2018-06-16 20:39:36 +00:00
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< title > Multithreading | PMD Source Code Analyzer< / title >
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2018-07-29 10:39:27 +00:00
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2018-06-16 20:39:36 +00:00
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< h1 class = "post-title-main" > Multithreading< / h1 >
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< div class = "summary" > Rules that flag issues when dealing with multiple threads of execution.< / div >
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< a target = "_blank" href = "https://github.com/pmd/pmd/blob/master/docs/../pmd-java/src/main/resources/category/java/multithreading.xml" class = "btn btn-default githubEditButton" role = "button" > < i class = "fa fa-github fa-lg" > < / i > Edit me< / a >
< h2 id = "avoidsynchronizedatmethodlevel" > AvoidSynchronizedAtMethodLevel< / h2 >
< p > < strong > Since:< / strong > PMD 3.0< / p >
< p > < strong > Priority:< / strong > Medium (3)< / p >
< p > Method-level synchronization can cause problems when new code is added to the method.
Block-level synchronization helps to ensure that only the code that needs synchronization
gets it.< / p >
< p > < strong > This rule is defined by the following XPath expression:< / strong > < / p >
< div class = "language-xpath highlighter-rouge" > < div class = "highlight" > < pre class = "highlight" > < code > < span class = "o" > //< / span > < span class = "nt" > MethodDeclaration< / span > < span class = "p" > [< / span > < span class = "na" > @Synchronized< / span > < span class = "err" > =< / span > < span class = "s1" > 'true'< / span > < span class = "p" > ]< / span > < span class = "w" >
< / span > < / code > < / pre > < / div > < / div >
< p > < strong > Example(s):< / strong > < / p >
< div class = "language-java highlighter-rouge" > < div class = "highlight" > < pre class = "highlight" > < code > < span class = "kd" > public< / span > < span class = "kd" > class< / span > < span class = "nc" > Foo< / span > < span class = "o" > {< / span >
< span class = "c1" > // Try to avoid this:< / span >
< span class = "kd" > synchronized< / span > < span class = "kt" > void< / span > < span class = "nf" > foo< / span > < span class = "o" > ()< / span > < span class = "o" > {< / span >
< span class = "o" > }< / span >
< span class = "c1" > // Prefer this:< / span >
< span class = "kt" > void< / span > < span class = "nf" > bar< / span > < span class = "o" > ()< / span > < span class = "o" > {< / span >
< span class = "kd" > synchronized< / span > < span class = "o" > (< / span > < span class = "k" > this< / span > < span class = "o" > )< / span > < span class = "o" > {< / span >
< span class = "o" > }< / span >
< span class = "o" > }< / span >
< span class = "c1" > // Try to avoid this for static methods:< / span >
< span class = "kd" > static< / span > < span class = "kd" > synchronized< / span > < span class = "kt" > void< / span > < span class = "nf" > fooStatic< / span > < span class = "o" > ()< / span > < span class = "o" > {< / span >
< span class = "o" > }< / span >
< span class = "c1" > // Prefer this:< / span >
< span class = "kd" > static< / span > < span class = "kt" > void< / span > < span class = "nf" > barStatic< / span > < span class = "o" > ()< / span > < span class = "o" > {< / span >
< span class = "kd" > synchronized< / span > < span class = "o" > (< / span > < span class = "n" > Foo< / span > < span class = "o" > .< / span > < span class = "na" > class< / span > < span class = "o" > )< / span > < span class = "o" > {< / span >
< span class = "o" > }< / span >
< span class = "o" > }< / span >
< span class = "o" > }< / span >
< / code > < / pre > < / div > < / div >
< p > < strong > Use this rule by referencing it:< / strong > < / p >
< div class = "language-xml highlighter-rouge" > < div class = "highlight" > < pre class = "highlight" > < code > < span class = "nt" > < rule< / span > < span class = "na" > ref=< / span > < span class = "s" > "category/java/multithreading.xml/AvoidSynchronizedAtMethodLevel"< / span > < span class = "nt" > /> < / span >
< / code > < / pre > < / div > < / div >
< h2 id = "avoidthreadgroup" > AvoidThreadGroup< / h2 >
< p > < strong > Since:< / strong > PMD 3.6< / p >
< p > < strong > Priority:< / strong > Medium (3)< / p >
< p > Avoid using java.lang.ThreadGroup; although it is intended to be used in a threaded environment
it contains methods that are not thread-safe.< / p >
< p > < strong > This rule is defined by the following XPath expression:< / strong > < / p >
< div class = "language-xpath highlighter-rouge" > < div class = "highlight" > < pre class = "highlight" > < code > < span class = "o" > //< / span > < span class = "nt" > AllocationExpression< / span > < span class = "o" > /< / span > < span class = "nt" > ClassOrInterfaceType< / span > < span class = "p" > [< / span > < span class = "nn" > pmd-java:< / span > < span class = "nf" > typeIs< / span > < span class = "p" > (< / span > < span class = "s1" > 'java.lang.ThreadGroup'< / span > < span class = "p" > )]|< / span > < span class = "w" >
< / span > < span class = "o" > //< / span > < span class = "nt" > PrimarySuffix< / span > < span class = "p" > [< / span > < span class = "nf" > contains< / span > < span class = "p" > (< / span > < span class = "na" > @Image< / span > < span class = "p" > ,< / span > < span class = "w" > < / span > < span class = "s1" > 'getThreadGroup'< / span > < span class = "p" > )]< / span > < span class = "w" >
< / span > < / code > < / pre > < / div > < / div >
< p > < strong > Example(s):< / strong > < / p >
< div class = "language-java highlighter-rouge" > < div class = "highlight" > < pre class = "highlight" > < code > < span class = "kd" > public< / span > < span class = "kd" > class< / span > < span class = "nc" > Bar< / span > < span class = "o" > {< / span >
< span class = "kt" > void< / span > < span class = "nf" > buz< / span > < span class = "o" > ()< / span > < span class = "o" > {< / span >
< span class = "n" > ThreadGroup< / span > < span class = "n" > tg< / span > < span class = "o" > =< / span > < span class = "k" > new< / span > < span class = "n" > ThreadGroup< / span > < span class = "o" > (< / span > < span class = "s" > "My threadgroup"< / span > < span class = "o" > );< / span >
< span class = "n" > tg< / span > < span class = "o" > =< / span > < span class = "k" > new< / span > < span class = "n" > ThreadGroup< / span > < span class = "o" > (< / span > < span class = "n" > tg< / span > < span class = "o" > ,< / span > < span class = "s" > "my thread group"< / span > < span class = "o" > );< / span >
< span class = "n" > tg< / span > < span class = "o" > =< / span > < span class = "n" > Thread< / span > < span class = "o" > .< / span > < span class = "na" > currentThread< / span > < span class = "o" > ().< / span > < span class = "na" > getThreadGroup< / span > < span class = "o" > ();< / span >
< span class = "n" > tg< / span > < span class = "o" > =< / span > < span class = "n" > System< / span > < span class = "o" > .< / span > < span class = "na" > getSecurityManager< / span > < span class = "o" > ().< / span > < span class = "na" > getThreadGroup< / span > < span class = "o" > ();< / span >
< span class = "o" > }< / span >
< span class = "o" > }< / span >
< / code > < / pre > < / div > < / div >
< p > < strong > Use this rule by referencing it:< / strong > < / p >
< div class = "language-xml highlighter-rouge" > < div class = "highlight" > < pre class = "highlight" > < code > < span class = "nt" > < rule< / span > < span class = "na" > ref=< / span > < span class = "s" > "category/java/multithreading.xml/AvoidThreadGroup"< / span > < span class = "nt" > /> < / span >
< / code > < / pre > < / div > < / div >
< h2 id = "avoidusingvolatile" > AvoidUsingVolatile< / h2 >
< p > < strong > Since:< / strong > PMD 4.1< / p >
< p > < strong > Priority:< / strong > Medium High (2)< / p >
< p > Use of the keyword ‘ ’
a good expertise of the Java Memory Model. Moreover, its range of action is somewhat misknown. Therefore,
the volatile keyword should not be used for maintenance purpose and portability.< / p >
< p > < strong > This rule is defined by the following XPath expression:< / strong > < / p >
< div class = "language-xpath highlighter-rouge" > < div class = "highlight" > < pre class = "highlight" > < code > < span class = "o" > //< / span > < span class = "nt" > FieldDeclaration< / span > < span class = "p" > [< / span > < span class = "nf" > contains< / span > < span class = "p" > (< / span > < span class = "na" > @Volatile< / span > < span class = "p" > ,< / span > < span class = "s1" > 'true'< / span > < span class = "p" > )]< / span > < span class = "w" >
< / span > < / code > < / pre > < / div > < / div >
< p > < strong > Example(s):< / strong > < / p >
< div class = "language-java highlighter-rouge" > < div class = "highlight" > < pre class = "highlight" > < code > < span class = "kd" > public< / span > < span class = "kd" > class< / span > < span class = "nc" > ThrDeux< / span > < span class = "o" > {< / span >
< span class = "kd" > private< / span > < span class = "kd" > volatile< / span > < span class = "n" > String< / span > < span class = "n" > var1< / span > < span class = "o" > ;< / span > < span class = "c1" > // not suggested< / span >
< span class = "kd" > private< / span > < span class = "n" > String< / span > < span class = "n" > var2< / span > < span class = "o" > ;< / span > < span class = "c1" > // preferred< / span >
< span class = "o" > }< / span >
< / code > < / pre > < / div > < / div >
< p > < strong > Use this rule by referencing it:< / strong > < / p >
< div class = "language-xml highlighter-rouge" > < div class = "highlight" > < pre class = "highlight" > < code > < span class = "nt" > < rule< / span > < span class = "na" > ref=< / span > < span class = "s" > "category/java/multithreading.xml/AvoidUsingVolatile"< / span > < span class = "nt" > /> < / span >
< / code > < / pre > < / div > < / div >
< h2 id = "donotusethreads" > DoNotUseThreads< / h2 >
< p > < strong > Since:< / strong > PMD 4.1< / p >
< p > < strong > Priority:< / strong > Medium (3)< / p >
< p > The J2EE specification explicitly forbids the use of threads.< / p >
< p > < strong > This rule is defined by the following XPath expression:< / strong > < / p >
< div class = "language-xpath highlighter-rouge" > < div class = "highlight" > < pre class = "highlight" > < code > < span class = "o" > //< / span > < span class = "nt" > ClassOrInterfaceType< / span > < span class = "p" > [< / span > < span class = "na" > @Image< / span > < span class = "w" > < / span > < span class = "err" > =< / span > < span class = "w" > < / span > < span class = "s1" > 'Thread'< / span > < span class = "w" > < / span > < span class = "ow" > or< / span > < span class = "w" > < / span > < span class = "na" > @Image< / span > < span class = "w" > < / span > < span class = "err" > =< / span > < span class = "w" > < / span > < span class = "s1" > 'Runnable'< / span > < span class = "p" > ]< / span > < span class = "w" >
< / span > < / code > < / pre > < / div > < / div >
< p > < strong > Example(s):< / strong > < / p >
< div class = "language-java highlighter-rouge" > < div class = "highlight" > < pre class = "highlight" > < code > < span class = "c1" > // This is not allowed< / span >
< span class = "kd" > public< / span > < span class = "kd" > class< / span > < span class = "nc" > UsingThread< / span > < span class = "kd" > extends< / span > < span class = "n" > Thread< / span > < span class = "o" > {< / span >
< span class = "o" > }< / span >
< span class = "c1" > // Neither this,< / span >
< span class = "kd" > public< / span > < span class = "kd" > class< / span > < span class = "nc" > OtherThread< / span > < span class = "kd" > implements< / span > < span class = "n" > Runnable< / span > < span class = "o" > {< / span >
< span class = "c1" > // Nor this ...< / span >
< span class = "kd" > public< / span > < span class = "kt" > void< / span > < span class = "nf" > methode< / span > < span class = "o" > ()< / span > < span class = "o" > {< / span >
< span class = "n" > Runnable< / span > < span class = "n" > thread< / span > < span class = "o" > =< / span > < span class = "k" > new< / span > < span class = "n" > Thread< / span > < span class = "o" > ();< / span > < span class = "n" > thread< / span > < span class = "o" > .< / span > < span class = "na" > run< / span > < span class = "o" > ();< / span >
< span class = "o" > }< / span >
< span class = "o" > }< / span >
< / code > < / pre > < / div > < / div >
< p > < strong > Use this rule by referencing it:< / strong > < / p >
< div class = "language-xml highlighter-rouge" > < div class = "highlight" > < pre class = "highlight" > < code > < span class = "nt" > < rule< / span > < span class = "na" > ref=< / span > < span class = "s" > "category/java/multithreading.xml/DoNotUseThreads"< / span > < span class = "nt" > /> < / span >
< / code > < / pre > < / div > < / div >
< h2 id = "dontcallthreadrun" > DontCallThreadRun< / h2 >
< p > < strong > Since:< / strong > PMD 4.3< / p >
< p > < strong > Priority:< / strong > Medium Low (4)< / p >
< p > Explicitly calling Thread.run() method will execute in the caller’ < / p >
< p > < strong > This rule is defined by the following XPath expression:< / strong > < / p >
< div class = "language-xpath highlighter-rouge" > < div class = "highlight" > < pre class = "highlight" > < code > < span class = "o" > //< / span > < span class = "nt" > StatementExpression< / span > < span class = "o" > /< / span > < span class = "nt" > PrimaryExpression< / span > < span class = "w" >
< / span > < span class = "p" > [< / span > < span class = "w" >
< / span > < span class = "nt" > PrimaryPrefix< / span > < span class = "w" >
< / span > < span class = "p" > [< / span > < span class = "w" >
< / span > < span class = "p" > .< / span > < span class = "o" > /< / span > < span class = "nt" > Name< / span > < span class = "p" > [< / span > < span class = "nf" > ends-with< / span > < span class = "p" > (< / span > < span class = "na" > @Image< / span > < span class = "p" > ,< / span > < span class = "w" > < / span > < span class = "s1" > '.run'< / span > < span class = "p" > )< / span > < span class = "w" > < / span > < span class = "ow" > or< / span > < span class = "w" > < / span > < span class = "na" > @Image< / span > < span class = "w" > < / span > < span class = "err" > =< / span > < span class = "w" > < / span > < span class = "s1" > 'run'< / span > < span class = "p" > ]< / span > < span class = "w" >
< / span > < span class = "ow" > and< / span > < span class = "w" > < / span > < span class = "nf" > substring-before< / span > < span class = "p" > (< / span > < span class = "nt" > Name< / span > < span class = "err" > /< / span > < span class = "na" > @Image< / span > < span class = "p" > ,< / span > < span class = "w" > < / span > < span class = "s1" > '.'< / span > < span class = "p" > )< / span > < span class = "w" > < / span > < span class = "err" > =< / span > < span class = "o" > //< / span > < span class = "nt" > VariableDeclarator< / span > < span class = "o" > /< / span > < span class = "nt" > VariableDeclaratorId< / span > < span class = "err" > /< / span > < span class = "na" > @Image< / span > < span class = "w" >
< / span > < span class = "p" > [..< / span > < span class = "err" > /< / span > < span class = "p" > ..< / span > < span class = "err" > /< / span > < span class = "p" > ..< / span > < span class = "o" > /< / span > < span class = "nt" > Type< / span > < span class = "o" > /< / span > < span class = "nt" > ReferenceType< / span > < span class = "o" > /< / span > < span class = "nt" > ClassOrInterfaceType< / span > < span class = "p" > [< / span > < span class = "nf" > typeIs< / span > < span class = "p" > (< / span > < span class = "s1" > 'java.lang.Thread'< / span > < span class = "p" > )]]< / span > < span class = "w" >
< / span > < span class = "ow" > or< / span > < span class = "w" > < / span > < span class = "p" > (.< / span > < span class = "o" > /< / span > < span class = "nt" > AllocationExpression< / span > < span class = "o" > /< / span > < span class = "nt" > ClassOrInterfaceType< / span > < span class = "p" > [< / span > < span class = "nf" > typeIs< / span > < span class = "p" > (< / span > < span class = "s1" > 'java.lang.Thread'< / span > < span class = "p" > )]< / span > < span class = "w" >
< / span > < span class = "ow" > and< / span > < span class = "w" > < / span > < span class = "p" > ..< / span > < span class = "o" > /< / span > < span class = "nt" > PrimarySuffix< / span > < span class = "p" > [< / span > < span class = "na" > @Image< / span > < span class = "w" > < / span > < span class = "err" > =< / span > < span class = "w" > < / span > < span class = "s1" > 'run'< / span > < span class = "p" > ])< / span > < span class = "w" >
< / span > < span class = "p" > ]< / span > < span class = "w" >
< / span > < span class = "p" > ]< / span > < span class = "w" >
< / span > < / code > < / pre > < / div > < / div >
< p > < strong > Example(s):< / strong > < / p >
< div class = "language-java highlighter-rouge" > < div class = "highlight" > < pre class = "highlight" > < code > < span class = "n" > Thread< / span > < span class = "n" > t< / span > < span class = "o" > =< / span > < span class = "k" > new< / span > < span class = "n" > Thread< / span > < span class = "o" > ();< / span >
< span class = "n" > t< / span > < span class = "o" > .< / span > < span class = "na" > run< / span > < span class = "o" > ();< / span > < span class = "c1" > // use t.start() instead< / span >
< span class = "k" > new< / span > < span class = "nf" > Thread< / span > < span class = "o" > ().< / span > < span class = "na" > run< / span > < span class = "o" > ();< / span > < span class = "c1" > // same violation< / span >
< / code > < / pre > < / div > < / div >
< p > < strong > Use this rule by referencing it:< / strong > < / p >
< div class = "language-xml highlighter-rouge" > < div class = "highlight" > < pre class = "highlight" > < code > < span class = "nt" > < rule< / span > < span class = "na" > ref=< / span > < span class = "s" > "category/java/multithreading.xml/DontCallThreadRun"< / span > < span class = "nt" > /> < / span >
< / code > < / pre > < / div > < / div >
< h2 id = "doublecheckedlocking" > DoubleCheckedLocking< / h2 >
< p > < strong > Since:< / strong > PMD 1.04< / p >
< p > < strong > Priority:< / strong > High (1)< / p >
< p > Partially created objects can be returned by the Double Checked Locking pattern when used in Java.
An optimizing JRE may assign a reference to the baz variable before it calls the constructor of the object the
reference points to.< / p >
< p > Note: With Java 5, you can make Double checked locking work, if you declare the variable to be < code class = "highlighter-rouge" > volatile< / code > .< / p >
< p > For more details refer to: < a href = "http://www.javaworld.com/javaworld/jw-02-2001/jw-0209-double.html" > http://www.javaworld.com/javaworld/jw-02-2001/jw-0209-double.html< / a >
or < a href = "http://www.cs.umd.edu/~pugh/java/memoryModel/DoubleCheckedLocking.html" > http://www.cs.umd.edu/~pugh/java/memoryModel/DoubleCheckedLocking.html< / a > < / p >
< p > < strong > This rule is defined by the following Java class:< / strong > < a href = "https://github.com/pmd/pmd/blob/master/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/rule/multithreading/DoubleCheckedLockingRule.java" > net.sourceforge.pmd.lang.java.rule.multithreading.DoubleCheckedLockingRule< / a > < / p >
< p > < strong > Example(s):< / strong > < / p >
< div class = "language-java highlighter-rouge" > < div class = "highlight" > < pre class = "highlight" > < code > < span class = "kd" > public< / span > < span class = "kd" > class< / span > < span class = "nc" > Foo< / span > < span class = "o" > {< / span >
< span class = "cm" > /*volatile */< / span > < span class = "n" > Object< / span > < span class = "n" > baz< / span > < span class = "o" > =< / span > < span class = "kc" > null< / span > < span class = "o" > ;< / span > < span class = "c1" > // fix for Java5 and later: volatile< / span >
< span class = "n" > Object< / span > < span class = "nf" > bar< / span > < span class = "o" > ()< / span > < span class = "o" > {< / span >
< span class = "k" > if< / span > < span class = "o" > (< / span > < span class = "n" > baz< / span > < span class = "o" > ==< / span > < span class = "kc" > null< / span > < span class = "o" > )< / span > < span class = "o" > {< / span > < span class = "c1" > // baz may be non-null yet not fully created< / span >
< span class = "kd" > synchronized< / span > < span class = "o" > (< / span > < span class = "k" > this< / span > < span class = "o" > )< / span > < span class = "o" > {< / span >
< span class = "k" > if< / span > < span class = "o" > (< / span > < span class = "n" > baz< / span > < span class = "o" > ==< / span > < span class = "kc" > null< / span > < span class = "o" > )< / span > < span class = "o" > {< / span >
< span class = "n" > baz< / span > < span class = "o" > =< / span > < span class = "k" > new< / span > < span class = "n" > Object< / span > < span class = "o" > ();< / span >
< span class = "o" > }< / span >
< span class = "o" > }< / span >
< span class = "o" > }< / span >
< span class = "k" > return< / span > < span class = "n" > baz< / span > < span class = "o" > ;< / span >
< span class = "o" > }< / span >
< span class = "o" > }< / span >
< / code > < / pre > < / div > < / div >
< p > < strong > Use this rule by referencing it:< / strong > < / p >
< div class = "language-xml highlighter-rouge" > < div class = "highlight" > < pre class = "highlight" > < code > < span class = "nt" > < rule< / span > < span class = "na" > ref=< / span > < span class = "s" > "category/java/multithreading.xml/DoubleCheckedLocking"< / span > < span class = "nt" > /> < / span >
< / code > < / pre > < / div > < / div >
< h2 id = "nonthreadsafesingleton" > NonThreadSafeSingleton< / h2 >
< p > < strong > Since:< / strong > PMD 3.4< / p >
< p > < strong > Priority:< / strong > Medium (3)< / p >
< p > Non-thread safe singletons can result in bad state changes. Eliminate
static singletons if possible by instantiating the object directly. Static
singletons are usually not needed as only a single instance exists anyway.
Other possible fixes are to synchronize the entire method or to use an
< a href = "https://en.wikipedia.org/wiki/Initialization-on-demand_holder_idiom" > initialize-on-demand holder class< / a > .< / p >
< p > Refrain from using the double-checked locking pattern. The Java Memory Model doesn’
guarantee it to work unless the variable is declared as < code class = "highlighter-rouge" > volatile< / code > , adding an uneeded
performance penalty. < a href = "http://www.cs.umd.edu/~pugh/java/memoryModel/DoubleCheckedLocking.html" > Reference< / a > < / p >
< p > See Effective Java, item 48.< / p >
< p > < strong > This rule is defined by the following Java class:< / strong > < a href = "https://github.com/pmd/pmd/blob/master/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/rule/multithreading/NonThreadSafeSingletonRule.java" > net.sourceforge.pmd.lang.java.rule.multithreading.NonThreadSafeSingletonRule< / a > < / p >
< p > < strong > Example(s):< / strong > < / p >
< div class = "language-java highlighter-rouge" > < div class = "highlight" > < pre class = "highlight" > < code > < span class = "kd" > private< / span > < span class = "kd" > static< / span > < span class = "n" > Foo< / span > < span class = "n" > foo< / span > < span class = "o" > =< / span > < span class = "kc" > null< / span > < span class = "o" > ;< / span >
< span class = "c1" > //multiple simultaneous callers may see partially initialized objects< / span >
< span class = "kd" > public< / span > < span class = "kd" > static< / span > < span class = "n" > Foo< / span > < span class = "nf" > getFoo< / span > < span class = "o" > ()< / span > < span class = "o" > {< / span >
< span class = "k" > if< / span > < span class = "o" > (< / span > < span class = "n" > foo< / span > < span class = "o" > ==< / span > < span class = "kc" > null< / span > < span class = "o" > )< / span > < span class = "o" > {< / span >
< span class = "n" > foo< / span > < span class = "o" > =< / span > < span class = "k" > new< / span > < span class = "n" > Foo< / span > < span class = "o" > ();< / span >
< span class = "o" > }< / span >
< span class = "k" > return< / span > < span class = "n" > foo< / span > < span class = "o" > ;< / span >
< span class = "o" > }< / span >
< / code > < / pre > < / div > < / div >
< p > < strong > This rule has the following properties:< / strong > < / p >
< table >
< thead >
< tr >
< th > Name< / th >
< th > Default Value< / th >
< th > Description< / th >
< th > Multivalued< / th >
< / tr >
< / thead >
< tbody >
< tr >
< td > checkNonStaticFields< / td >
< td > false< / td >
< td > Check for non-static fields. Do not set this to true and checkNonStaticMethods to false.< / td >
< td > no< / td >
< / tr >
< tr >
< td > checkNonStaticMethods< / td >
< td > true< / td >
< td > Check for non-static methods. Do not set this to false and checkNonStaticFields to true.< / td >
< td > no< / td >
< / tr >
< / tbody >
< / table >
< p > < strong > Use this rule by referencing it:< / strong > < / p >
< div class = "language-xml highlighter-rouge" > < div class = "highlight" > < pre class = "highlight" > < code > < span class = "nt" > < rule< / span > < span class = "na" > ref=< / span > < span class = "s" > "category/java/multithreading.xml/NonThreadSafeSingleton"< / span > < span class = "nt" > /> < / span >
< / code > < / pre > < / div > < / div >
< h2 id = "unsynchronizedstaticdateformatter" > UnsynchronizedStaticDateFormatter< / h2 >
< p > < strong > Since:< / strong > PMD 3.6< / p >
< p > < strong > Priority:< / strong > Medium (3)< / p >
< p > SimpleDateFormat instances are not synchronized. Sun recommends using separate format instances
for each thread. If multiple threads must access a static formatter, the formatter must be
synchronized either on method or block level.< / p >
< p > < strong > This rule is defined by the following Java class:< / strong > < a href = "https://github.com/pmd/pmd/blob/master/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/rule/multithreading/UnsynchronizedStaticDateFormatterRule.java" > net.sourceforge.pmd.lang.java.rule.multithreading.UnsynchronizedStaticDateFormatterRule< / a > < / p >
< p > < strong > Example(s):< / strong > < / p >
< div class = "language-java highlighter-rouge" > < div class = "highlight" > < pre class = "highlight" > < code > < span class = "kd" > public< / span > < span class = "kd" > class< / span > < span class = "nc" > Foo< / span > < span class = "o" > {< / span >
< span class = "kd" > private< / span > < span class = "kd" > static< / span > < span class = "kd" > final< / span > < span class = "n" > SimpleDateFormat< / span > < span class = "n" > sdf< / span > < span class = "o" > =< / span > < span class = "k" > new< / span > < span class = "n" > SimpleDateFormat< / span > < span class = "o" > ();< / span >
< span class = "kt" > void< / span > < span class = "nf" > bar< / span > < span class = "o" > ()< / span > < span class = "o" > {< / span >
< span class = "n" > sdf< / span > < span class = "o" > .< / span > < span class = "na" > format< / span > < span class = "o" > ();< / span > < span class = "c1" > // poor, no thread-safety< / span >
< span class = "o" > }< / span >
< span class = "kd" > synchronized< / span > < span class = "kt" > void< / span > < span class = "nf" > foo< / span > < span class = "o" > ()< / span > < span class = "o" > {< / span >
< span class = "n" > sdf< / span > < span class = "o" > .< / span > < span class = "na" > format< / span > < span class = "o" > ();< / span > < span class = "c1" > // preferred< / span >
< span class = "o" > }< / span >
< span class = "o" > }< / span >
< / code > < / pre > < / div > < / div >
< p > < strong > Use this rule by referencing it:< / strong > < / p >
< div class = "language-xml highlighter-rouge" > < div class = "highlight" > < pre class = "highlight" > < code > < span class = "nt" > < rule< / span > < span class = "na" > ref=< / span > < span class = "s" > "category/java/multithreading.xml/UnsynchronizedStaticDateFormatter"< / span > < span class = "nt" > /> < / span >
< / code > < / pre > < / div > < / div >
< h2 id = "useconcurrenthashmap" > UseConcurrentHashMap< / h2 >
< p > < strong > Since:< / strong > PMD 4.2.6< / p >
< p > < strong > Priority:< / strong > Medium (3)< / p >
< p > < strong > Minimum Language Version:< / strong > Java 1.5< / p >
< p > Since Java5 brought a new implementation of the Map designed for multi-threaded access, you can
perform efficient map reads without blocking other threads.< / p >
< p > < strong > This rule is defined by the following XPath expression:< / strong > < / p >
< div class = "language-xpath highlighter-rouge" > < div class = "highlight" > < pre class = "highlight" > < code > < span class = "o" > //< / span > < span class = "nt" > Type< / span > < span class = "p" > [..< / span > < span class = "o" > /< / span > < span class = "nt" > VariableDeclarator< / span > < span class = "o" > /< / span > < span class = "nt" > VariableInitializer< / span > < span class = "o" > //< / span > < span class = "nt" > AllocationExpression< / span > < span class = "o" > /< / span > < span class = "nt" > ClassOrInterfaceType< / span > < span class = "p" > [< / span > < span class = "na" > @Image< / span > < span class = "w" > < / span > < span class = "p" > !< / span > < span class = "err" > =< / span > < span class = "w" > < / span > < span class = "s1" > 'ConcurrentHashMap'< / span > < span class = "p" > ]]< / span > < span class = "w" >
< / span > < span class = "o" > /< / span > < span class = "nt" > ReferenceType< / span > < span class = "o" > /< / span > < span class = "nt" > ClassOrInterfaceType< / span > < span class = "p" > [< / span > < span class = "na" > @Image< / span > < span class = "w" > < / span > < span class = "err" > =< / span > < span class = "w" > < / span > < span class = "s1" > 'Map'< / span > < span class = "p" > ]< / span > < span class = "w" >
< / span > < / code > < / pre > < / div > < / div >
< p > < strong > Example(s):< / strong > < / p >
< div class = "language-java highlighter-rouge" > < div class = "highlight" > < pre class = "highlight" > < code > < span class = "kd" > public< / span > < span class = "kd" > class< / span > < span class = "nc" > ConcurrentApp< / span > < span class = "o" > {< / span >
< span class = "kd" > public< / span > < span class = "kt" > void< / span > < span class = "nf" > getMyInstance< / span > < span class = "o" > ()< / span > < span class = "o" > {< / span >
< span class = "n" > Map< / span > < span class = "n" > map1< / span > < span class = "o" > =< / span > < span class = "k" > new< / span > < span class = "n" > HashMap< / span > < span class = "o" > ();< / span > < span class = "c1" > // fine for single-threaded access< / span >
< span class = "n" > Map< / span > < span class = "n" > map2< / span > < span class = "o" > =< / span > < span class = "k" > new< / span > < span class = "n" > ConcurrentHashMap< / span > < span class = "o" > ();< / span > < span class = "c1" > // preferred for use with multiple threads< / span >
< span class = "c1" > // the following case will be ignored by this rule< / span >
< span class = "n" > Map< / span > < span class = "n" > map3< / span > < span class = "o" > =< / span > < span class = "n" > someModule< / span > < span class = "o" > .< / span > < span class = "na" > methodThatReturnMap< / span > < span class = "o" > ();< / span > < span class = "c1" > // might be OK, if the returned map is already thread-safe< / span >
< span class = "o" > }< / span >
< span class = "o" > }< / span >
< / code > < / pre > < / div > < / div >
< p > < strong > Use this rule by referencing it:< / strong > < / p >
< div class = "language-xml highlighter-rouge" > < div class = "highlight" > < pre class = "highlight" > < code > < span class = "nt" > < rule< / span > < span class = "na" > ref=< / span > < span class = "s" > "category/java/multithreading.xml/UseConcurrentHashMap"< / span > < span class = "nt" > /> < / span >
< / code > < / pre > < / div > < / div >
< h2 id = "usenotifyallinsteadofnotify" > UseNotifyAllInsteadOfNotify< / h2 >
< p > < strong > Since:< / strong > PMD 3.0< / p >
< p > < strong > Priority:< / strong > Medium (3)< / p >
< p > Thread.notify() awakens a thread monitoring the object. If more than one thread is monitoring, then only
one is chosen. The thread chosen is arbitrary; thus its usually safer to call notifyAll() instead.< / p >
< p > < strong > This rule is defined by the following XPath expression:< / strong > < / p >
< div class = "language-xpath highlighter-rouge" > < div class = "highlight" > < pre class = "highlight" > < code > < span class = "o" > //< / span > < span class = "nt" > StatementExpression< / span > < span class = "o" > /< / span > < span class = "nt" > PrimaryExpression< / span > < span class = "w" >
< / span > < span class = "p" > [< / span > < span class = "nt" > PrimarySuffix< / span > < span class = "o" > /< / span > < span class = "nt" > Arguments< / span > < span class = "p" > [< / span > < span class = "na" > @ArgumentCount< / span > < span class = "w" > < / span > < span class = "err" > =< / span > < span class = "w" > < / span > < span class = "s1" > '0'< / span > < span class = "p" > ]]< / span > < span class = "w" >
< / span > < span class = "p" > [< / span > < span class = "w" >
< / span > < span class = "nt" > PrimaryPrefix< / span > < span class = "p" > [< / span > < span class = "w" >
< / span > < span class = "p" > .< / span > < span class = "o" > /< / span > < span class = "nt" > Name< / span > < span class = "p" > [< / span > < span class = "na" > @Image< / span > < span class = "err" > =< / span > < span class = "s1" > 'notify'< / span > < span class = "w" > < / span > < span class = "ow" > or< / span > < span class = "w" > < / span > < span class = "nf" > ends-with< / span > < span class = "p" > (< / span > < span class = "na" > @Image< / span > < span class = "p" > ,< / span > < span class = "s1" > '.notify'< / span > < span class = "p" > )]< / span > < span class = "w" >
< / span > < span class = "ow" > or< / span > < span class = "w" > < / span > < span class = "p" > ..< / span > < span class = "o" > /< / span > < span class = "nt" > PrimarySuffix< / span > < span class = "err" > /< / span > < span class = "na" > @Image< / span > < span class = "err" > =< / span > < span class = "s1" > 'notify'< / span > < span class = "w" >
< / span > < span class = "ow" > or< / span > < span class = "w" > < / span > < span class = "p" > (.< / span > < span class = "o" > /< / span > < span class = "nt" > AllocationExpression< / span > < span class = "w" > < / span > < span class = "ow" > and< / span > < span class = "w" > < / span > < span class = "p" > ..< / span > < span class = "o" > /< / span > < span class = "nt" > PrimarySuffix< / span > < span class = "p" > [< / span > < span class = "na" > @Image< / span > < span class = "err" > =< / span > < span class = "s1" > 'notify'< / span > < span class = "p" > ])< / span > < span class = "w" >
< / span > < span class = "p" > ]< / span > < span class = "w" >
< / span > < span class = "p" > ]< / span > < span class = "w" >
< / span > < / code > < / pre > < / div > < / div >
< p > < strong > Example(s):< / strong > < / p >
< div class = "language-java highlighter-rouge" > < div class = "highlight" > < pre class = "highlight" > < code > < span class = "kt" > void< / span > < span class = "nf" > bar< / span > < span class = "o" > ()< / span > < span class = "o" > {< / span >
< span class = "n" > x< / span > < span class = "o" > .< / span > < span class = "na" > notify< / span > < span class = "o" > ();< / span >
< span class = "c1" > // If many threads are monitoring x, only one (and you won't know which) will be notified.< / span >
< span class = "c1" > // use instead:< / span >
< span class = "n" > x< / span > < span class = "o" > .< / span > < span class = "na" > notifyAll< / span > < span class = "o" > ();< / span >
< span class = "o" > }< / span >
< / code > < / pre > < / div > < / div >
< p > < strong > Use this rule by referencing it:< / strong > < / p >
< div class = "language-xml highlighter-rouge" > < div class = "highlight" > < pre class = "highlight" > < code > < span class = "nt" > < rule< / span > < span class = "na" > ref=< / span > < span class = "s" > "category/java/multithreading.xml/UseNotifyAllInsteadOfNotify"< / span > < span class = "nt" > /> < / span >
< / code > < / pre > < / div > < / div >
< div class = "tags" >
< / div >
< / div >
< hr class = "shaded" / >
< footer >
< div class = "row" >
< div class = "col-lg-12 footer" >
© 2018 PMD Open Source Project. All rights reserved. < br / >
2018-07-30 03:18:24 +00:00
Site last generated: Jul 30, 2018 < br / >
2018-06-16 20:39:36 +00:00
< p > < img src = "images/pmd-logo-small.png" alt = "Company logo" / > < / p >
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< / div >
< / footer >
< / div >
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