Databases
StackOverflow2013
Postsdbo
PO
 

Note that there are some explanatory texts on larger screens.

plurals
  1. PO
    primarykey
    data
    text
    <p>You really need to classify Java's Vector's type of thread safety. Javas Vector is safe to be used from multiple threads because it uses synchronization on the methods. State will not be corrupted. </p> <p>However, Java's vector's usefulness is limited from multiple threads without additional synchronization. For example, consider the simple act of reading an element from a vector</p> <pre><code>Vector vector = getVector(); if ( vector.size() &gt; 0 ) { object first = vector.get(0); } </code></pre> <p>This method will not corrupt the state of the vector, but it also is not correct. There is nothing stopping another thread from mutating the vector in between the if statement an the get() call. This code can and <strong>will</strong> eventually fail because of a race condition.</p> <p>This type of synchronization is only useful in a handfull of scenarios and it is certainly not cheap. You pay a noticable price for synchronization even if you don't use multiple threads. </p> <p>.Net chose not to pay this price by default for a scenario of only limited usefulness. Instead it chose to implement a lock free List. Authors are responsible for adding any synchronization. It's closer to C++'s model of "pay only for what you use" </p> <p>I recently wrote a couple of articles on the dangers of using collections with only internal synchronization such as Java's vector. </p> <ul> <li><a href="http://blogs.msdn.com/jaredpar/archive/2009/02/11/why-are-thread-safe-collections-so-hard.aspx" rel="noreferrer">Why are thread safe collections so hard?</a></li> <li><a href="http://blogs.msdn.com/jaredpar/archive/2009/02/16/a-more-usable-thread-safe-collection.aspx" rel="noreferrer">A more usable API for a mutable thread safe collection</a></li> </ul> <p>Reference Vector thread safety: <a href="http://www.ibm.com/developerworks/java/library/j-jtp09263.html" rel="noreferrer">http://www.ibm.com/developerworks/java/library/j-jtp09263.html</a></p>
    singulars
    1. This table or related slice is empty.
    1. POWhy is List<T> not thread-safe?
      singulars
      1. PTQuestion
    1. PTAnswer
    1. USuser
    1. USJaredPar
    plurals
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. POWhy is List<T> not thread-safe?
      singulars
      1. PTQuestion
    1. This table or related slice is empty.
    1. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    2. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    3. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    1. COSmall note: "lock free" implies "synchronized without any locks", not "no locks". http://en.wikipedia.org/wiki/Lock_free
      singulars
      1. PO
      1. USCraig Gidney
    2. COI concur with Strilanc: I had to double-take your use of the terminology "lock free".
      singulars
      1. PO
      1. USDaniel Fortunov
    3. COMethods like "Count" may be perfectly reasonably and legitimately used on a thread-safe collection, for the purpose of deciding not to bother with something. For example, if one needs to perform some operation using two items taken from a queue, a perfectly reasonable pattern might be to use a property to check the count (with a read-barrier rather than a lock) and, if the count is sufficient, acquire the lock and check the count again. If it is still sufficient, perform the operation; otherwise skip it. Release the lock in any case.
      singulars
      1. PO
      1. USsupercat
 

Querying!

 
Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload