Interface AtomicBuffer

    • Field Detail

      • ALIGNMENT

        static final int ALIGNMENT
        Buffer alignment in bytes to ensure atomic word accesses.
        See Also:
        Constant Field Values
      • STRICT_ALIGNMENT_CHECKS_PROP_NAME

        static final java.lang.String STRICT_ALIGNMENT_CHECKS_PROP_NAME
        Name of the system property that specify if the alignment checks for atomic operations are strict. If the checks are strict then the verifyAlignment() method will throw an exception if the underlying buffer is a byte[].
        See Also:
        Constant Field Values
      • STRICT_ALIGNMENT_CHECKS

        static final boolean STRICT_ALIGNMENT_CHECKS
        Should alignment checks for atomic operations be done or not. The value is platform-dependent:
        See Also:
        STRICT_ALIGNMENT_CHECKS_PROP_NAME
    • Method Detail

      • verifyAlignment

        void verifyAlignment()
        Verify that the underlying buffer is correctly aligned to prevent word tearing, other ordering issues and the JVM crashes. In particular this method verifies that the starting offset of the underlying buffer is properly aligned. However, the actual atomic call must ensure that the index is properly aligned, i.e. it must be aligned to the size of the operand. For example a call to any of the following methods putIntOrdered(int, int), putIntVolatile(int, int), addIntOrdered(int, int), getIntVolatile(int), getAndAddInt(int, int) or getAndSetInt(int, int), must have the index aligned by four bytes (e.g. 0, 4, 8, 12, 60 etc.).

        Users are encouraged to call this method after constructing the AtomicBuffer instance in order to ensure that the underlying buffer supports atomic access to long values.

        Agrona provides an agent (org.agrona.agent.BufferAlignmentAgent) that checks the alignment of indexes for all operations at runtime. The agent throws an exception if the unaligned access is detected.

        Note: on some platforms unaligned atomic access can lead to the JVM crashes, e.g.:

         
         # Java VM: OpenJDK 64-Bit Server VM (25.352-b08 mixed mode bsd-aarch64 compressed oops)
         #
         # siginfo: si_signo: 10 (SIGBUS), si_code: 1 (BUS_ADRALN)
         
         
        Throws:
        java.lang.IllegalStateException - if the starting offset into the buffer is not properly aligned.
        See Also:
        ALIGNMENT
      • getLongVolatile

        long getLongVolatile​(int index)
        Get the value at a given index with volatile semantics.
        Parameters:
        index - in bytes from which to get.
        Returns:
        the value for at a given index.
      • putLongVolatile

        void putLongVolatile​(int index,
                             long value)
        Put a value to a given index with volatile semantics.
        Parameters:
        index - in bytes for where to put.
        value - for at a given index.
      • putLongOrdered

        void putLongOrdered​(int index,
                            long value)
        Put a value to a given index with ordered store semantics.
        Parameters:
        index - in bytes for where to put.
        value - for at a given index.
      • addLongOrdered

        long addLongOrdered​(int index,
                            long increment)
        Add a value to a given index with ordered store semantics. Use a negative increment to decrement.
        Parameters:
        index - in bytes for where to put.
        increment - by which the value at the index will be adjusted.
        Returns:
        the previous value at the index.
      • compareAndSetLong

        boolean compareAndSetLong​(int index,
                                  long expectedValue,
                                  long updateValue)
        Atomic compare and set of a long given an expected value.
        Parameters:
        index - in bytes for where to put.
        expectedValue - at to be compared.
        updateValue - to be exchanged.
        Returns:
        set successful or not.
      • getAndSetLong

        long getAndSetLong​(int index,
                           long value)
        Atomically exchange a value at a location returning the previous contents.
        Parameters:
        index - in bytes for where to put.
        value - for at a given index.
        Returns:
        previous value at the index.
      • getAndAddLong

        long getAndAddLong​(int index,
                           long delta)
        Atomically add a delta to a value at a location returning the previous contents. To decrement a negative delta can be provided.
        Parameters:
        index - in bytes for where to put.
        delta - to be added to the value at the index.
        Returns:
        previous value.
      • getIntVolatile

        int getIntVolatile​(int index)
        Get the value at a given index with volatile semantics.
        Parameters:
        index - in bytes from which to get.
        Returns:
        the value for at a given index.
      • putIntVolatile

        void putIntVolatile​(int index,
                            int value)
        Put a value to a given index with volatile semantics.
        Parameters:
        index - in bytes for where to put.
        value - for at a given index.
      • putIntOrdered

        void putIntOrdered​(int index,
                           int value)
        Put a value to a given index with ordered semantics.
        Parameters:
        index - in bytes for where to put.
        value - for at a given index.
      • addIntOrdered

        int addIntOrdered​(int index,
                          int increment)
        Add a value to a given index with ordered store semantics. Use a negative increment to decrement.
        Parameters:
        index - in bytes for where to put.
        increment - by which the value at the index will be adjusted.
        Returns:
        the previous value at the index.
      • compareAndSetInt

        boolean compareAndSetInt​(int index,
                                 int expectedValue,
                                 int updateValue)
        Atomic compare and set of an int given an expected value.
        Parameters:
        index - in bytes for where to put.
        expectedValue - at to be compared.
        updateValue - to be exchanged.
        Returns:
        successful or not.
      • getAndSetInt

        int getAndSetInt​(int index,
                         int value)
        Atomically exchange a value at a location returning the previous contents.
        Parameters:
        index - in bytes for where to put.
        value - for at a given index.
        Returns:
        previous value.
      • getAndAddInt

        int getAndAddInt​(int index,
                         int delta)
        Atomically add a delta to a value at a location returning the previous contents. To decrement a negative delta can be provided.
        Parameters:
        index - in bytes for where to put.
        delta - to be added to the value at the index.
        Returns:
        previous value.
      • getShortVolatile

        short getShortVolatile​(int index)
        Get the value at a given index with volatile semantics.
        Parameters:
        index - in bytes from which to get.
        Returns:
        the value for at a given index.
      • putShortVolatile

        void putShortVolatile​(int index,
                              short value)
        Put a value to a given index with volatile semantics.
        Parameters:
        index - in bytes for where to put.
        value - for at a given index.
      • getCharVolatile

        char getCharVolatile​(int index)
        Get the value at a given index with volatile semantics.
        Parameters:
        index - in bytes from which to get.
        Returns:
        the value for at a given index.
      • putCharVolatile

        void putCharVolatile​(int index,
                             char value)
        Put a value to a given index with volatile semantics.
        Parameters:
        index - in bytes for where to put.
        value - for at a given index.
      • getByteVolatile

        byte getByteVolatile​(int index)
        Get the value at a given index with volatile semantics.
        Parameters:
        index - in bytes from which to get.
        Returns:
        the value for at a given index.
      • putByteVolatile

        void putByteVolatile​(int index,
                             byte value)
        Put a value to a given index with volatile semantics.
        Parameters:
        index - in bytes for where to put.
        value - for at a given index.