User:Pulkit Mittal/GSOC2014/logs

Development Logs

Project Details

Project Name	STEP Libraries: Improving Thread Safety and Performance
Project Student	Pulkit Mittal
IRC(nick)	hoiji
Github (handle)	hoiji09

Milestones

Compulsary

• Thread Safety in cllazyfile Status: Review Awaiting
• Thread Safety in clstepcore Status: Started
• Thread Safety in cleditor Status: Not Started
• Thread Safety in cldai Status: Not Started
• Introduce multi-threading cllazyfile Status: Not Started

Bonus

In this section I will list down all the single threaded performance optimizations which are done in the GSOC period.

GSOC Period

Week 1

17 May (Sat):

• Figured out various functionalities in cllazyfile step library which should be made thread safe.
  These are
  1. Opening multiple files in parallel.
  2. (lazy) loading separate SDAI_Application_instance in parallel.
  3. Reading the forward / backward references of instances in parallel.
  4. Finding instances belonging to same / different types in parallel.
  5. Initializing / Setting the registry in parallel.
  6. Registering Data Sections in parallel

• Strategizing how the various features will be added into the code. Firstly a test will be created to note the existance of thread safety for the above features. If the test fail then appropriate coding will be done

18 May (Sun):

• A test was created in lazy_thread_safety_test.cc file, to check the concurrent read safety of getFwdRefs() and getRevRefs() and expectedly it failed.
• Note: to run the test, the CMakeFiles: cmake/SC_CXX_schema_macros.cmake & src/cllazyfile/CMakeLists.txt were slightly messed up.

19 May (Mon):

• Introduced getFwdRefsSafely and getRevRefsSafely which are thread safe. The thread safety test in lazy_thread_safety_test.cc passed. Submitted code through git in a branch called hj/cllazyfile-thread-safety.
• Discussed with mentor about the importance order of functionalities mentioned above. Hence will be covering the functionalities in the following order 3(done)>4>2>1>6

20-21 May (Tue, Wed):

• Noticed that getFwdRefsSafely and getRevRefsSafely are consume memory each time they are called (as separate clones are made for each invocation). (Blame the use of Judy Structure) The memory is freed only when destructor of lazyInstMgr is called. One way around this problem was to let the user call a function (say) returnFwdRefsSafely which would release the space related to a clone. Hence, I spent 2 days trying to modify the original judy code so that it allows closure of clones. But as I was not able to get a breakthrough, I have left this task for later.

22 May (Thu):

• Created a test to check the thread safety of getInstances (i.e. finding instances belonging a specific type). As expected the test failed when the number of invocations were very high. This is because getInstances internally uses find operation which is not thread safe.

23 May (Fri):

• Added the thread-safe getInstancesSafely and countInstancesSafely. Also submitted the code in github.

Week 2

24 May (Sat):

• Started working towards making lazy-loading of instances thread safe.
  • Created a test which would spawn two threads which try to load instances.
    • In the first half of iterations the threads would try to load same set of instances.
    • In the second half of iterations the threads would try to load different set of instances (not necessary disjoint).
    • For each thread within one iteration an instance would be loaded twice. This checks the case where the instance may or may-not be already loaded and the case where the instance is already loaded.
  • The problem that arose during the compilation of the test was that, finally the _mainRegistry was being used, and I had very little idea about the schemas and registries. It could not find the schema.h file.
• Couldn't work the earlier half of the day as I was traveling.

25 May (Sun):

• Got the thread safety test for lazy-loading to compile by doing certain changes in the src/cllazyfile/CMakeLists.txt.
  • This was done by including the directory ${CMAKE_BINARY_DIR}/schemas/sdai_cd209 for the above test.
  • The restriction that the above changes imposed on lazy_thread_safety_test was that, now it has to be given the the step file data/cd209/ATS1-out.stp as input.
• A potential bug was found while running the above test. The bug would appear if we follow the following steps
  1. lazyInstMgr * mgr = new lazyInstMgr;
  2. mgr->initRegistry( SchemaInit );
  3. mgr->openFile( fileName );
  4. delete mgr
  5. lazyInstMgr * mgr = new lazyInstMgr;
  6. mgr->initRegistry( SchemaInit );
  • The last step would cause assertion failure in function setRegistery. (i.e. assert( _mainRegistry == 0 )). This was solved by explicitly initializing _mainRegistry with '0' inside the lazyInstMgr constructor.
• When the test was run on the original loadInstance function, it gave assertion error related to the input stream.
• Saw the comments posted by Mark on my earlier commits. I decided to make corresponding changes in the code, once I had made lazy-loading thread safe

26 May (Mon):

• A thread-safe version of loadInstance was created. For this a fat lock was used. It is possible that we can make the lock application finer, however that has been left for later. This version passed the test successfully.
  • However their appeared to be some problem in the step file, because loading of one particular instance always failed, irrespective of the number of threads. A temporary fix was applied by removing a newline character from the step file.
  • In the loadInstance function, their was an issue of a warning instance #... not found in any section appearing even if the instance was found in the _instancesLoaded list. The fix was trivial
• A thread safe counterpart to mgr->getAdapter()->FindFileId( instanceID )->GetSTEPentity() was made. This was slightly complicated then the previous features as it consisted of 2 complex steps in different classes. Both being thread unsafe.
  • For this each thread was assigned its own mgrNodeHelper. This mgrNodeHelper was created once, for each thread and reused on later invocations.
  • Dependency was taken on thread safe loadInstanceSafely
  • The counterpart was also successfully tested

27 May (Tue):

• As per the advice given by Mark, the macro HAVE_STD_THREAD was utilized in CMakeLists.txt, including header files, mutex / thread safe functions declarations etc.
  • This opportunity was also used to clean up the CMakeLists.txt
• Fixed the newline issue encountered on 26th May. This was done by modifying the lazyfile parser by instructing it to ignore the newlines in such cases. The temporary fix was reverted back as it was no longer required.
• Prepared the changes done from 24th May in the form of multiple commits. Also the thread safe code was clubbed together wherever possible for easy identification.

28 May (Wed):

• While introducing HAVE_STD_THREAD in src/cllazyfile/lazyTypes.h a compilation problem was encountered. Somehow HAVE_STD_THREAD macro was not being recognized by lazyTypes.h. This was surprising as HAVE_STD_THREAD was recognized by lazyInstMgr.cc. The final solution was to explicitly declare HAVE_STD_THREAD through the compiler flag in src/cllazyfile/CMakeLists.txt.
• Also continuing from the last point in 27th May, the work done from 24th May was organized into 12 different commits and submitted to github.

29 May (Thu):

• Started adding a test for checking thread safety in while opening multiple files in parallel, using the same lazyInstMgr.
  • The first and foremost problem was identifying the data structures of the lazyInstMgr whose state would change when lazyInstMgr::openFile() is called. Unlike the previous functionalities here more then one data structures were involved. The following data structures were identified.
    • instanceRefs_t _fwdInstanceRefs
    • instanceRefs_t _revInstanceRefs
    • instanceTypes_t * _instanceTypes
    • instanceStreamPos_t _instanceStreamPos
    • dataSectionReaderVec_t _dataSections
    • lazyFileReaderVec_t _files
    • unsigned long _lazyInstanceCount
    • int _longestTypeNameLen
    • std::string _longestTypeName
  • The test would create two instances of lazyInstMgr, through first it would call openFile for two different files in a serial manner, through second it would call openFile for these two files parallely. Later it would compare the above data structures of both the instance managers and report any discrepancy it finds.

30 May (Fri):

• The above test was completed.
  • An extra lazyInstMgr API was added to get _instanceStreamPos data structure for comparison.
  • The test when run on existing openFile failed. Multiple reasons were attributed to the failure by running the test multiple times. Apart from gracefully failing, the test also failed many times due to segmentation fault or an assertion failure in the cllazyfile parser.

• Work was started on making the openFile thread safe.

Week 3

31 May (Sat):

• At this I was going through the dilemma of following the convention of creating different functions for thread safe code vs. using macros for demarcating code used for ensuring thread safety.
  • Continuing the former meant code duplication.
  • Switching to the latter meant that flexibility of letting the user decide which function he wants to call is thrown away.
  • I finally took the middle way decision which didn't had any of the above problem.
    • All calls to the mutex are now through a wrapper which directs the call to the mutex functionality if HAVE_STD_THREAD is defined or else to a dummy function which does nothing.
• In the thread safe counterpart of openFile, openFileSafely fine grain locking was done.
  • Mutexes were added at to safe-gaurd their respective data structures
  • Functionalities such as lazyInstMgr::registerDataSection were converted into a two step process.
  • Since it was now possible that an element of the _dataSection vector can be null the destructor for lazyInstMgr was changed accordingly.

1 June (Sun):

• The test for checking thread safety was still failing, due to assertion failure in the cllazyfile parser.
  • It was found that this is due to a static variable in sectionReader::getDelimitedKeyword. The function was reworked and named fillDelimitedKeyword. The functions taking dependence on this were slightly modified to reflect this change.
  • Another static variable in p21HeaderSectionReader was identified and tackled with.
• The test finally succeeded. Some performance statistics
  • File A: 3tnv70-asa.stp (~45mb) was taken from the site examples.
  • File B: gtc01-mme01_asm.stp (~45mb) was taken from http://downloads.openmoko.org/developer/CAD/Neo1973_IGES_STEP.zip
  • It took ~9 seconds if we tried to open either File A or File B.
  • It took ~17 seconds if we tried to open File A and then File B.
  • It took ~12.5 seconds when both the files were opened in parallel.

2 June (Mon):

• The locking in loadInstanceSafely( instanceID ) was made finer.
  • Double checking was also done to enhance performance in cases in which say:
    1. Thread A is creating a realObject belonging to instance x.
    2. Thread B comes and wants to get an object belonging to instance y.
    • If instance y has been already loaded then Thread B doesn't have to wait for Thread A. This is now handled.
• The work done from 29th May was organized into different commits and pushed to github.

3 June (Tue)

• Going through the code in src/clstepcode
  • Learnt about the various files in the library.
  • Several Problems were identified:
    • The amount of code is huge.
    • What makes the problem worse is that there are lots of small classes. Since a TDD approach is being followed it means that there will have to be lots of test files.

4-6 June (Thu - Fri)

• Very Little work done due to family reunion + travelling.

Week 4

7 June (Sat)

• Unsuccesfully tried to figure out a way to run the tests such as src/clstepcore/test/test_operators_STEPattribute.cc on my remote machine.
• Created a mutex wrapper: sc_mutex that will contain std::mutex and call its lock, unlock function if HAVE_STD_THREAD is enabled. If on the other hand HAVE_STD_THREAD is disabled, the wrapper will not contain std:mutefx and will call the dummy lock, unlock functions.
  • I will modify cllazyfile to take dependency on it later.

8 June (Sun)

• Changed the branch name from hj/cllazyfile-thread-safety to hj/thread-safety. Now I will keep all the thread-safe code in one branch.
• Modified the CMakeLists.txt of each of the library.
  • It was also found that some of the tests used the header files directly. Hence the cmake files of such libraries will have to be changed when required.