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8193031: Collections.addAll is likely to perform worse than Collection.addAll #1764

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8193031: Collections.addAll is likely to perform worse than Collection.addAll #1764

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0e33c90
8193031: add elements in bulk in Collections.addAll()
stsypanov Dec 14, 2020
cb78166
8193031: add elements in bulk in Collections.addAll()
stsypanov Dec 14, 2020
81b1b1a
Merge branch 'master' into add-all
stsypanov Dec 21, 2020
7667b8a
Merge remote-tracking branch 'origin/add-all' into add-all
stsypanov Dec 21, 2020
c438d28
Merge branch 'master' into add-all
stsypanov Dec 28, 2020
ea8ea50
8193031: revert implementation change but keep one for JavaDoc
stsypanov Dec 29, 2020
9d6dcf3
Merge branch 'master' into add-all
stsypanov Dec 29, 2020
13c23c5
Merge branch 'master' into add-all
stsypanov Jan 14, 2021
096c5de
8193031: fix JavaDoc
stsypanov Jan 14, 2021
2400492
Merge branch 'master' into add-all
stsypanov Jan 14, 2021
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9 changes: 3 additions & 6 deletions src/java.base/share/classes/java/util/Collections.java
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Expand Up @@ -5563,8 +5563,7 @@ public static boolean disjoint(Collection<?> c1, Collection<?> c2) {
* Adds all of the specified elements to the specified collection.
* Elements to be added may be specified individually or as an array.
* The behavior of this convenience method is identical to that of
* {@code c.addAll(Arrays.asList(elements))}, but this method is likely
* to run significantly faster under most implementations.
* {@code c.addAll(Arrays.asList(elements))}.
*
* <p>When elements are specified individually, this method provides a
* convenient way to add a few elements to an existing collection:
Expand All @@ -5587,11 +5586,9 @@ public static boolean disjoint(Collection<?> c1, Collection<?> c2) {
* @since 1.5
*/
@SafeVarargs
@SuppressWarnings("varargs")
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I don't think you need a SuppressWarnings here

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Hi, without this I get failed build:

Compiling 3057 files for java.base
Compiling 89 properties into resource bundles for java.desktop
/home/s.tsypanov/IdeaProjects/jdk-github/src/java.base/share/classes/java/util/Collections.java:5590: warning: [varargs] Varargs method could cause heap pollution from non-reifiable varargs parameter elements
        return c.addAll(Arrays.asList(elements));
                                      ^
error: warnings found and -Werror specified
1 error
1 warning
make[3]: *** [/home/s.tsypanov/IdeaProjects/jdk-github/build/linux-x86_64-server-release/jdk/modules/java.base/_the.java.base_batch] Error 1
CompileJavaModules.gmk:604: recipe for target '/home/s.tsypanov/IdeaProjects/jdk-github/build/linux-x86_64-server-release/jdk/modules/java.base/_the.java.base_batch' failed
make[2]: *** [java.base-java] Error 2
make[2]: *** Waiting for unfinished jobs....
make/Main.gmk:193: recipe for target 'java.base-java' failed

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ok, it means there is a bug in the compiler, the analysis done for unsafe varargs (with -Xlint:varargs) doesn't check that the called method (here Arrays.asList()) is tagged with @SafeVarargs.

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Should I then wait for the fix of that bug to remove @SupressWarnings?

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I don't think so, the code is fine, for me.

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I've looked into com.sun.tools.javac.comp.Check and it seems the warning is produced here:

        @Override
        public void warn(LintCategory lint) {
            boolean warned = this.warned;
            super.warn(lint);
            if (warned) return; // suppress redundant diagnostics
            switch (lint) {
                case UNCHECKED:
                    Check.this.warnUnchecked(pos(), Warnings.ProbFoundReq(diags.fragment(uncheckedKey), found, expected));
                    break;
                case VARARGS:
                    if (method != null &&
                            method.attribute(syms.trustMeType.tsym) != null &&
                            isTrustMeAllowedOnMethod(method) &&
                            !types.isReifiable(method.type.getParameterTypes().last())) {
                        Check.this.warnUnsafeVararg(pos(), Warnings.VarargsUnsafeUseVarargsParam(method.params.last()));
                    }
                    break;
                default:
                    throw new AssertionError("Unexpected lint: " + lint);
            }
        }

Can we somehow read @SaveVarargs from signature of Arrays.asList() to avoid the warning?

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@forax I've sent a mail into compiler-dev list: http://mail.openjdk.java.net/pipermail/compiler-dev/2020-December/015857.html

Let's see what they decide.

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FYI, despite the confusing (historical) name, syms.trustMeType is the SafeVarargs annotation. See Symtab.java, line 579.

public static <T> boolean addAll(Collection<? super T> c, T... elements) {
boolean result = false;
for (T element : elements)
result |= c.add(element);
return result;
return c.addAll(Arrays.asList(elements));
}

/**
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