Value objects

Each Varon-T disruptor queue manages a list of values, which are allocated and controlled by the disruptor queue. This increases performance of the queue and application by eliminating the need to perform allocations on a per object basis. Another way to think of the disruptor queue is a pool of value objects available to your applications.

The value interface is simple and is a superclass of a value managed by a Varon-T disruptor queue.

struct vrt_value

An oqaque type that serves as a superclass for ring buffer values.

Each value type in an application must implement the following interface:

struct vrt_value_type
cork_hash type_id

A type identifier for this value type. The cork-hash utility in libcork will generate a sufficient hash value for this field given a string identifier.

struct vrt_value *(*new_value)(const struct vrt_value_type *type)

Allocates, iniatializes, and returns an instance of type.

void (*free_value)(const struct vrt_value_type *type, struct vrt_value *value)

Frees any resources used by value, which must be an instance of type.

Example: Integer values

The following is a simple implementation of a new value type for storing integer values in a Varon-T disruptor queue.

#include <libcork/core.h>

struct vrt_integer_value {
    struct vrt_value  parent;
    int64_t  value;
};

static struct vrt_value *
vrt_integer__new_value(const struct vrt_value_type *type)
{
    struct vrt_integer_value  *self = cork_new(struct vrt_integer_value);
    return &self->parent;
}

static void
vrt_integer__free_value(const struct vrt_value_type *type, struct vrt_value *value)
{
    struct vrt_integer_value  *self =
        cork_container_of(value, struct vrt_integer_value, parent);
    free(self);
}

/* The following hash value is produced by the cork-hash utility function */
#define VRT_INTEGER_TYPE 0xcd6e0682

static struct vrt_value_type  _vrt_integer_type = {
    type = VRT_INTEGER_TYPE,
    vrt_integer__new_value,
    vrt_integer__free_value
};

const struct vrt_value_type *
vrt_integer_type(void)
{
    return &_vrt_integer_type;
}

The implementation is straightforward and depends on the libcork library. A few details about this implementation are worth mentioning:

  • The implementation uses embedded C structs to contain or “subclass” the vrt_value type within vrt_integer_value. The disruptor queue library can then operate efficiently on pointers to the contained or “superclass” struct. However, your application will need a pointer to the container struct when given a pointer to the contained struct in order to perform application specific computations. That is the purpose of cork_container_of().
  • The _vrt_integer_type does not require additional fields beyond the vrt_value_type interface. Therefore, it is a static value type instance and accessible through vrt_integer_type().

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