Comments on: Concurrency and HashMap http://blog.webscale.co.in/?p=25 Just another WordPress weblog Sun, 27 Jun 2010 15:52:43 +0000 http://wordpress.org/?v=2.9.2 hourly 1 By: Michael B http://blog.webscale.co.in/?p=25&cpage=1#comment-62 Michael B Tue, 01 Jul 2008 21:49:43 +0000 http://pitfalls.wordpress.com/?p=25#comment-62 "Finally i will leave you with this interesting bug in Java which says HashMap can..." Wrong choice of words as it's not a bug. A pitfall for the uninitiated? sure. not thread-safe means not thread-safe. It's a visibility issue that is goign to stay in there as it's outside the scope of what a hashmap is suppose to do, use a ConcurrentMap implementation. For an other perfect example where ppl also used there 'smart creativity' check out: http://www.cs.umd.edu/~pugh/java/memoryModel/DoubleCheckedLocking.html dj wrote: "Nicely written. But I was not able to reproduce it. any clues ?" Try reading this blog: http://java.dzone.com/articles/but-it-works-on-my-machine In short the jvm you used might provide more visibility that it has too. The bottom line that which isn't guaranteed to work is going to bit you in the ass -> small adaptation of murphies law. “Finally i will leave you with this interesting bug in Java which says HashMap can…”
Wrong choice of words as it’s not a bug. A pitfall for the uninitiated? sure.

not thread-safe means not thread-safe. It’s a visibility issue that is goign to stay in there as it’s outside the scope of what a hashmap is suppose to do, use a ConcurrentMap implementation.

For an other perfect example where ppl also used there ’smart creativity’ check out:
http://www.cs.umd.edu/~pugh/java/memoryModel/DoubleCheckedLocking.html

dj wrote:
“Nicely written. But I was not able to reproduce it. any clues ?”
Try reading this blog: http://java.dzone.com/articles/but-it-works-on-my-machine
In short the jvm you used might provide more visibility that it has too. The bottom line that which isn’t guaranteed to work is going to bit you in the ass -> small adaptation of murphies law.

]]> By: dj http://blog.webscale.co.in/?p=25&cpage=1#comment-61 dj Tue, 01 Jul 2008 04:34:56 +0000 http://pitfalls.wordpress.com/?p=25#comment-61 Nicely written. But I was not able to reproduce it. any clues ? Nicely written. But I was not able to reproduce it. any clues ?

]]> By: James http://blog.webscale.co.in/?p=25&cpage=1#comment-63 James Mon, 30 Jun 2008 06:20:22 +0000 http://pitfalls.wordpress.com/?p=25#comment-63 Nice, well explained article. I think this could do really well on JavaLobby. If you're interested in reposting there, send me a mail and we can organise it James Nice, well explained article. I think this could do really well on JavaLobby. If you’re interested in reposting there, send me a mail and we can organise it

James

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