DB
Uploaded byDavid Buck
PDF, PPTX164 views

Java Concurrency, A(nother) Peek Under the Hood [Code One 2019]

The document outlines a product direction intended for information purposes only and is not binding. Any features or functionality described may change or be removed at Oracle's sole discretion. Statements relating to Oracle's plans are forward-looking and subject to risks. All information is current as of September 2019. Oracle undertakes no duty to update any statement in light of new information or future events. The document is intended to provide a non-binding overview of Oracle's general product direction and is not a commitment to deliver any functionality.

Embed presentation

Download as PDF, PPTX
1 / 113
2 / 113
3 / 113
4 / 113
5 / 113
6 / 113
7 / 113
8 / 113
9 / 113
10 / 113
11 / 113
12 / 113
13 / 113
14 / 113
15 / 113
16 / 113
17 / 113
18 / 113
19 / 113
20 / 113
21 / 113
22 / 113
23 / 113
24 / 113
25 / 113
26 / 113
27 / 113
28 / 113
29 / 113
30 / 113
31 / 113
32 / 113
33 / 113
34 / 113
35 / 113
36 / 113
37 / 113
38 / 113
39 / 113
40 / 113
41 / 113
42 / 113
43 / 113
44 / 113
45 / 113
46 / 113
47 / 113
48 / 113
49 / 113
50 / 113
51 / 113
52 / 113
53 / 113
54 / 113
55 / 113
56 / 113
57 / 113
58 / 113
59 / 113
60 / 113
61 / 113
62 / 113
63 / 113
64 / 113
65 / 113
66 / 113
67 / 113
68 / 113
69 / 113
70 / 113
71 / 113
72 / 113
73 / 113
74 / 113
75 / 113
76 / 113
77 / 113
78 / 113
79 / 113
80 / 113
81 / 113
82 / 113
83 / 113
84 / 113
85 / 113
86 / 113
87 / 113
88 / 113
89 / 113
90 / 113
91 / 113
92 / 113
93 / 113
94 / 113
95 / 113
96 / 113
97 / 113
98 / 113
99 / 113
100 / 113
101 / 113
102 / 113
103 / 113
104 / 113
105 / 113
106 / 113
107 / 113
108 / 113
109 / 113
110 / 113
111 / 113
112 / 113
113 / 113
The following is intended to outline our general product direction. It is intended for information purposes only, and may not be incorporated into any contract. It is not a commitment to deliver any material, code, or functionality, and should not be relied upon in making purchasing decisions. The development, release, timing, and pricing of any features or functionality described for Oracle’s products may change and remains at the sole discretion of Oracle Corporation. Statements in this presentation relating to Oracle’s future plans, expectations, beliefs, intentions and prospects are “forward-looking statements” and are subject to material risks and uncertainties. A detailed discussion of these factors and other risks that affect our business is contained in Oracle’s Securities and Exchange Commission (SEC) filings, including our most recent reports on Form 10-K and Form 10-Q under the heading “Risk Factors.” These filings are available on the SEC’s website or on Oracle’s website at http://www.oracle.com/investor. All information in this presentation is current as of September 2019 and Oracle undertakes no duty to update any statement in light of new information or future events. Safe Harbor Copyright © 2019 Oracle and/or its affiliates.
Java Concurrency, A(nother) Peek Under the Hood [DEV4211] Principal Member of Technical Staff Java Platform Group September 19, 2019 David Buck Copyright © 2019 Oracle and/or its affiliates.
IoT Microservices DevOps in the Cloud Copyright © 2019 Oracle and/or its affiliates.
IoT Microservices DevOps in the Cloud Copyright © 2019 Oracle and/or its affiliates.
IoT Microservices DevOps in the Cloud Copyright © 2019 Oracle and/or its affiliates.
JVM Sustaining Engineer OpenJDK Update Project Maintainer JavaOne Rock Star Co-author of Oracle WebLogic Server 11g 構築・運用ガイド @DavidBuckJP https://blogs.oracle.com/buck/ Who am I? David Buck (left)
Program Agenda Introduction Background Tangent 1: Special Relativity History Implementation Tangent 2: HSDIS Future Conclusions 1 2 3 4 5 7 6
Introduction
Motivation “But I don’t write multithreaded code…”
Web Server picture: Coolcaesar at the English language Wikipedia [GFDL (http://www.gnu.org/copyleft/fdl.html) or CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0/)]
GUI
Libraries picture: David Vignoni / ICON KING (http://icon-king.com) [LGPL (http://www.gnu.org/licenses/lgpl.html) or LGPL (http://www.gnu.org/licenses/lgpl.html)]
Batch Processing picture: US Social Security Administration (http://www.ssa.gov/history/acalcs.html) [Public domain]
“But I don’t write multithreaded code…”
“But I don’t write multithreaded code…”
Race Conditions picture: Sakurambo at English Wikipedia [GFDL (http://www.gnu.org/copyleft/fdl.html) or CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0/)]
Heisenbugs Bug Heisenberg Heisenbug picture: Bundesarchiv, Bild 183-R57262 / Unknown / CC-BY-SA 3.0 [CC BY-SA 3.0 de (http://creativecommons.org/licenses/by-sa/3.0/de/deed.en)]
Observer Effect picture: Christian Schirm (Own work) [CC0]
Avoiding Heisenbugs Java Memory Model synchronized keyword java.util.concurrent
Avoiding Heisenbugs Java Memory Model synchronized keyword java.util.concurrent • Don’t do ＸＸＸ • You must do ＹＹＹ
a² + b² == c²
picture: WTF Public License, Version 2
Background
Memory Model
Memory Model Definition 1 Specification that explains when we can guarantee that a written value may be read correctly
void hogeMethod1() { int localA = 42; assert localA == 42; }
static int staticA; void hogeMethod2() { staticA = 42; assert staticA == 42; }
int data = 0; boolean ready = false; void hoge3() { while (!ready) {}; assert data == 42; } void hoge4() { data = 42; ready = true; }
Culprit #1
Culprit #2
Memory Ordering void hoge5() { a = 1; b = 2; c = 3; d = 4; e = 5; a = a + 1; }
Memory Ordering void hoge5() { a = 1; b = 2; c = 3; d = 4; e = 5; a = a + 1; } void hoge5() { a = 2; b = 2; c = 3; d = 4; e = 5; }
Memory Ordering void hoge5() { a = 1; b = 2; c = 3; d = 4; e = 5; a = a + 1; } void hoge5() { b = 2; c = 3; d = 4; e = 5; a = 2; }
Rule Single threaded behavior must never change
Out of Order Execution picture: Amit6, original version (File:Superscalarpipeline.png) by User:Poil (Own work) [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0)]
CPU Differences Type Alpha ARMv7 PA- RISC POWER SPARC RMO SPARC PSO SPARC TSO x86 x86 oostore AMD64 IA-64 zSeries load- load Y Y Y Y Y Y Y load- store Y Y Y Y Y Y Y store- store Y Y Y Y Y Y Y Y store- load Y Y Y Y Y Y Y Y Y Y Y Y Atomic (loads) Y Y Y Y Y Atomic (stores) Y Y Y Y Y Y Depend ent loads Y instruct ion cache Y Y Y Y Y Y Y Y Y Y chart source: https://en.wikipedia.org/wiki/Memory_ordering
CPU Differences Loose Strict Alpha X86
CPU Differences Loose Strict
Memory Barriers int data = 0; boolean ready = false; void hoge3() { while (!ready) {}; assert data == 42; } void hoge4() { data = 42; ready = true; }
Memory Barriers int data = 0; boolean ready = false; void hoge3() { while (!ready) {}; assert data == 42; } void hoge4() { data = 42; ready = true; }
Memory Barriers int data = 0; boolean ready = false; void hoge3() { while (!ready) {}; assert data == 42; } void hoge4() { data = 42; ready = true; }
Memory Barriers Types store-store store-load load-store load-load
Compiler Barriers GCC __asm__ __volatile__("":::"memory"); VC++ _ReadBarrier _WriteBarrier _ReadWriteBarrier
Tangent 1: Special Relativity picture: Sakurambo (Own work) [Public domain]
Tangent 1: Special Relativity A B C
Tangent 1: Special Relativity A B C A, B, C
Tangent 1: Special Relativity A B C A, B, C C, B, A
Tangent 1: Special Relativity Observed order depends on viewer's frame of reference A B C A, B, C C, B, A
No single “correct” timeline Special Relativity Observed order of events depends on frame of reference
No single “correct” timeline Special Relativity Observed order of events depends on frame of reference Multithreaded Code Observed order of events depends on thread
Memory Model Definition 2 Clarify what multithreaded behavior developers may depend on
Memory Model Definition 2 Clarify what multithreaded behavior developers may depend on Limits what types of optimizations the runtime may do
History
Java Memory Model (JMM) Write once, run anywhere 1995 Part of the formal language specification Happened-before picture: Peter Campbell [GFDL (http://www.gnu.org/copyleft/fdl.html) or CC BY-SA 4.0-3.0-2.5-2.0-1.0 (http://creativecommons.org/licenses/by-sa/4.0-3.0-2.5-2.0-1.0)]
happened-before
Leslie Lamport LaTex happened-before picture: Leslie Lamport [GFDL (http://en.wikipedia.org/wiki/GFDL]
happened-before void hoge5() { a = 1; b = 2; c = 3; d = 4; e = 5; a = a + 1; }
happened-before void hoge4() { data = 42; ready = true; } void hoge3() { while (!ready) {}; assert data == 42; }
happened-before void hoge4() { data = 42; ready = true; } void hoge3() { while (!ready) {}; assert data == 42; }
happened-before void synchronized hoge4() { data = 42; ready = true; } void synchronized hoge3() { while (!ready) {}; assert data == 42; } Warning: if hoge3 is executed first, the above code will deadlock
happened-before void synchronized hoge4() { data = 42; ready = true; } void synchronized hoge3() { while (!ready) {}; assert data == 42; } Warning: if hoge3 is executed first, the above code will deadlock
JMM Specification
Original JMM Keywords synchronized mutual exclusion happened-before
Original JMM Keywords synchronized mutual exclusion happened-before volatile Visibility
Problems with the Original JMM volatile does not establish a happened-before relationship final values can change Many important runtime optimization were not allowed
Doug Lea Author of the Java Multithreaded bible Introduced his own OSS high- level multithreaded library
Java SE 5.0 Modern JMM introduced Lea’s library added to official JDK picture: Zvi Roger [CC BY 3.0 (http://creativecommons.org/licenses/by/3.0)]
Modern JMM JSR-133 Fixed shortcomings in original JMM volatile does establish happens-before final values will never change
Modern JMM Keywords synchronized mutual exclusion happened-before volatile visibility happened-before final immutability
JSR-133 の volatile void hoge4() { data = 42; ready = true; } void hoge3() { while (!ready) {}; assert data == 42; } Warning: if hoge3 is executed first, the above code will deadlock volatile boolean ready = false;
volatile != atomic volatile int id = 0; int incID() { return id++; }
volatile != atomic volatile int id = 0; int incID() { return id++; } reg = [id] reg++ [id] = reg
volatile != atomic volatile int id = 0; synchronized int incID() { return id++; }
64-bit updates are not guaranteed atomic • Reads and Writes to long and double values may not happen atomically • Possible to read a mix of two different writes Copyright © 2019 Oracle and/or its affiliates. Old value MSB New value LSB
happened-before Monitor (acquisition / release) Volatile (read / write) final “freeze” (constructor) JNI System.out.println（） Input / Output thread start()/join() operations on j.u.concurrent collections
java.util.concurent JSR-166 Doug Lea’s OSS multithreading library
Multithreaded Control java.util.concurent synchronized wait()/notify() volatile / final Abstract Low-level
Fork/Join (JDK 7)
Functional Programming (JDK 8) Lambda Forms Stream API λ
Var Handles • Lower-level than volatile / final • Allows a value to be volatile only when we want it to be • Explicate fence and acquire / release semantics • Added in JDK 9 to replace several use cases previously only supported with sun.misc.Unsafe Copyright © 2019 Oracle and/or its affiliates.
Implementation
Tangent 2: HSDIS (HotSpot Disassembler) Lets us see code generated by JIT Requires a disassembler plugin GNU binutils-based plugin base-hsdis Command line options +PrintAssembly +CompileCommand=print,*MyClass.myMethod
Demos
ARM Assembly Crash Course
ARM Assembly Crash Course Op Target Source
ARM Assembly Crash Course MOV r02 #42
ARM Assembly Crash Course MOV r02 #42 r02 = 42
ARM Assembly Crash Course Op Target Source
ARM Assembly Crash Course Op Target Source Exception STR Source Target
ARM Assembly Crash Course MOV Copies registers MOV r02 r03 Writes Literals MOV r02 #42
ARM Assembly Crash Course LDx Loads data from memory to a register ldr r03, [r06] r03 = *r06
ARM Assembly Crash Course CMP / BEQ Compare and branch if equal cmp r0, #0 beq 0x74178d08 if (r0 == 0) goto 0x74178d08
ARM Assembly Crash Course DMB Data Memory Barrier dmb st dmb sy
One more thing…
Safe Points Methods proactively poll JVM makes page unreadable to stop the world movw ip, #45056 ; 0xb000 movt ip, #30461 ; 0x76fd ldr ip, [ip] ; {poll_return}
Long Value static long val = 0; public static void main(String[] args) { new Thread(() -> { while(true) val = -1L; } ).start(); new Thread(() -> { while(true) val = 0L; } ).start(); while (true) { long temp = val; if ( temp != -1 && temp != 0 ) { System.out.println("temp (DEC): " + temp); System.out.println("temp (BIN): " + Long.toBinaryString(temp)); System.exit(-1); } } }
Object Initialization public class ObjInit { static ObjInit globalRef = new ObjInit(); long number; public ObjInit() { number = 42; }
Object Initialization public static void main(String[] args) { new Thread(() -> { while(true) { long temp = globalRef.number; if (temp != 42) { System.out.println(temp); System.exit(-1); } } } ).start(); new Thread(() -> { while(true) globalRef = new ObjInit(); } ).start(); }}
public class Loop extends Thread { static boolean done = false; public static void main(String[] args) { Thread childThread = new Loop(); childThread.start(); System.out.println("Starting loop"); spinWait(); System.out.println("Exited loop"); } private static void spinWait() { while (!done) ; } public void run() { try { Thread.sleep(5 * 1000); } catch (Exception e) {} done = true; } } // class Loop Loop
Future
JEP-188/JMM9 Not delivered with JDK 9 (JMM9 != JDK 9) JVM-level specification Compatibility with C11/C++11 Cover new features added since JDK 5 (e.g. AtomicX.weakCompareAndSet())
Conclusions
Avoid low-level API java.util.concurent synchronized wait()/notify() volatile / final Var handles Abstract Low-level
Code against the specification Intermittent bugs are common Behavior changes with JRE / platform Stuff to avoid synchronized (new Object()) { } Randomly adding volatile declarations until it magically starts working
Testing As close to production environment as possible Same hardware Same JRE (including version） Same settings
Testing As much variety as possible Various hardware Various JREs (including version） Various settings
Java Concurrency in Practice Java Concurrency Bible Covers JSR-133 / JSR-166
Summary Avoid low-level APIs Code against the standard, not the implementation Testing is always indispensible Must read Java Concurrency in Practice (JCiP)
Thank You!!!
[ JSR 133 (Java Memory Model) FAQ ] https://www.cs.umd.edu/~pugh/java/ memoryModel/jsr-133-faq.html [ Java Concurrency in Practice ] http://jcip.net/ [ Concurrent Programming in Java ] http://gee.cs.oswego.edu/dl/cpj/ [ The JSR-133 Cookbook for Compiler Writers ] http://gee.cs.oswego.edu/dl/jmm/cook book.html [ PrintAssembly ] https://wiki.openjdk.java.net/display/H otSpot/PrintAssembly [ BASIC DISASSEMBLER PLUGIN FOR HOTSPOT DOWNLOADS ] https://kenai.com/projects/base- hsdis/downloads References
Session Survey Help us make the content even better. Please complete the session survey in the Mobile App. Copyright © 2019 Oracle and/or its affiliates.
The preceding is intended to outline our general product direction. It is intended for information purposes only, and may not be incorporated into any contract. It is not a commitment to deliver any material, code, or functionality, and should not be relied upon in making purchasing decisions. The development, release, timing, and pricing of any features or functionality described for Oracle’s products may change and remains at the sole discretion of Oracle Corporation. Statements in this presentation relating to Oracle’s future plans, expectations, beliefs, intentions and prospects are “forward-looking statements” and are subject to material risks and uncertainties. A detailed discussion of these factors and other risks that affect our business is contained in Oracle’s Securities and Exchange Commission (SEC) filings, including our most recent reports on Form 10-K and Form 10-Q under the heading “Risk Factors.” These filings are available on the SEC’s website or on Oracle’s website at http://www.oracle.com/investor. All information in this presentation is current as of September 2019 and Oracle undertakes no duty to update any statement in light of new information or future events. Safe Harbor Copyright © 2019 Oracle and/or its affiliates.

More Related Content

PDF
Hangs, Slowdowns, Starvation—Oh My! A Deep Dive into the Life of a Java Threa...
byDavid Buck
 
PPTX
Java EE 7 for Real Enterprise Systems
byHirofumi Iwasaki
 
PDF
Java Bytecode Crash Course [Code One 2019]
byDavid Buck
 
PDF
JDK Mission Control: Where We Are, Where We Are Going [Code One 2019]
byDavid Buck
 
PDF
Hotspot & AOT
byDmitry Chuyko
 
PDF
CSI (Crash Scene Investigation) HotSpot: Common JVM Crash Causes and Solution...
byDavid Buck
 
PDF
invokedynamic for Mere Mortals [Code One 2019]
byDavid Buck
 
PPTX
Future of Java EE with Java SE 8
byHirofumi Iwasaki
 
Hangs, Slowdowns, Starvation—Oh My! A Deep Dive into the Life of a Java Threa...
byDavid Buck
 
Java EE 7 for Real Enterprise Systems
byHirofumi Iwasaki
 
Java Bytecode Crash Course [Code One 2019]
byDavid Buck
 
JDK Mission Control: Where We Are, Where We Are Going [Code One 2019]
byDavid Buck
 
Hotspot & AOT
byDmitry Chuyko
 
CSI (Crash Scene Investigation) HotSpot: Common JVM Crash Causes and Solution...
byDavid Buck
 
invokedynamic for Mere Mortals [Code One 2019]
byDavid Buck
 
Future of Java EE with Java SE 8
byHirofumi Iwasaki
 

What's hot

PPTX
Hacking Oracle From Web Apps 1 9
bysumsid1234
 
PDF
How to reverse engineer Android applications
byhubx
 
PDF
Compile ahead of time. It's fine?
byDmitry Chuyko
 
PDF
J9: Under the hood of the next open source JVM
byDanHeidinga
 
PPTX
HotSpotコトハジメ
byYasumasa Suenaga
 
PDF
Haj 4344-java se 9 and the application server-1
byKevin Sutter
 
PPTX
FOSDEM 2017 - Open J9 The Next Free Java VM
byCharlie Gracie
 
PDF
Jigsaw modularity
bySrinivasan Raghavan
 
PDF
JavaOne 2016: Life after Modularity
byDanHeidinga
 
PDF
Java EE 7: Boosting Productivity and Embracing HTML5
byArun Gupta
 
PDF
JDK9 Features (Summary, 31/Jul/2015) #JJUG
byYuji Kubota
 
PDF
Hierarchy Viewer Internals
byKyungmin Lee
 
ODP
Javaee6 Overview
byCarol McDonald
 
PDF
Clone Clone Make: a better way to build
byDanHeidinga
 
PDF
Building a web application with ontinuation monads
bySeitaro Yuuki
 
PDF
Flavors of Concurrency in Java
byJavaDayUA
 
PPTX
An Overview of Project Jigsaw
byRafael Winterhalter
 
PDF
CompletableFuture уже здесь
byDmitry Chuyko
 
PDF
J9's MethodHandle Compilation Pipeline #JFokus2015
byDanHeidinga
 
PDF
Java EE 7: Whats New in the Java EE Platform @ Devoxx 2013
byArun Gupta
 
Hacking Oracle From Web Apps 1 9
bysumsid1234
 
How to reverse engineer Android applications
byhubx
 
Compile ahead of time. It's fine?
byDmitry Chuyko
 
J9: Under the hood of the next open source JVM
byDanHeidinga
 
HotSpotコトハジメ
byYasumasa Suenaga
 
Haj 4344-java se 9 and the application server-1
byKevin Sutter
 
FOSDEM 2017 - Open J9 The Next Free Java VM
byCharlie Gracie
 
Jigsaw modularity
bySrinivasan Raghavan
 
JavaOne 2016: Life after Modularity
byDanHeidinga
 
Java EE 7: Boosting Productivity and Embracing HTML5
byArun Gupta
 
JDK9 Features (Summary, 31/Jul/2015) #JJUG
byYuji Kubota
 
Hierarchy Viewer Internals
byKyungmin Lee
 
Javaee6 Overview
byCarol McDonald
 
Clone Clone Make: a better way to build
byDanHeidinga
 
Building a web application with ontinuation monads
bySeitaro Yuuki
 
Flavors of Concurrency in Java
byJavaDayUA
 
An Overview of Project Jigsaw
byRafael Winterhalter
 
CompletableFuture уже здесь
byDmitry Chuyko
 
J9's MethodHandle Compilation Pipeline #JFokus2015
byDanHeidinga
 
Java EE 7: Whats New in the Java EE Platform @ Devoxx 2013
byArun Gupta
 

Similar to Java Concurrency, A(nother) Peek Under the Hood [Code One 2019]

PDF
Java Memory Model
byŁukasz Koniecki
 
PDF
Java Threads: Lightweight Processes
byIsuru Perera
 
PDF
jvm/java - towards lock-free concurrency
byArvind Kalyan
 
PPTX
The Java memory model made easy
byRafael Winterhalter
 
PDF
Concurrency on the JVM
byBernhard Huemer
 
PPTX
Jvm memory model
byYoav Avrahami
 
PDF
Programming with Threads in Java
bykoji lin
 
PDF
Java Concurrency and Performance | Multi Threading | Concurrency | Java Conc...
byAnand Narayanan
 
PDF
Concurrent Programming in Java
byLakshmi Narasimhan
 
KEY
Modern Java Concurrency
byBen Evans
 
KEY
Modern Java Concurrency (Devoxx Nov/2011)
byMartijn Verburg
 
PDF
Concurrency in Java
byLakshmi Narasimhan
 
PDF
Java Concurrency, A(nother) Peek Under the Hood [JavaOne 2016 CON1497]
byDavid Buck
 
PPT
Java Core | Modern Java Concurrency | Martijn Verburg & Ben Evans
byJAX London
 
PPTX
Does Java Have a Future After Version 8? (Belfast JUG April 2014)
byGarth Gilmour
 
ODP
Java Concurrency
byCarol McDonald
 
PDF
Concurrency
byIsaac Liao
 
PDF
Java Concurrency in Practice
byAlina Dolgikh
 
KEY
Modern Java Concurrency (OSCON 2012)
byMartijn Verburg
 
PDF
An End to Order
byRobert Burrell Donkin
 
Java Memory Model
byŁukasz Koniecki
 
Java Threads: Lightweight Processes
byIsuru Perera
 
jvm/java - towards lock-free concurrency
byArvind Kalyan
 
The Java memory model made easy
byRafael Winterhalter
 
Concurrency on the JVM
byBernhard Huemer
 
Jvm memory model
byYoav Avrahami
 
Programming with Threads in Java
bykoji lin
 
Java Concurrency and Performance | Multi Threading | Concurrency | Java Conc...
byAnand Narayanan
 
Concurrent Programming in Java
byLakshmi Narasimhan
 
Modern Java Concurrency
byBen Evans
 
Modern Java Concurrency (Devoxx Nov/2011)
byMartijn Verburg
 
Concurrency in Java
byLakshmi Narasimhan
 
Java Concurrency, A(nother) Peek Under the Hood [JavaOne 2016 CON1497]
byDavid Buck
 
Java Core | Modern Java Concurrency | Martijn Verburg & Ben Evans
byJAX London
 
Does Java Have a Future After Version 8? (Belfast JUG April 2014)
byGarth Gilmour
 
Java Concurrency
byCarol McDonald
 
Concurrency
byIsaac Liao
 
Java Concurrency in Practice
byAlina Dolgikh
 
Modern Java Concurrency (OSCON 2012)
byMartijn Verburg
 
An End to Order
byRobert Burrell Donkin
 

More from David Buck

PDF
Java Concurrency, A(nother) Peek Under the Hood [Java Day Tokyo 2016 3-C]
byDavid Buck
 
PDF
HotSpot のロック: A Peek Under the Hood [JJUG ナイトセミナ JVM 特集 ２０１５年８月]
byDavid Buck
 
PDF
Everything You Wanted to Know About JIT Compilation but Were Afraid to Ask [J...
byDavid Buck
 
PDF
Bytecode Verification, the Hero That Java Needs [JavaOne 2016 CON1500]
byDavid Buck
 
PDF
Z Garbage Collector
byDavid Buck
 
PDF
Let’s Write Our Own Chip-8 Interpreter! [JavaOne 2017 CON3584]
byDavid Buck
 
PDF
JDK Mission Control: Where We Are, Where We Are Going [Groundbreakers APAC 20...
byDavid Buck
 
PDF
Lambda: A Peek Under The Hood [Java Day Tokyo 2015 6-3]
byDavid Buck
 
PDF
Java Debuggers: A Peek Under the Hood [JavaOne 2016 CON1503]
byDavid Buck
 
PDF
Java SE 8におけるHotSpotの進化 [Java Day Tokyo 2014 C-2]
byDavid Buck
 
PPTX
OpenJDK 参加入門 [JJUG CCC 2017 Fall E2]
byDavid Buck
 
PDF
JDK 13 New Features [MeetUp with Java Experts! @Gaienmae/Dojima 2019]
byDavid Buck
 
PDF
HotSpot Synchronization, A Peek Under the Hood [JavaOne 2015 CON7570]
byDavid Buck
 
PDF
Full Speed Ahead! (Ahead-of-Time Compilation for Java SE) [JavaOne 2017 CON3738]
byDavid Buck
 
PPTX
OpenJDK: How to Join In on All the Fun [JavaOne 2017 CON3667]
byDavid Buck
 
PDF
Var handles jjug_ccc_spring_2018
byDavid Buck
 
PDF
InvokeDynamic for Mere Mortals [JavaOne 2015 CON7682]
byDavid Buck
 
PDF
Valhalla Update JJUG CCC Spring 2019
byDavid Buck
 
PDF
Ahead-of-Time Compilation with JDK 9 [Java Day Tokyo 2017 D1-A1]
byDavid Buck
 
PDF
JDK 10 へようこそ
byDavid Buck
 
Java Concurrency, A(nother) Peek Under the Hood [Java Day Tokyo 2016 3-C]
byDavid Buck
 
HotSpot のロック: A Peek Under the Hood [JJUG ナイトセミナ JVM 特集 ２０１５年８月]
byDavid Buck
 
Everything You Wanted to Know About JIT Compilation but Were Afraid to Ask [J...
byDavid Buck
 
Bytecode Verification, the Hero That Java Needs [JavaOne 2016 CON1500]
byDavid Buck
 
Z Garbage Collector
byDavid Buck
 
Let’s Write Our Own Chip-8 Interpreter! [JavaOne 2017 CON3584]
byDavid Buck
 
JDK Mission Control: Where We Are, Where We Are Going [Groundbreakers APAC 20...
byDavid Buck
 
Lambda: A Peek Under The Hood [Java Day Tokyo 2015 6-3]
byDavid Buck
 
Java Debuggers: A Peek Under the Hood [JavaOne 2016 CON1503]
byDavid Buck
 
Java SE 8におけるHotSpotの進化 [Java Day Tokyo 2014 C-2]
byDavid Buck
 
OpenJDK 参加入門 [JJUG CCC 2017 Fall E2]
byDavid Buck
 
JDK 13 New Features [MeetUp with Java Experts! @Gaienmae/Dojima 2019]
byDavid Buck
 
HotSpot Synchronization, A Peek Under the Hood [JavaOne 2015 CON7570]
byDavid Buck
 
Full Speed Ahead! (Ahead-of-Time Compilation for Java SE) [JavaOne 2017 CON3738]
byDavid Buck
 
OpenJDK: How to Join In on All the Fun [JavaOne 2017 CON3667]
byDavid Buck
 
Var handles jjug_ccc_spring_2018
byDavid Buck
 
InvokeDynamic for Mere Mortals [JavaOne 2015 CON7682]
byDavid Buck
 
Valhalla Update JJUG CCC Spring 2019
byDavid Buck
 
Ahead-of-Time Compilation with JDK 9 [Java Day Tokyo 2017 D1-A1]
byDavid Buck
 
JDK 10 へようこそ
byDavid Buck
 

Recently uploaded

PDF
Breaking the Vulnerability Management Cycle with Anchore and Echo
byAnchore
 
PPTX
Building AI agents in Java - Devoxx Belgium 2025
byJulien Dubois
 
PPTX
Building a RAG System for Customer Support - L1
byBogdan Mustata
 
PDF
IAAM Meetup #7 chez Onepoint - Construire un Rag-as-a-service en production. ...
byiaaixmarseille
 
PDF
Bring AI and build AI agents into your Jakarta EE Apps with LangChain4J-CDI
byBuhake Sindi
 
PPTX
The Sync Strikes Back: Tales from the MOPs Trenches
bybbedford2
 
PDF
DSD-INT 2025 MeshKernel and D-Grid Editor - Stout
byDeltares
 
PPTX
Presentation on AWS Cloud RDS Deep dive
byBimal Jain
 
PDF
inSis suite - Laboratory Information Management System
byKondapi V Siva Rama Brahmam
 
PPTX
operating sys about shells and terminals commands .pptx
byYazeedAbdullah6
 
PPTX
CRM Development Company | Custom CRM Development Services
byyugababu033
 
PDF
SCORM Cloud: The 5 categories of content distribution
byRustici Software
 
PDF
Data Integration with Salesforce Bootcamp
byDele Amefo
 
PDF
Presentation Empowerment Technology in ICT
byoryoseiii
 
PDF
DSD-INT 2025 Century-Scale Impacts of Sediment-Based Coastal Restoration unde...
byDeltares
 
PDF
DSD-INT 2025 Hydrodynamic and Morphodynamic Modeling with Delft3D FM for an I...
byDeltares
 
PDF
Internship Project Training Report-3.pdf
byPawank36
 
PDF
DSD-INT 2025 3D-modelling of salt intrusion into Germany’s busiest waterway -...
byDeltares
 
PDF
DSD-INT 2025 UK Coastal Flooding Incident Guide - Dam
byDeltares
 
PDF
DSD-INT 2025 Climate and impact attribution of compound flooding induced by t...
byDeltares
 
Breaking the Vulnerability Management Cycle with Anchore and Echo
byAnchore
 
Building AI agents in Java - Devoxx Belgium 2025
byJulien Dubois
 
Building a RAG System for Customer Support - L1
byBogdan Mustata
 
IAAM Meetup #7 chez Onepoint - Construire un Rag-as-a-service en production. ...
byiaaixmarseille
 
Bring AI and build AI agents into your Jakarta EE Apps with LangChain4J-CDI
byBuhake Sindi
 
The Sync Strikes Back: Tales from the MOPs Trenches
bybbedford2
 
DSD-INT 2025 MeshKernel and D-Grid Editor - Stout
byDeltares
 
Presentation on AWS Cloud RDS Deep dive
byBimal Jain
 
inSis suite - Laboratory Information Management System
byKondapi V Siva Rama Brahmam
 
operating sys about shells and terminals commands .pptx
byYazeedAbdullah6
 
CRM Development Company | Custom CRM Development Services
byyugababu033
 
SCORM Cloud: The 5 categories of content distribution
byRustici Software
 
Data Integration with Salesforce Bootcamp
byDele Amefo
 
Presentation Empowerment Technology in ICT
byoryoseiii
 
DSD-INT 2025 Century-Scale Impacts of Sediment-Based Coastal Restoration unde...
byDeltares
 
DSD-INT 2025 Hydrodynamic and Morphodynamic Modeling with Delft3D FM for an I...
byDeltares
 
Internship Project Training Report-3.pdf
byPawank36
 
DSD-INT 2025 3D-modelling of salt intrusion into Germany’s busiest waterway -...
byDeltares
 
DSD-INT 2025 UK Coastal Flooding Incident Guide - Dam
byDeltares
 
DSD-INT 2025 Climate and impact attribution of compound flooding induced by t...
byDeltares
 

Java Concurrency, A(nother) Peek Under the Hood [Code One 2019]

  • 1.
    The following isintended to outline our general product direction. It is intended for information purposes only, and may not be incorporated into any contract. It is not a commitment to deliver any material, code, or functionality, and should not be relied upon in making purchasing decisions. The development, release, timing, and pricing of any features or functionality described for Oracle’s products may change and remains at the sole discretion of Oracle Corporation. Statements in this presentation relating to Oracle’s future plans, expectations, beliefs, intentions and prospects are “forward-looking statements” and are subject to material risks and uncertainties. A detailed discussion of these factors and other risks that affect our business is contained in Oracle’s Securities and Exchange Commission (SEC) filings, including our most recent reports on Form 10-K and Form 10-Q under the heading “Risk Factors.” These filings are available on the SEC’s website or on Oracle’s website at http://www.oracle.com/investor. All information in this presentation is current as of September 2019 and Oracle undertakes no duty to update any statement in light of new information or future events. Safe Harbor Copyright © 2019 Oracle and/or its affiliates.
  • 2.
    Java Concurrency, A(nother) PeekUnder the Hood [DEV4211] Principal Member of Technical Staff Java Platform Group September 19, 2019 David Buck Copyright © 2019 Oracle and/or its affiliates.
  • 3.
    IoT Microservices DevOpsin the Cloud Copyright © 2019 Oracle and/or its affiliates.
  • 4.
    IoT Microservices DevOpsin the Cloud Copyright © 2019 Oracle and/or its affiliates.
  • 5.
    IoT Microservices DevOpsin the Cloud Copyright © 2019 Oracle and/or its affiliates.
  • 6.
    JVM Sustaining Engineer OpenJDKUpdate Project Maintainer JavaOne Rock Star Co-author of Oracle WebLogic Server 11g 構築・運用ガイド @DavidBuckJP https://blogs.oracle.com/buck/ Who am I? David Buck (left)
  • 7.
    Program Agenda Introduction Background Tangent 1:Special Relativity History Implementation Tangent 2: HSDIS Future Conclusions 1 2 3 4 5 7 6
  • 8.
  • 9.
    Motivation “But I don’twrite multithreaded code…”
  • 10.
    Web Server picture: Coolcaesarat the English language Wikipedia [GFDL (http://www.gnu.org/copyleft/fdl.html) or CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0/)]
  • 11.
  • 12.
    Libraries picture: David Vignoni/ ICON KING (http://icon-king.com) [LGPL (http://www.gnu.org/licenses/lgpl.html) or LGPL (http://www.gnu.org/licenses/lgpl.html)]
  • 13.
    Batch Processing picture: USSocial Security Administration (http://www.ssa.gov/history/acalcs.html) [Public domain]
  • 14.
    “But I don’twrite multithreaded code…”
  • 15.
    “But I don’twrite multithreaded code…”
  • 16.
    Race Conditions picture: Sakuramboat English Wikipedia [GFDL (http://www.gnu.org/copyleft/fdl.html) or CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0/)]
  • 17.
    Heisenbugs Bug Heisenberg Heisenbug picture: Bundesarchiv,Bild 183-R57262 / Unknown / CC-BY-SA 3.0 [CC BY-SA 3.0 de (http://creativecommons.org/licenses/by-sa/3.0/de/deed.en)]
  • 18.
    Observer Effect picture: ChristianSchirm (Own work) [CC0]
  • 19.
    Avoiding Heisenbugs Java MemoryModel synchronized keyword java.util.concurrent
  • 20.
    Avoiding Heisenbugs Java MemoryModel synchronized keyword java.util.concurrent • Don’t do ＸＸＸ • You must do ＹＹＹ
  • 21.
    a² + b²== c²
  • 22.
    picture: WTF PublicLicense, Version 2
  • 23.
  • 24.
  • 25.
    Memory Model Definition 1 Specificationthat explains when we can guarantee that a written value may be read correctly
  • 26.
    void hogeMethod1() { intlocalA = 42; assert localA == 42; }
  • 27.
    static int staticA; voidhogeMethod2() { staticA = 42; assert staticA == 42; }
  • 28.
    int data =0; boolean ready = false; void hoge3() { while (!ready) {}; assert data == 42; } void hoge4() { data = 42; ready = true; }
  • 29.
  • 30.
  • 31.
    Memory Ordering void hoge5(){ a = 1; b = 2; c = 3; d = 4; e = 5; a = a + 1; }
  • 32.
    Memory Ordering void hoge5(){ a = 1; b = 2; c = 3; d = 4; e = 5; a = a + 1; } void hoge5() { a = 2; b = 2; c = 3; d = 4; e = 5; }
  • 33.
    Memory Ordering void hoge5(){ a = 1; b = 2; c = 3; d = 4; e = 5; a = a + 1; } void hoge5() { b = 2; c = 3; d = 4; e = 5; a = 2; }
  • 34.
  • 35.
    Out of OrderExecution picture: Amit6, original version (File:Superscalarpipeline.png) by User:Poil (Own work) [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0)]
  • 36.
    CPU Differences Type AlphaARMv7 PA- RISC POWER SPARC RMO SPARC PSO SPARC TSO x86 x86 oostore AMD64 IA-64 zSeries load- load Y Y Y Y Y Y Y load- store Y Y Y Y Y Y Y store- store Y Y Y Y Y Y Y Y store- load Y Y Y Y Y Y Y Y Y Y Y Y Atomic (loads) Y Y Y Y Y Atomic (stores) Y Y Y Y Y Y Depend ent loads Y instruct ion cache Y Y Y Y Y Y Y Y Y Y chart source: https://en.wikipedia.org/wiki/Memory_ordering
  • 37.
  • 38.
  • 39.
    Memory Barriers int data= 0; boolean ready = false; void hoge3() { while (!ready) {}; assert data == 42; } void hoge4() { data = 42; ready = true; }
  • 40.
    Memory Barriers int data= 0; boolean ready = false; void hoge3() { while (!ready) {}; assert data == 42; } void hoge4() { data = 42; ready = true; }
  • 41.
    Memory Barriers int data= 0; boolean ready = false; void hoge3() { while (!ready) {}; assert data == 42; } void hoge4() { data = 42; ready = true; }
  • 42.
  • 43.
  • 45.
    Tangent 1: SpecialRelativity picture: Sakurambo (Own work) [Public domain]
  • 46.
    Tangent 1: SpecialRelativity A B C
  • 47.
    Tangent 1: SpecialRelativity A B C A, B, C
  • 48.
    Tangent 1: SpecialRelativity A B C A, B, C C, B, A
  • 49.
    Tangent 1: SpecialRelativity Observed order depends on viewer's frame of reference A B C A, B, C C, B, A
  • 50.
    No single “correct”timeline Special Relativity Observed order of events depends on frame of reference
  • 51.
    No single “correct”timeline Special Relativity Observed order of events depends on frame of reference Multithreaded Code Observed order of events depends on thread
  • 52.
    Memory Model Definition 2 Clarifywhat multithreaded behavior developers may depend on
  • 53.
    Memory Model Definition 2 Clarifywhat multithreaded behavior developers may depend on Limits what types of optimizations the runtime may do
  • 54.
  • 55.
    Java Memory Model(JMM) Write once, run anywhere 1995 Part of the formal language specification Happened-before picture: Peter Campbell [GFDL (http://www.gnu.org/copyleft/fdl.html) or CC BY-SA 4.0-3.0-2.5-2.0-1.0 (http://creativecommons.org/licenses/by-sa/4.0-3.0-2.5-2.0-1.0)]
  • 56.
  • 57.
    Leslie Lamport LaTex happened-before picture: LeslieLamport [GFDL (http://en.wikipedia.org/wiki/GFDL]
  • 58.
    happened-before void hoge5() { a= 1; b = 2; c = 3; d = 4; e = 5; a = a + 1; }
  • 59.
    happened-before void hoge4() { data= 42; ready = true; } void hoge3() { while (!ready) {}; assert data == 42; }
  • 60.
    happened-before void hoge4() { data= 42; ready = true; } void hoge3() { while (!ready) {}; assert data == 42; }
  • 61.
    happened-before void synchronized hoge4(){ data = 42; ready = true; } void synchronized hoge3() { while (!ready) {}; assert data == 42; } Warning: if hoge3 is executed first, the above code will deadlock
  • 62.
    happened-before void synchronized hoge4() { data= 42; ready = true; } void synchronized hoge3() { while (!ready) {}; assert data == 42; } Warning: if hoge3 is executed first, the above code will deadlock
  • 63.
  • 64.
  • 65.
    Original JMM Keywords synchronized mutualexclusion happened-before volatile Visibility
  • 66.
    Problems with theOriginal JMM volatile does not establish a happened-before relationship final values can change Many important runtime optimization were not allowed
  • 67.
    Doug Lea Author ofthe Java Multithreaded bible Introduced his own OSS high- level multithreaded library
  • 68.
    Java SE 5.0 ModernJMM introduced Lea’s library added to official JDK picture: Zvi Roger [CC BY 3.0 (http://creativecommons.org/licenses/by/3.0)]
  • 69.
    Modern JMM JSR-133 Fixed shortcomingsin original JMM volatile does establish happens-before final values will never change
  • 70.
    Modern JMM Keywords synchronized mutualexclusion happened-before volatile visibility happened-before final immutability
  • 71.
    JSR-133 の volatile voidhoge4() { data = 42; ready = true; } void hoge3() { while (!ready) {}; assert data == 42; } Warning: if hoge3 is executed first, the above code will deadlock volatile boolean ready = false;
  • 72.
    volatile != atomic volatileint id = 0; int incID() { return id++; }
  • 73.
    volatile != atomic volatileint id = 0; int incID() { return id++; } reg = [id] reg++ [id] = reg
  • 74.
    volatile != atomic volatileint id = 0; synchronized int incID() { return id++; }
  • 75.
    64-bit updates arenot guaranteed atomic • Reads and Writes to long and double values may not happen atomically • Possible to read a mix of two different writes Copyright © 2019 Oracle and/or its affiliates. Old value MSB New value LSB
  • 76.
    happened-before Monitor (acquisition /release) Volatile (read / write) final “freeze” (constructor) JNI System.out.println（） Input / Output thread start()/join() operations on j.u.concurrent collections
  • 77.
  • 78.
  • 79.
  • 80.
    Functional Programming (JDK8) Lambda Forms Stream API λ
  • 81.
    Var Handles • Lower-levelthan volatile / final • Allows a value to be volatile only when we want it to be • Explicate fence and acquire / release semantics • Added in JDK 9 to replace several use cases previously only supported with sun.misc.Unsafe Copyright © 2019 Oracle and/or its affiliates.
  • 82.
  • 83.
    Tangent 2: HSDIS(HotSpot Disassembler) Lets us see code generated by JIT Requires a disassembler plugin GNU binutils-based plugin base-hsdis Command line options +PrintAssembly +CompileCommand=print,*MyClass.myMethod
  • 84.
  • 85.
  • 86.
    ARM Assembly CrashCourse Op Target Source
  • 87.
    ARM Assembly CrashCourse MOV r02 #42
  • 88.
    ARM Assembly CrashCourse MOV r02 #42 r02 = 42
  • 89.
    ARM Assembly CrashCourse Op Target Source
  • 90.
    ARM Assembly CrashCourse Op Target Source Exception STR Source Target
  • 91.
    ARM Assembly CrashCourse MOV Copies registers MOV r02 r03 Writes Literals MOV r02 #42
  • 92.
    ARM Assembly CrashCourse LDx Loads data from memory to a register ldr r03, [r06] r03 = *r06
  • 93.
    ARM Assembly CrashCourse CMP / BEQ Compare and branch if equal cmp r0, #0 beq 0x74178d08 if (r0 == 0) goto 0x74178d08
  • 94.
    ARM Assembly CrashCourse DMB Data Memory Barrier dmb st dmb sy
  • 95.
  • 96.
    Safe Points Methods proactivelypoll JVM makes page unreadable to stop the world movw ip, #45056 ; 0xb000 movt ip, #30461 ; 0x76fd ldr ip, [ip] ; {poll_return}
  • 97.
    Long Value static longval = 0; public static void main(String[] args) { new Thread(() -> { while(true) val = -1L; } ).start(); new Thread(() -> { while(true) val = 0L; } ).start(); while (true) { long temp = val; if ( temp != -1 && temp != 0 ) { System.out.println("temp (DEC): " + temp); System.out.println("temp (BIN): " + Long.toBinaryString(temp)); System.exit(-1); } } }
  • 98.
    Object Initialization public classObjInit { static ObjInit globalRef = new ObjInit(); long number; public ObjInit() { number = 42; }
  • 99.
    Object Initialization public staticvoid main(String[] args) { new Thread(() -> { while(true) { long temp = globalRef.number; if (temp != 42) { System.out.println(temp); System.exit(-1); } } } ).start(); new Thread(() -> { while(true) globalRef = new ObjInit(); } ).start(); }}
  • 100.
    public class Loopextends Thread { static boolean done = false; public static void main(String[] args) { Thread childThread = new Loop(); childThread.start(); System.out.println("Starting loop"); spinWait(); System.out.println("Exited loop"); } private static void spinWait() { while (!done) ; } public void run() { try { Thread.sleep(5 * 1000); } catch (Exception e) {} done = true; } } // class Loop Loop
  • 101.
  • 102.
    JEP-188/JMM9 Not delivered withJDK 9 (JMM9 != JDK 9) JVM-level specification Compatibility with C11/C++11 Cover new features added since JDK 5 (e.g. AtomicX.weakCompareAndSet())
  • 103.
  • 104.
  • 105.
    Code against thespecification Intermittent bugs are common Behavior changes with JRE / platform Stuff to avoid synchronized (new Object()) { } Randomly adding volatile declarations until it magically starts working
  • 106.
    Testing As close toproduction environment as possible Same hardware Same JRE (including version） Same settings
  • 107.
    Testing As much varietyas possible Various hardware Various JREs (including version） Various settings
  • 108.
    Java Concurrency inPractice Java Concurrency Bible Covers JSR-133 / JSR-166
  • 109.
    Summary Avoid low-level APIs Codeagainst the standard, not the implementation Testing is always indispensible Must read Java Concurrency in Practice (JCiP)
  • 110.
  • 111.
    [ JSR 133(Java Memory Model) FAQ ] https://www.cs.umd.edu/~pugh/java/ memoryModel/jsr-133-faq.html [ Java Concurrency in Practice ] http://jcip.net/ [ Concurrent Programming in Java ] http://gee.cs.oswego.edu/dl/cpj/ [ The JSR-133 Cookbook for Compiler Writers ] http://gee.cs.oswego.edu/dl/jmm/cook book.html [ PrintAssembly ] https://wiki.openjdk.java.net/display/H otSpot/PrintAssembly [ BASIC DISASSEMBLER PLUGIN FOR HOTSPOT DOWNLOADS ] https://kenai.com/projects/base- hsdis/downloads References
  • 112.
    Session Survey Help usmake the content even better. Please complete the session survey in the Mobile App. Copyright © 2019 Oracle and/or its affiliates.
  • 113.
    The preceding isintended to outline our general product direction. It is intended for information purposes only, and may not be incorporated into any contract. It is not a commitment to deliver any material, code, or functionality, and should not be relied upon in making purchasing decisions. The development, release, timing, and pricing of any features or functionality described for Oracle’s products may change and remains at the sole discretion of Oracle Corporation. Statements in this presentation relating to Oracle’s future plans, expectations, beliefs, intentions and prospects are “forward-looking statements” and are subject to material risks and uncertainties. A detailed discussion of these factors and other risks that affect our business is contained in Oracle’s Securities and Exchange Commission (SEC) filings, including our most recent reports on Form 10-K and Form 10-Q under the heading “Risk Factors.” These filings are available on the SEC’s website or on Oracle’s website at http://www.oracle.com/investor. All information in this presentation is current as of September 2019 and Oracle undertakes no duty to update any statement in light of new information or future events. Safe Harbor Copyright © 2019 Oracle and/or its affiliates.