Mixing
Conditionally remove elements from a ConcurrentHashMap (thread-safe)
I have a ConcurrentHashMap<String, Instant> which is accessed concurrently. I'd say that
map.entrySet().removeIf(e -> e.getValue().isBefore(Instant.now()));
would be a thread-safe implementation as it would never remove a String which got a new Instant by another thread right after the predicate evaluation and before the actual removal. Even if multiple threads put strings with instants into this map, never an entry with an instant after Instant.now() is removed. That's because
entrySet()is a view on the original map
removeIf()uses the iterator from theentrySet()supportingIterator.remove()
removeIf()removes theString/Instantentry by callingremove(Object, Object)
I'm just not entirely sure about (3). Who can help me out?
java multithreading
asked Nov 21 '18 at 17:17
steffensteffen
9,37022355
add a comment |
I have a ConcurrentHashMap<String, Instant> which is accessed concurrently. I'd say that
map.entrySet().removeIf(e -> e.getValue().isBefore(Instant.now()));
would be a thread-safe implementation as it would never remove a String which got a new Instant by another thread right after the predicate evaluation and before the actual removal. Even if multiple threads put strings with instants into this map, never an entry with an instant after Instant.now() is removed. That's because
entrySet()is a view on the original map
removeIf()uses the iterator from theentrySet()supportingIterator.remove()
removeIf()removes theString/Instantentry by callingremove(Object, Object)
I'm just not entirely sure about (3). Who can help me out?
java multithreading
asked Nov 21 '18 at 17:17
steffensteffen
9,37022355
Note:Instant.now()can return a different value every time it is called. This means it doesn't remove up to the same point for all entries.
– Peter Lawrey
Nov 21 '18 at 19:06
add a comment |
I have a ConcurrentHashMap<String, Instant> which is accessed concurrently. I'd say that
map.entrySet().removeIf(e -> e.getValue().isBefore(Instant.now()));
would be a thread-safe implementation as it would never remove a String which got a new Instant by another thread right after the predicate evaluation and before the actual removal. Even if multiple threads put strings with instants into this map, never an entry with an instant after Instant.now() is removed. That's because
entrySet()is a view on the original map
removeIf()uses the iterator from theentrySet()supportingIterator.remove()
removeIf()removes theString/Instantentry by callingremove(Object, Object)
I'm just not entirely sure about (3). Who can help me out?
java multithreading
asked Nov 21 '18 at 17:17
steffensteffen
9,37022355
I have a ConcurrentHashMap<String, Instant> which is accessed concurrently. I'd say that
map.entrySet().removeIf(e -> e.getValue().isBefore(Instant.now()));
would be a thread-safe implementation as it would never remove a String which got a new Instant by another thread right after the predicate evaluation and before the actual removal. Even if multiple threads put strings with instants into this map, never an entry with an instant after Instant.now() is removed. That's because
entrySet()is a view on the original map
removeIf()uses the iterator from theentrySet()supportingIterator.remove()
removeIf()removes theString/Instantentry by callingremove(Object, Object)
I'm just not entirely sure about (3). Who can help me out?
java multithreading
java multithreading
asked Nov 21 '18 at 17:17
steffensteffen
9,37022355
asked Nov 21 '18 at 17:17
steffensteffen
9,37022355
asked Nov 21 '18 at 17:17
steffensteffen
9,37022355
asked Nov 21 '18 at 17:17
steffensteffen
9,37022355
asked Nov 21 '18 at 17:17
steffensteffen
9,37022355
9,37022355
Note:Instant.now()can return a different value every time it is called. This means it doesn't remove up to the same point for all entries.
– Peter Lawrey
Nov 21 '18 at 19:06
add a comment |
Note:Instant.now()can return a different value every time it is called. This means it doesn't remove up to the same point for all entries.
– Peter Lawrey
Nov 21 '18 at 19:06
Note:
Instant.now() can return a different value every time it is called. This means it doesn't remove up to the same point for all entries.– Peter Lawrey
Nov 21 '18 at 19:06
Note:
Instant.now() can return a different value every time it is called. This means it doesn't remove up to the same point for all entries.– Peter Lawrey
Nov 21 '18 at 19:06
add a comment |
0
active
oldest
votes
Your Answer
StackExchange.ifUsing("editor", function () {
StackExchange.using("externalEditor", function () {
StackExchange.using("snippets", function () {
StackExchange.snippets.init();
});
});
}, "code-snippets");
StackExchange.ready(function() {
var channelOptions = {
tags: "".split(" "),
id: "1"
};
initTagRenderer("".split(" "), "".split(" "), channelOptions);
StackExchange.using("externalEditor", function() {
// Have to fire editor after snippets, if snippets enabled
if (StackExchange.settings.snippets.snippetsEnabled) {
StackExchange.using("snippets", function() {
createEditor();
});
}
else {
createEditor();
}
});
function createEditor() {
StackExchange.prepareEditor({
heartbeatType: 'answer',
autoActivateHeartbeat: false,
convertImagesToLinks: true,
noModals: true,
showLowRepImageUploadWarning: true,
reputationToPostImages: 10,
bindNavPrevention: true,
postfix: "",
imageUploader: {
brandingHtml: "Powered by u003ca class="icon-imgur-white" href="https://imgur.com/"u003eu003c/au003e",
contentPolicyHtml: "User contributions licensed under u003ca href="https://creativecommons.org/licenses/by-sa/3.0/"u003ecc by-sa 3.0 with attribution requiredu003c/au003e u003ca href="https://stackoverflow.com/legal/content-policy"u003e(content policy)u003c/au003e",
allowUrls: true
},
onDemand: true,
discardSelector: ".discard-answer"
,immediatelyShowMarkdownHelp:true
});
}
});
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
StackExchange.ready(
function () {
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fstackoverflow.com%2fquestions%2f53417422%2fconditionally-remove-elements-from-a-concurrenthashmap-thread-safe%23new-answer', 'question_page');
}
);
Post as a guest
Required, but never shown
0
active
oldest
votes
0
active
oldest
votes
active
oldest
votes
active
oldest
votes
Thanks for contributing an answer to Stack Overflow!
- Please be sure to answer the question. Provide details and share your research!
But avoid …
- Asking for help, clarification, or responding to other answers.
- Making statements based on opinion; back them up with references or personal experience.
To learn more, see our tips on writing great answers.
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
StackExchange.ready(
function () {
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fstackoverflow.com%2fquestions%2f53417422%2fconditionally-remove-elements-from-a-concurrenthashmap-thread-safe%23new-answer', 'question_page');
}
);
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Note:
Instant.now()can return a different value every time it is called. This means it doesn't remove up to the same point for all entries.– Peter Lawrey
Nov 21 '18 at 19:06