Java – why does JIT compile some methods at startup?
•
Java
I am studying JIT behavior on a very simple code block:
public class PlayWithAssembly {
public static void main(String[] args) {
Random random = new Random();
random.nextInt();
}
}
In fact, as far as my question is concerned, the content of the main method is completely irrelevant I'm running Ubuntu 16.04 Openjdk 10.0 is used on 5 1 and run the following code with the following command Java - xbatch - XX: printcompilation - XX: compilethreshold = 1000000 - CP target / classes com xxx. playground. internal. bytecode. PlayWithAssembly
Since compilethreshold is set to a very high value, I don't want to JIT compile anything. I'd rather expect the JVM to run completely in interpretation mode in the practice of this example But when I run the above command, I get a list of compiled methods (all of which are part of the JDK):
47 1 b 3 java.lang.Stringlatin1::hashCode (42 bytes) 50 2 b 3 java.util.concurrent.ConcurrentHashMap::tabAt (22 bytes) 51 3 n 0 jdk.internal.misc.Unsafe::getObjectVolatile (native) 55 4 b 3 java.lang.Object::<init> (1 bytes) 56 5 b 3 java.lang.String::islatin1 (19 bytes) 56 6 b 3 java.lang.String::hashCode (49 bytes) 57 7 b 3 java.lang.String::coder (15 bytes) 58 8 b 3 java.lang.Math::floorMod (10 bytes) 59 9 b 3 java.util.ImmutableCollections$SetN::probe (60 bytes) 62 10 b 1 java.util.ImmutableCollections$Set0::hashCode (2 bytes) 62 11 b 3 java.lang.String::equals (65 bytes) 64 12 b 1 java.util.Collections$EmptySet::hashCode (2 bytes) 65 13 b 3 java.lang.Stringlatin1::equals (36 bytes) 66 14 b 3 java.util.Collections::emptySet (4 bytes) 66 15 b 3 java.lang.module.ModuleDescriptor$Exports::<init> (10 bytes) 67 16 b 4 java.lang.Stringlatin1::hashCode (42 bytes) 71 1 3 java.lang.Stringlatin1::hashCode (42 bytes) made not entrant 72 17 b 3 java.lang.module.ModuleDescriptor$Exports::hashCode (38 bytes) 73 18 b 3 java.util.Objects::equals (23 bytes) 73 19 b 3 java.util.Objects::requireNonNull (14 bytes) 74 20 b 3 java.util.AbstractCollection::<init> (5 bytes) 76 21 b 3 java.util.AbstractSet::<init> (5 bytes) 76 22 b 3 java.util.ImmutableCollections$AbstractImmutableSet::<init> (5 bytes) 77 23 b 1 java.lang.Object::<init> (1 bytes) 77 4 3 java.lang.Object::<init> (1 bytes) made not entrant 81 24 b 1 java.lang.module.ModuleDescriptor::name (5 bytes) 82 25 b 1 java.lang.module.ModuleReference::descriptor (5 bytes) 88 26 b 3 java.lang.String::charAt (25 bytes) 93 27 b 3 java.util.concurrent.ConcurrentHashMap::spread (10 bytes) 94 28 b 3 java.util.ImmutableCollections$SetN$1::hasNext (47 bytes) 95 29 b 3 java.util.ImmutableCollections$SetN$1::next (35 bytes) 96 30 b 3 java.util.Set::of (66 bytes) 98 31 b 1 java.util.KeyValueHolder::getKey (5 bytes) 99 32 b 1 java.util.KeyValueHolder::getValue (5 bytes) 100 33 b 3 java.util.ImmutableCollections$MapN::probe (64 bytes) 101 34 b 3 java.util.KeyValueHolder::<init> (21 bytes) 102 35 b 3 java.util.ImmutableCollections$MapN::get (21 bytes) 103 36 n 0 java.lang.Object::hashCode (native) 103 37 b 3 jdk.internal.module.ModuleReferenceImpl::hashCode (56 bytes) 105 38 b 3 java.util.HashMap::hash (20 bytes) 106 39 !b 3 java.util.concurrent.ConcurrentHashMap::putVal (432 bytes) 112 40 n 0 jdk.internal.misc.Unsafe::compareAndSetLong (native) 112 41 b 3 java.util.concurrent.ConcurrentHashMap::putIfAbsent (8 bytes) 112 42 b 1 java.lang.module.ResolvedModule::reference (5 bytes) 113 43 b 3 java.util.concurrent.ConcurrentHashMap::addCount (289 bytes) 115 2 3 java.util.concurrent.ConcurrentHashMap::tabAt (22 bytes) made not entrant 115 39 ! 3 java.util.concurrent.ConcurrentHashMap::putVal (432 bytes) made not entrant 115 44 b 3 jdk.internal.misc.Unsafe::getObjectAcquire (7 bytes) 116 45 b 3 java.util.concurrent.ConcurrentHashMap::tabAt (22 bytes) 116 46 n 0 jdk.internal.misc.Unsafe::compareAndSetObject (native) 117 47 b 3 java.util.concurrent.ConcurrentHashMap$Node::<init> (20 bytes) 117 48 !b 3 java.util.concurrent.ConcurrentHashMap::putVal (432 bytes) 120 49 b 3 java.util.concurrent.ConcurrentHashMap::casTabAt (21 bytes) 122 50 b 3 java.util.HashMap::getNode (148 bytes) 124 51 b 3 java.lang.String::length (11 bytes) 125 52 b 3 java.lang.Stringlatin1::canEncode (13 bytes) 126 53 b 3 java.util.HashMap::put (13 bytes) 127 54 n 0 java.lang.System::arraycopy (native) (static) 128 55 b 3 java.util.HashMap$Node::<init> (26 bytes) 128 56 b 3 java.util.HashMap::newNode (13 bytes) 129 57 b 3 java.util.HashMap::afterNodeInsertion (1 bytes) 129 58 b 3 java.util.Optional::ofNullable (15 bytes) 131 59 b 3 java.util.HashMap::get (23 bytes) 132 60 b 3 java.util.HashMap::putVal (300 bytes) 135 61 b 1 java.lang.module.ModuleDescriptor$Exports::source (5 bytes) 135 62 b 1 java.util.Collections$1::hasNext (5 bytes) 136 63 b 3 java.lang.module.ResolvedModule::name (11 bytes) 137 64 b 3 java.util.HashSet::add (20 bytes) 137 65 b 1 java.util.Collections$EmptySet::isEmpty (2 bytes) 138 66 b 3 java.lang.module.ResolvedModule::hashCode (16 bytes) 139 67 b 3 java.lang.module.ModuleDescriptor$Exports::isQualified (18 bytes) 140 68 b 1 java.lang.module.ModuleDescriptor::isAutomatic (5 bytes) 140 69 b 3 java.util.AbstractMap::<init> (5 bytes) 141 70 b 1 java.lang.module.ModuleDescriptor$Exports::targets (5 bytes) 141 71 b 1 java.lang.module.ResolvedModule::configuration (5 bytes) 142 72 b 3 java.util.HashMap::<init> (11 bytes) 142 73 b 3 java.util.ImmutableCollections$Set2$1::hasNext (14 bytes) 143 74 b 4 java.util.ImmutableCollections$SetN$1::hasNext (47 bytes) 148 28 3 java.util.ImmutableCollections$SetN$1::hasNext (47 bytes) made not entrant 149 75 b 1 java.util.ImmutableCollections$Set1::size (2 bytes) 150 76 b 3 java.lang.Math::min (11 bytes) 152 77 b 3 java.util.AbstractCollection::isEmpty (13 bytes) 153 78 b 4 java.lang.String::hashCode (49 bytes) 160 6 3 java.lang.String::hashCode (49 bytes) made not entrant 162 79 b 3 java.util.Map::entry (10 bytes) 165 80 b 1 java.lang.module.ModuleDescriptor::isOpen (5 bytes) 167 81 b 1 java.util.HashMap::afterNodeInsertion (1 bytes) 167 57 3 java.util.HashMap::afterNodeInsertion (1 bytes) made not entrant 168 82 b 3 jdk.internal.module.ModuleBootstrap$2::hasNext (30 bytes) 169 83 b 3 java.util.HashMap::resize (356 bytes) 171 84 b 3 java.util.Collections$UnmodifiableCollection$1::hasNext (10 bytes) 172 85 b 3 jdk.internal.module.ModuleBootstrap$2::next (52 bytes) 173 86 b 3 java.util.HashMap::putIfAbsent (13 bytes) 174 87 n 0 java.lang.Module::addExportsToAllUnnamed0 (native) (static) 175 88 b 1 java.lang.Module::getDescriptor (5 bytes) 182 78 4 java.lang.String::hashCode (49 bytes) made not entrant 185 89 b 3 java.lang.Stringlatin1::indexOf (61 bytes) 187 23 1 java.lang.Object::<init> (1 bytes) made not entrant 195 90 b 1 java.lang.Object::<init> (1 bytes) 197 91 b 3 java.lang.String::hashCode (49 bytes)
I try to match these methods to the list of intrinsic functions, but it doesn't match, so my question is: Why are these methods compiled (while other methods are not), do I have any control over it?
Solution
Starting from the document of - XX: compilethreshold:
Therefore, when - XX: - tieredcompilation is specified, most of these entries will disappear, but some entries can still be exempted from counter based compilation decisions
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