393 lines
14 KiB
XML
393 lines
14 KiB
XML
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<?xml version="1.0"?>
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<ruleset name="Multithreading"
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xmlns="http://pmd.sourceforge.net/ruleset/2.0.0"
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xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
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xsi:schemaLocation="http://pmd.sourceforge.net/ruleset/2.0.0 https://pmd.sourceforge.io/ruleset_2_0_0.xsd">
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<description>
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Rules that flag issues when dealing with multiple threads of execution.
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</description>
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<rule name="AvoidSynchronizedAtMethodLevel"
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language="java"
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since="3.0"
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message="Use block level rather than method level synchronization"
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class="net.sourceforge.pmd.lang.rule.XPathRule"
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externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_multithreading.html#avoidsynchronizedatmethodlevel">
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<description>
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Method-level synchronization can cause problems when new code is added to the method.
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Block-level synchronization helps to ensure that only the code that needs synchronization
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gets it.
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</description>
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<priority>3</priority>
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<properties>
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<property name="xpath">
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<value>//MethodDeclaration[@Synchronized='true']</value>
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</property>
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</properties>
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<example>
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<![CDATA[
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public class Foo {
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// Try to avoid this:
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synchronized void foo() {
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}
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// Prefer this:
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void bar() {
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synchronized(this) {
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}
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}
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// Try to avoid this for static methods:
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static synchronized void fooStatic() {
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}
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// Prefer this:
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static void barStatic() {
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synchronized(Foo.class) {
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}
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}
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}
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]]>
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</example>
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</rule>
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<rule name="AvoidThreadGroup"
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language="java"
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since="3.6"
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message="Avoid using java.lang.ThreadGroup; it is not thread safe"
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class="net.sourceforge.pmd.lang.rule.XPathRule"
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typeResolution="true"
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externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_multithreading.html#avoidthreadgroup">
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<description>
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Avoid using java.lang.ThreadGroup; although it is intended to be used in a threaded environment
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it contains methods that are not thread-safe.
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</description>
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<priority>3</priority>
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<properties>
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<property name="xpath">
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<value>
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<![CDATA[
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//AllocationExpression/ClassOrInterfaceType[pmd-java:typeIs('java.lang.ThreadGroup')]|
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//PrimarySuffix[contains(@Image, 'getThreadGroup')]
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]]>
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</value>
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</property>
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</properties>
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<example>
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<![CDATA[
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public class Bar {
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void buz() {
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ThreadGroup tg = new ThreadGroup("My threadgroup");
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tg = new ThreadGroup(tg, "my thread group");
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tg = Thread.currentThread().getThreadGroup();
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tg = System.getSecurityManager().getThreadGroup();
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}
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}
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]]>
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</example>
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</rule>
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<rule name="AvoidUsingVolatile"
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language="java"
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since="4.1"
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class="net.sourceforge.pmd.lang.rule.XPathRule"
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message="Use of modifier volatile is not recommended."
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externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_multithreading.html#avoidusingvolatile">
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<description>
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Use of the keyword 'volatile' is generally used to fine tune a Java application, and therefore, requires
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a good expertise of the Java Memory Model. Moreover, its range of action is somewhat misknown. Therefore,
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the volatile keyword should not be used for maintenance purpose and portability.
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</description>
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<priority>2</priority>
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<properties>
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<property name="xpath">
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<value>//FieldDeclaration[contains(@Volatile,'true')]</value>
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</property>
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</properties>
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<example>
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<![CDATA[
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public class ThrDeux {
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private volatile String var1; // not suggested
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private String var2; // preferred
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}
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]]>
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</example>
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</rule>
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<rule name="DoNotUseThreads"
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language="java"
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since="4.1"
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class="net.sourceforge.pmd.lang.rule.XPathRule"
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message="To be compliant to J2EE, a webapp should not use any thread."
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externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_multithreading.html#donotusethreads">
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<description>
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The J2EE specification explicitly forbids the use of threads.
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</description>
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<priority>3</priority>
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<properties>
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<property name="xpath">
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<value>//ClassOrInterfaceType[@Image = 'Thread' or @Image = 'Runnable']</value>
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</property>
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</properties>
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<example>
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<![CDATA[
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// This is not allowed
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public class UsingThread extends Thread {
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}
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// Neither this,
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public class OtherThread implements Runnable {
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// Nor this ...
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public void methode() {
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Runnable thread = new Thread(); thread.run();
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}
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}
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]]>
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</example>
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</rule>
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<rule name="DontCallThreadRun"
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language="java"
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since="4.3"
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message="Don't call Thread.run() explicitly, use Thread.start()"
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class="net.sourceforge.pmd.lang.rule.XPathRule"
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typeResolution="true"
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externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_multithreading.html#dontcallthreadrun">
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<description>
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Explicitly calling Thread.run() method will execute in the caller's thread of control. Instead, call Thread.start() for the intended behavior.
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</description>
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<priority>4</priority>
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<properties>
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<property name="xpath">
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<value>
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<![CDATA[
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//StatementExpression/PrimaryExpression
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[
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PrimaryPrefix
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[
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./Name[ends-with(@Image, '.run') or @Image = 'run']
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and substring-before(Name/@Image, '.') =//VariableDeclarator/VariableDeclaratorId/@Image
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[../../../Type/ReferenceType/ClassOrInterfaceType[pmd-java:typeIs('java.lang.Thread')]]
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or (./AllocationExpression/ClassOrInterfaceType[pmd-java:typeIs('java.lang.Thread')]
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and ../PrimarySuffix[@Image = 'run'])
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]
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]
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]]>
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</value>
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</property>
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</properties>
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<example>
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<![CDATA[
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Thread t = new Thread();
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t.run(); // use t.start() instead
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new Thread().run(); // same violation
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]]>
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</example>
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</rule>
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<rule name="DoubleCheckedLocking"
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language="java"
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since="1.04"
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message="Double checked locking is not thread safe in Java."
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class="net.sourceforge.pmd.lang.java.rule.multithreading.DoubleCheckedLockingRule"
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externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_multithreading.html#doublecheckedlocking">
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<description>
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Partially created objects can be returned by the Double Checked Locking pattern when used in Java.
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An optimizing JRE may assign a reference to the baz variable before it calls the constructor of the object the
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reference points to.
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Note: With Java 5, you can make Double checked locking work, if you declare the variable to be `volatile`.
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For more details refer to: <http://www.javaworld.com/javaworld/jw-02-2001/jw-0209-double.html>
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or <http://www.cs.umd.edu/~pugh/java/memoryModel/DoubleCheckedLocking.html>
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</description>
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<priority>1</priority>
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<example>
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<![CDATA[
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public class Foo {
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/*volatile */ Object baz = null; // fix for Java5 and later: volatile
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Object bar() {
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if (baz == null) { // baz may be non-null yet not fully created
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synchronized(this) {
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if (baz == null) {
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baz = new Object();
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}
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}
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}
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return baz;
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}
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}
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]]>
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</example>
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</rule>
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<rule name="NonThreadSafeSingleton"
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since="3.4"
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message="Singleton is not thread safe"
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class="net.sourceforge.pmd.lang.java.rule.multithreading.NonThreadSafeSingletonRule"
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externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_multithreading.html#nonthreadsafesingleton">
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<description>
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Non-thread safe singletons can result in bad state changes. Eliminate
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static singletons if possible by instantiating the object directly. Static
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singletons are usually not needed as only a single instance exists anyway.
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Other possible fixes are to synchronize the entire method or to use an
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[initialize-on-demand holder class](https://en.wikipedia.org/wiki/Initialization-on-demand_holder_idiom).
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Refrain from using the double-checked locking pattern. The Java Memory Model doesn't
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guarantee it to work unless the variable is declared as `volatile`, adding an uneeded
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performance penalty. [Reference](http://www.cs.umd.edu/~pugh/java/memoryModel/DoubleCheckedLocking.html)
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See Effective Java, item 48.
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</description>
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<priority>3</priority>
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<example>
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<![CDATA[
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private static Foo foo = null;
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//multiple simultaneous callers may see partially initialized objects
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public static Foo getFoo() {
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if (foo==null) {
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foo = new Foo();
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}
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return foo;
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}
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]]>
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</example>
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</rule>
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<rule name="UnsynchronizedStaticDateFormatter"
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since="3.6"
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deprecated="true"
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message="Static DateFormatter objects should be accessed in a synchronized manner"
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class="net.sourceforge.pmd.lang.java.rule.multithreading.UnsynchronizedStaticDateFormatterRule"
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externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_multithreading.html#unsynchronizedstaticdateformatter">
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<description>
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SimpleDateFormat instances are not synchronized. Sun recommends using separate format instances
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for each thread. If multiple threads must access a static formatter, the formatter must be
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synchronized either on method or block level.
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This rule has been deprecated in favor of the rule {% rule UnsynchronizedStaticFormatter %}.
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</description>
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<priority>3</priority>
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<example>
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<![CDATA[
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public class Foo {
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private static final SimpleDateFormat sdf = new SimpleDateFormat();
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void bar() {
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sdf.format(); // poor, no thread-safety
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}
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synchronized void foo() {
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sdf.format(); // preferred
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}
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}
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]]>
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</example>
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</rule>
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<rule name="UnsynchronizedStaticFormatter"
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since="6.11.0"
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message="Static Formatter objects should be accessed in a synchronized manner"
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class="net.sourceforge.pmd.lang.java.rule.multithreading.UnsynchronizedStaticFormatterRule"
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externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_multithreading.html#unsynchronizedstaticformatter">
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<description>
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Instances of `java.text.Format` are generally not synchronized.
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Sun recommends using separate format instances for each thread.
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If multiple threads must access a static formatter, the formatter must be
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synchronized either on method or block level.
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</description>
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<priority>3</priority>
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<example>
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<![CDATA[
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public class Foo {
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private static final SimpleDateFormat sdf = new SimpleDateFormat();
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void bar() {
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sdf.format(); // poor, no thread-safety
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}
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synchronized void foo() {
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sdf.format(); // preferred
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}
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}
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]]>
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</example>
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</rule>
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<rule name="UseConcurrentHashMap"
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language="java"
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minimumLanguageVersion="1.5"
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since="4.2.6"
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message="If you run in Java5 or newer and have concurrent access, you should use the ConcurrentHashMap implementation"
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class="net.sourceforge.pmd.lang.rule.XPathRule"
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externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_multithreading.html#useconcurrenthashmap">
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<description>
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Since Java5 brought a new implementation of the Map designed for multi-threaded access, you can
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perform efficient map reads without blocking other threads.
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</description>
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<priority>3</priority>
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<properties>
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<property name="xpath">
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<value>
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<![CDATA[
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//Type[../VariableDeclarator/VariableInitializer//AllocationExpression/ClassOrInterfaceType[@Image != 'ConcurrentHashMap']]
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/ReferenceType/ClassOrInterfaceType[@Image = 'Map']
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]]>
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</value>
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</property>
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</properties>
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<example>
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<![CDATA[
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public class ConcurrentApp {
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public void getMyInstance() {
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Map map1 = new HashMap(); // fine for single-threaded access
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Map map2 = new ConcurrentHashMap(); // preferred for use with multiple threads
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// the following case will be ignored by this rule
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Map map3 = someModule.methodThatReturnMap(); // might be OK, if the returned map is already thread-safe
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}
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}
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]]>
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</example>
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</rule>
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<rule name="UseNotifyAllInsteadOfNotify"
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language="java"
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since="3.0"
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message="Call Thread.notifyAll() rather than Thread.notify()"
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class="net.sourceforge.pmd.lang.rule.XPathRule"
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externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_multithreading.html#usenotifyallinsteadofnotify">
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<description>
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Thread.notify() awakens a thread monitoring the object. If more than one thread is monitoring, then only
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one is chosen. The thread chosen is arbitrary; thus its usually safer to call notifyAll() instead.
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</description>
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<priority>3</priority>
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<properties>
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<property name="xpath">
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<value>
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<![CDATA[
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//StatementExpression/PrimaryExpression
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[PrimarySuffix/Arguments[@ArgumentCount = '0']]
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[
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PrimaryPrefix[
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./Name[@Image='notify' or ends-with(@Image,'.notify')]
|
||
|
|
or ../PrimarySuffix/@Image='notify'
|
||
|
|
or (./AllocationExpression and ../PrimarySuffix[@Image='notify'])
|
||
|
|
]
|
||
|
|
]
|
||
|
|
]]>
|
||
|
|
</value>
|
||
|
|
</property>
|
||
|
|
</properties>
|
||
|
|
<example>
|
||
|
|
<![CDATA[
|
||
|
|
void bar() {
|
||
|
|
x.notify();
|
||
|
|
// If many threads are monitoring x, only one (and you won't know which) will be notified.
|
||
|
|
// use instead:
|
||
|
|
x.notifyAll();
|
||
|
|
}
|
||
|
|
]]>
|
||
|
|
</example>
|
||
|
|
</rule>
|
||
|
|
|
||
|
|
</ruleset>
|