Difference between revisions of "Locking in JANA"
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(Created page with "* Do not place use any locks in JEventProcessor::init(), they are unnecessary, and a waste of time: JANA is guaranteed to be single-threaded in this function") |
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| − | * Do not place use any locks in JEventProcessor::init() | + | * Do not place use any locks in JEventProcessor::init(): they are unnecessary, and a waste of time. |
| + | ** JANA is guaranteed to be single-threaded in this function. | ||
| + | |||
| + | * Do not use or modify any global variables, unless you are in a lock. | ||
| + | ** Or even better, don't have any in the first place. It's terrible programming practice. | ||
| + | |||
| + | * Do NOT use or modify any class member-variables that you define for your JEventProcessor (i.e. in header file), unless you are in a lock (or in init()). These variables can be modified by other threads. | ||
| + | ** This ESPECIALLY includes data saved in brun(), that is read in evnt(). | ||
| + | ** Or even better, don't have any in the first place: Reduce the amount of time spent in locks if at all possible. Use function-scope (local) variables instead. | ||
| + | |||
| + | * If you are creating histograms or trees (outside of init()): Use the global ROOT JANA lock functions below. | ||
| + | ** This is because they depend on gDirectory being constant. | ||
| + | <syntaxhighlight> | ||
| + | japp->RootWriteLock(); //ACQUIRE ROOT LOCK | ||
| + | japp->RootUnLock(); //RELEASE ROOT LOCK | ||
| + | </syntaxhighlight> | ||
| + | |||
| + | === Filling Histograms === | ||
| + | * If you are filling histograms, you do NOT need to grab the global ROOT JANA lock functions. Try to instead grab a lock with a smaller scope, so that other threads can write to other histograms that don't interfere with yours. | ||
| + | ** In you are directly in the plugin processor, there's a special function to do this, that locks for the current plugin only. It is: | ||
| + | <syntaxhighlight> | ||
| + | japp->RootFillLock(this); //ACQUIRE ROOT FILL LOCK //this: JEventProcessor pointer | ||
| + | japp->RootFillUnLock(this); //RELEASE ROOT FILL LOCK //this: JEventProcessor pointer | ||
| + | </syntaxhighlight> | ||
| + | |||
| + | === Filling TTrees === | ||
| + | |||
| + | * If you are filling TTrees to the global ROOT file (i.e. hd_root.root), write to the TTrees with the global ROOT JANA lock functions below: | ||
| + | ** This is because TTree::Fill() periodically writes to the file, modifying it. | ||
| + | <syntaxhighlight> | ||
| + | japp->RootWriteLock(); //ACQUIRE ROOT LOCK | ||
| + | japp->RootUnLock(); //RELEASE ROOT LOCK | ||
| + | </syntaxhighlight> | ||
| + | |||
| + | * If you are filling TTrees to a local ROOT file (i.e. NOT hd_root.root), you do NOT need to grab the global ROOT JANA lock functions. Try to instead grab a lock with a smaller scope, so that other threads can write to other trees that don't interfere with yours. | ||
| + | ** Grab the same for every tree that is written to the same output file. This is because TTree::Fill() periodically writes to the file, modifying it. | ||
| + | ** This can be done with: | ||
| + | <syntaxhighlight> | ||
| + | japp->WriteLock("MyFileName"); //ACQUIRE FILE LOCK | ||
| + | japp->Unlock("MyFileName"); //RELEASE FILE LOCK | ||
| + | </syntaxhighlight> | ||
Revision as of 10:24, 11 April 2016
- Do not place use any locks in JEventProcessor::init(): they are unnecessary, and a waste of time.
- JANA is guaranteed to be single-threaded in this function.
- Do not use or modify any global variables, unless you are in a lock.
- Or even better, don't have any in the first place. It's terrible programming practice.
- Do NOT use or modify any class member-variables that you define for your JEventProcessor (i.e. in header file), unless you are in a lock (or in init()). These variables can be modified by other threads.
- This ESPECIALLY includes data saved in brun(), that is read in evnt().
- Or even better, don't have any in the first place: Reduce the amount of time spent in locks if at all possible. Use function-scope (local) variables instead.
- If you are creating histograms or trees (outside of init()): Use the global ROOT JANA lock functions below.
- This is because they depend on gDirectory being constant.
japp->RootWriteLock(); //ACQUIRE ROOT LOCK japp->RootUnLock(); //RELEASE ROOT LOCK
Filling Histograms
- If you are filling histograms, you do NOT need to grab the global ROOT JANA lock functions. Try to instead grab a lock with a smaller scope, so that other threads can write to other histograms that don't interfere with yours.
- In you are directly in the plugin processor, there's a special function to do this, that locks for the current plugin only. It is:
japp->RootFillLock(this); //ACQUIRE ROOT FILL LOCK //this: JEventProcessor pointer japp->RootFillUnLock(this); //RELEASE ROOT FILL LOCK //this: JEventProcessor pointer
Filling TTrees
- If you are filling TTrees to the global ROOT file (i.e. hd_root.root), write to the TTrees with the global ROOT JANA lock functions below:
- This is because TTree::Fill() periodically writes to the file, modifying it.
japp->RootWriteLock(); //ACQUIRE ROOT LOCK japp->RootUnLock(); //RELEASE ROOT LOCK
- If you are filling TTrees to a local ROOT file (i.e. NOT hd_root.root), you do NOT need to grab the global ROOT JANA lock functions. Try to instead grab a lock with a smaller scope, so that other threads can write to other trees that don't interfere with yours.
- Grab the same for every tree that is written to the same output file. This is because TTree::Fill() periodically writes to the file, modifying it.
- This can be done with:
japp->WriteLock("MyFileName"); //ACQUIRE FILE LOCK japp->Unlock("MyFileName"); //RELEASE FILE LOCK
