Re: Safety Of Non-Synchronized Collections
On 1/9/13 4:26 PM, Lew wrote:
Daniel Pitts wrote:
Lew wrote:
Daniel Pitts wrote:
Lew wrote:
Roedy Green wrote:
Lew wrote, quoted or indirectly quoted someone who said :
Well, there's the fact that StringBuffer is not thread-safe.
Sun advertised it as such even if it were not perfectly so. When
Never saw it advertised as such myself.
...
Directly in StringBuffer JavaDoc, where you'd expect.
From <http://docs.oracle.com/javase/7/docs/api/java/lang/StringBuffer.html>
The first two paragraphs:
A thread-safe, mutable sequence of characters. A string buffer is like a String, but can be modified. At any point in time it contains some particular sequence of characters, but the length and content of the sequence can be changed through certain method calls.
String buffers are safe for use by multiple threads. The methods are synchronized where necessary so that all the operations on any particular instance behave as if they occur in some serial order that is consistent with the order of the method calls made by each of the individual threads involved.
They lied.
'StringBuffer' is no more thread safe than any other class with synchronized methods.
Which is more safe than other classes without synchronized methods.
But safe is binary. "More safe" if less than 100% still is "unsafe".
They are thread-safe to the point that each method call is atomic. What
else could you ask for? They didn't lie.
I could ask for complete thread safety, which synchronized methods do not guarantee.
They did lie.
http://rayfd.me/2007/11/11/when-a-synchronized-class-isnt-threadsafe/
This is elementary concurrency gotcha lore.
Wow, you mean if I don't use an API as intended, it doesn't work as
intended? Sarcasm aside, a Thread-Safe class means the methods on it
can be called concurrently, and the operations are performed as
described. If you don't have any consideration for thread safety in
your class, then data could get mangled and unexpected/undefined
behavior could happen.
Now, operations may or may not be thread-safe, externally to whether or
not they operate on a thread-safe class. Any operation which must be
atomic with regards to the state of that class needs to either be a CAS
style operation (update the state if the state hasn't already been
updated), a single operation synchronized against the common lock
object, or externally managed.