread.run(OmitStackTraceInFastThrowTest.java:28)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at java.lang.Thread.run(Thread.java:748)
java.lang.NullPointerException
at org.apache.dolphinscheduler.api.utils.NPEThread.run(OmitStackTraceInFastThrowTest.java:28)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at java.lang.Thread.run(Thread.java:748)
Après une longue exécution, les informations de la pile ne sont plus imprimées. Le journal est le suivant :
NPEThread--9030
NPEThread--9031
NPEThread--9032
NPEThread--9033
NPEThread--9034
NPEThread--9035
NPEThread--9036
NPEThread--9037
NPEThread--9038
NPEThread--9039
NPEThread--9040
NPEThread--9041
java.lang.NullPointerException
java.lang.NullPointerException
java.lang.NullPointerException
java.lang.NullPointerException
java.lang.NullPointerException
java.lang.NullPointerException
java.lang.NullPointerException
java.lang.NullPointerException
java.lang.NullPointerException
java.lang.NullPointerException
java.lang.NullPointerException
java.lang.NullPointerException
java.lang.NullPointerException