Package org.apache.derby.iapi.util

Class InterruptStatus

  • public class InterruptStatus
extends java.lang.Object
    Static methods to save and retrieve information about a (session) thread's interrupt status flag. If during operation we notice an interrupt, Derby will either:
    • immediately throw an exception to cut execution short, also resurrecting the thread's interrupted status flag. This does not require use of this class.
    • just note the fact using this class (noteAndClearInterrupt, or (setInterrupted)), and retry whatever got interrupted, continuing execution. To achieve this, Derby will always temporarily clear the interrupted status flag. Later, depending on the type of SQL statement, we may wish to interrupt execution by throwing an SQLException at a safe place, say, after a statement in a batch is complete (throwIf), or just let the execution run to completion, and then just prior to returning to the appliction, the thread's interrupted status flag will resurrected (restoreIntrFlagIfSeen)
    Normally, the information is saved away in the session's LanguageConnectionContext, if available. If not, we save it in a thread local variable.

    • Field Summary

      Fields 
      Modifier and Type Field Description
      private static java.lang.ThreadLocal<java.lang.Exception> exception
      Use thread local variable to store interrupt status flag *only* if we don't have lcc, e.g. during database creation, shutdown etc.
      static int INTERRUPT_RETRY_SLEEP  
      static int MAX_INTERRUPT_RETRIES
      Constants used by code that retries file operations after seeing the NIO file channel closed due to interrupts.

    • Constructor Summary

      Constructors 
      Constructor Description
      InterruptStatus()  

    • Method Summary

      All Methods Static Methods Concrete Methods 
      Modifier and Type Method Description
      private static Context getContextOrNull​(java.lang.String contextID)
      Privileged lookup of a Context.
      static boolean noteAndClearInterrupt​(java.lang.String s, int threadsInPageIO, int hashCode)
      Checks if the thread has been interrupted in NIO, presumably because we saw an exception indicating this.
      static void restoreIntrFlagIfSeen()
      Check if the we ever noticed and reset the thread's interrupt status flag to allow safe operation during execution.
      static void restoreIntrFlagIfSeen​(LanguageConnectionContext lcc)
      Same purpose as restoreIntrFlagIfSeen().
      static void saveInfoFromLcc​(LanguageConnectionContext lcc)
      Use when lcc is dying to save info in thread local instead.
      static void setInterrupted()
      Make a note that this thread saw an interrupt.
      static void throwIf​(LanguageConnectionContext lcc)
      Check if the we ever noticed and reset the thread's interrupt status flag to allow safe operation during execution, or if the interrupt status flag is set now.

      • Methods inherited from class java.lang.Object

        clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

    • Field Detail

      • MAX_INTERRUPT_RETRIES

        public static final int MAX_INTERRUPT_RETRIES
        Constants used by code that retries file operations after seeing the NIO file channel closed due to interrupts.
        See Also:
        Constant Field Values

      • exception

        private static final java.lang.ThreadLocal<java.lang.Exception> exception
        Use thread local variable to store interrupt status flag *only* if we don't have lcc, e.g. during database creation, shutdown etc.

    • Constructor Detail

      • InterruptStatus

        public InterruptStatus()

    • Method Detail

      • setInterrupted

        public static void setInterrupted()
        Make a note that this thread saw an interrupt. Thread's intr status flag is presumably off already, but we reset it here also. Use lcc if available, else thread local variable.

      • saveInfoFromLcc

        public static void saveInfoFromLcc​(LanguageConnectionContext lcc)
        Use when lcc is dying to save info in thread local instead. Useful under shutdown.

      • noteAndClearInterrupt

        public static boolean noteAndClearInterrupt​(java.lang.String s,
                                            int threadsInPageIO,
                                            int hashCode)
        Checks if the thread has been interrupted in NIO, presumably because we saw an exception indicating this. Make a note of this and clear the thread's interrupt status flag (NIO doesn't clear it when throwing) so we can retry whatever we are doing. It will be set back ON before control is transferred back to the application, cf. restoreIntrFlagIfSeen.

        The note that we saw an interrupt is stored in the lcc if available, if not, in thread local exception.

        Parameters:
        s - (debug info) whence
        threadsInPageIO - (debug info) number of threads inside the NIO code concurrently
        hashCode - (debug info) container id
        Returns:
        true if the thread's interrupt status flag was set

      • restoreIntrFlagIfSeen

        public static void restoreIntrFlagIfSeen()
        Check if the we ever noticed and reset the thread's interrupt status flag to allow safe operation during execution. Called from JDBC API methods before returning control to user application. Typically, this happens just prior to return in methods that catch Throwable and invoke handleException (directly or indirectly) on it, e.g. 
               :
       InterruptStatus.restoreIntrFlagIfSeen();
       return ...;
    } catch (Throwable t) {
       throw handleException(t);
    }
        handleException does its own calls to restoreIntrFlagIfSeen. If setupContextStack has been called consider using the overloaded variant of restoreIntrFlagIfSeen with an lcc argument.

        If an interrupt status flag was seen, we set it back on here.

      • restoreIntrFlagIfSeen

        public static void restoreIntrFlagIfSeen​(LanguageConnectionContext lcc)
        Same purpose as restoreIntrFlagIfSeen(). This variant presumes we are sure we have a lcc != null, i.e. setupContextStack has been called and not yet restored. Note that we cannot merge this code with restoreContextStack, since that is typically called in a finally block, at which point in time, the lcc may be gone due to errors of severity SESSION_SEVERITY or DATABASE_SEVERITY.

        If no lcc is available, use the zero-arg variant. We only need this variant for performance reasons.

        Parameters:
        lcc - the language connection context for this session

      • throwIf

        public static void throwIf​(LanguageConnectionContext lcc)
                    throws StandardException
        Check if the we ever noticed and reset the thread's interrupt status flag to allow safe operation during execution, or if the interrupt status flag is set now. Called when operations want to be prematurely terminated due to interrupt.

        If an interrupt status flag was seen, but temporarily switched off, we set it back ON here.

        Parameters:
        lcc - the language connection context for this session
        Throws:
        StandardException - (session level SQLState.CONN_INTERRUPT) if interrupt seen

      • getContextOrNull

        private static Context getContextOrNull​(java.lang.String contextID)
        Privileged lookup of a Context. Must be private so that user code can't call this entry point.