Databases
StackOverflow2013
Postsdbo
PO
 

Note that there are some explanatory texts on larger screens.

plurals
  1. PO
    primarykey
    data
    text
    <p>As the name implies, the Mutex is <code>recursive</code> but the Lock is not.</p> <p>That said, you have here a design problem. The locking operations would be better off not being accessible from the outside.</p> <pre><code>class SynchronizedInt { public: explicit SynchronizedInt(int i = 0): mData(i) {} int get() const { lock_type lock(mMutex); toolbox::ignore_unused_variable_warning(lock); return mData; } void set(int i) { lock_type lock(mMutex); toolbox::ignore_unused_variable_warning(lock); mData = i; } private: typedef boost::recursive_mutex mutex_type; typedef boost::unique_lock&lt;mutex_type&gt; lock_type; int mData; mutable mutex_type mMutex; }; </code></pre> <p>The main point of the <code>recursive_mutex</code> is to allow chain locking in a given thread which may occur if you have complex operations that call each others in some case.</p> <p>For example, let's add tweak get:</p> <pre><code>int SynchronizedInt::UnitializedValue = -1; int SynchronizedInt::get() const { lock_type lock(mMutex); if (mData == UnitializedValue) this-&gt;fetchFromCache(); return mData; } void SynchronizedInt::fetchFromCache() { this-&gt;set(this-&gt;fetchFromCacheImpl()); } </code></pre> <p>Where is the problem here ?</p> <ul> <li><code>get</code> acquires the lock on <code>mMutex</code></li> <li>it calls <code>fetchFromCache</code> which calls <code>set</code></li> <li><code>set</code> attempts to acquire the lock...</li> </ul> <p>If we did not have a <code>recursive_mutex</code>, this would fail.</p>
    singulars
    1. This table or related slice is empty.
    1. POWhy boost::recursive_mutex is not working as expected?
      singulars
      1. PTQuestion
    1. PTAnswer
    1. This table or related slice is empty.
    1. USMatthieu M.
    plurals
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    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. COThe problem is that I have a function which returns a pointer and I need ensure synchronizations on operations done outside my class. So this is why I need the lock and unlock methods, I put them inside the class to avoid the need to explicitly use boost::*_lock in the outer code. I should probably think of a better design...
      singulars
      1. PO
      1. USKjir
    2. COThere is always the solution where you return a ref counted owner to the lock to guarantee the destruction.
      singulars
      1. PO
      1. USMatthieu M.
    3. CO"_The locking operations would be better off not being accessible from the outside_" What if you need to increment `SynchronizedInt`?
      singulars
      1. PO
      1. UScuriousguy
 

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