Saxon » SaxonC

I think I have finally tracked down the cause of this crash.

The bug is in the C++ code for JNI. The problem is we are not attaching the JNIenv variable in the new threads we create. Hence the java instances cannot use the JNIenv.

See the following article to a background on JNI in multithreading apps: https://stackoverflow.com/questions/31134009/how-to-keep-calling-java-instance-jobject-for-new-threads-created-by-c-in-jni

I experimented with this by attaching the JNIenv using the AttachCurrentThread method and now I am getting some expected output from the python script:

Starting Thread-1
Starting Thread-2
Thread-1 : <?xml version="1.0" encoding="UTF-8"?>Hello from SaxonC: 2022-03-10T00:05:16.241Z
Thread-2 : <?xml version="1.0" encoding="UTF-8"?>Hello from SaxonC: 2022-03-10T00:05:17.247Z
Thread-1 : <?xml version="1.0" encoding="UTF-8"?>Hello from SaxonC: 2022-03-10T00:05:17.248Z
Thread-1 : <?xml version="1.0" encoding="UTF-8"?>Hello from SaxonC: 2022-03-10T00:05:18.25Z
Thread-2 : <?xml version="1.0" encoding="UTF-8"?>Hello from SaxonC: 2022-03-10T00:05:19.251Z
Thread-1 : <?xml version="1.0" encoding="UTF-8"?>Hello from SaxonC: 2022-03-10T00:05:19.258Z
Thread-1 : <?xml version="1.0" encoding="UTF-8"?>Hello from SaxonC: 2022-03-10T00:05:20.26Z
Exiting Thread-1


JET RUNTIME HAS DETECTED UNRECOVERABLE ERROR: runtime error
Thread 30AC2 ["Thread-1"] is terminated without notifying the JVM. Probably, "DetachCurrentThread" function was not called
Please, contact the vendor of the application.
Core dump will be piped to "/usr/share/apport/apport %p %s %c %d %P %E"
Extra information about error is saved in the "jet_err_199341.txt" file.

I am now getting a DetachCurrentThread crash probably I am not cleaning things after the 1st thread has finished.

Bug fix applied to the C++ code where we check if the JNIEnv is available. If not we try to attach the JVM to the current thread.

The following method have been added to the SaxonProcessor:

    static void attachCurrentThread();

    static void detachCurrentThread();

Similarly in the PHP and, Python API.

See modified sample below:

import threading
import time

from saxonc import *

exitFlag = 0

class myThread (threading.Thread):
   def __init__(self, threadID, name, counter, proc, xquery_processor):
      threading.Thread.__init__(self)
      self.threadID = threadID
      self.name = name
      self.counter = counter
      self.xquery_processor = xquery_processor
      self.proc = proc
   def run(self):
      print ("Starting " + self.name)
      example(self.name, self.counter, 5, self.proc, self.xquery_processor)
      print ("Exiting " + self.name)

def example(threadName, delay, counter, proc, xquery_processor):
         while counter>0:
            if exitFlag:
               threadName.exit()
            time.sleep(delay)

            result = xquery_processor.run_query_to_string(query_text = '"Hello from SaxonC: " || current-dateTime()')
            
            if result is None:
               threadName.exit()

            print("%s : %s" % (threadName, result))
            counter -= 1
            proc.detach_current_thread

def example2(threadName, delay, counter, xquery_processor):
   while counter>0:
      if exitFlag:
         return
      time.sleep(delay)
      result = xquery_processor.run_query_to_string(query_text = '"Hello from SaxonC: " || current-dateTime()')
      if result is None:
         return
      print("%s : %s" % (threadName, result))
      counter -= 1


saxon_proc = PySaxonProcessor(license = False)

# Create new threads
thread1 = myThread(1, "Thread-1", 1, saxon_proc, saxon_proc.new_xquery_processor())
thread2 = myThread(2, "Thread-2", 2, saxon_proc, saxon_proc.new_xquery_processor())

# Start new Threads
thread1.start()
thread2.start()
thread1.join()
thread2.join()
print ("Exiting Main Thread")

Output:

Starting Thread-1
Starting Thread-2
Thread-1 : <?xml version="1.0" encoding="UTF-8"?>Hello from SaxonC: 2022-03-10T18:35:30.021Z
Thread-2 : <?xml version="1.0" encoding="UTF-8"?>Hello from SaxonC: 2022-03-10T18:35:31.026Z
Thread-1 : <?xml version="1.0" encoding="UTF-8"?>Hello from SaxonC: 2022-03-10T18:35:31.027Z
Thread-1 : <?xml version="1.0" encoding="UTF-8"?>Hello from SaxonC: 2022-03-10T18:35:32.029Z
Thread-2 : <?xml version="1.0" encoding="UTF-8"?>Hello from SaxonC: 2022-03-10T18:35:33.03Z
Thread-1 : <?xml version="1.0" encoding="UTF-8"?>Hello from SaxonC: 2022-03-10T18:35:33.036Z
Thread-1 : <?xml version="1.0" encoding="UTF-8"?>Hello from SaxonC: 2022-03-10T18:35:34.039Z
Exiting Thread-1
Thread-2 : <?xml version="1.0" encoding="UTF-8"?>Hello from SaxonC: 2022-03-10T18:35:35.033Z
Thread-2 : <?xml version="1.0" encoding="UTF-8"?>Hello from SaxonC: 2022-03-10T18:35:37.043Z
Thread-2 : <?xml version="1.0" encoding="UTF-8"?>Hello from SaxonC: 2022-03-10T18:35:39.046Z
Exiting Thread-2
Exiting Main Thread

Yes it is intended and working in the example code. It is a class property.

Available in the next maintenance release.

Bug fix applied in the SaxonC 11.3 maintenance release.