plpy_subxactobject.c

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/*
 * the PLySubtransaction class
 *
 * src/pl/plpython/plpy_subxactobject.c
 */

#include "postgres.h"

#include "access/xact.h"
#include "executor/spi.h"

#include "plpython.h"

#include "plpy_subxactobject.h"

#include "plpy_elog.h"


List       *explicit_subtransactions = NIL;


static void PLy_subtransaction_dealloc(PyObject *subxact);
static PyObject *PLy_subtransaction_enter(PyObject *self, PyObject *unused);
static PyObject *PLy_subtransaction_exit(PyObject *self, PyObject *args);

static char PLy_subtransaction_doc[] = {
    "PostgreSQL subtransaction context manager"
};

static PyMethodDef PLy_subtransaction_methods[] = {
    {"__enter__", PLy_subtransaction_enter, METH_VARARGS, NULL},
    {"__exit__", PLy_subtransaction_exit, METH_VARARGS, NULL},
    /* user-friendly names for Python <2.6 */
    {"enter", PLy_subtransaction_enter, METH_VARARGS, NULL},
    {"exit", PLy_subtransaction_exit, METH_VARARGS, NULL},
    {NULL, NULL, 0, NULL}
};

static PyTypeObject PLy_SubtransactionType = {
    PyVarObject_HEAD_INIT(NULL, 0)
    "PLySubtransaction",        /* tp_name */
    sizeof(PLySubtransactionObject),    /* tp_size */
    0,                          /* tp_itemsize */

    /*
     * methods
     */
    PLy_subtransaction_dealloc, /* tp_dealloc */
    0,                          /* tp_print */
    0,                          /* tp_getattr */
    0,                          /* tp_setattr */
    0,                          /* tp_compare */
    0,                          /* tp_repr */
    0,                          /* tp_as_number */
    0,                          /* tp_as_sequence */
    0,                          /* tp_as_mapping */
    0,                          /* tp_hash */
    0,                          /* tp_call */
    0,                          /* tp_str */
    0,                          /* tp_getattro */
    0,                          /* tp_setattro */
    0,                          /* tp_as_buffer */
    Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE,   /* tp_flags */
    PLy_subtransaction_doc,     /* tp_doc */
    0,                          /* tp_traverse */
    0,                          /* tp_clear */
    0,                          /* tp_richcompare */
    0,                          /* tp_weaklistoffset */
    0,                          /* tp_iter */
    0,                          /* tp_iternext */
    PLy_subtransaction_methods, /* tp_tpmethods */
};


void
PLy_subtransaction_init_type(void)
{
    if (PyType_Ready(&PLy_SubtransactionType) < 0)
        elog(ERROR, "could not initialize PLy_SubtransactionType");
}

/* s = plpy.subtransaction() */
PyObject *
PLy_subtransaction_new(PyObject *self, PyObject *unused)
{
    PLySubtransactionObject *ob;

    ob = PyObject_New(PLySubtransactionObject, &PLy_SubtransactionType);

    if (ob == NULL)
        return NULL;

    ob->started = false;
    ob->exited = false;

    return (PyObject *) ob;
}

/* Python requires a dealloc function to be defined */
static void
PLy_subtransaction_dealloc(PyObject *subxact)
{
}

/*
 * subxact.__enter__() or subxact.enter()
 *
 * Start an explicit subtransaction.  SPI calls within an explicit
 * subtransaction will not start another one, so you can atomically
 * execute many SPI calls and still get a controllable exception if
 * one of them fails.
 */
static PyObject *
PLy_subtransaction_enter(PyObject *self, PyObject *unused)
{
    PLySubtransactionData *subxactdata;
    MemoryContext oldcontext;
    PLySubtransactionObject *subxact = (PLySubtransactionObject *) self;

    if (subxact->started)
    {
        PLy_exception_set(PyExc_ValueError, "this subtransaction has already been entered");
        return NULL;
    }

    if (subxact->exited)
    {
        PLy_exception_set(PyExc_ValueError, "this subtransaction has already been exited");
        return NULL;
    }

    subxact->started = true;
    oldcontext = CurrentMemoryContext;

    subxactdata = PLy_malloc(sizeof(*subxactdata));
    subxactdata->oldcontext = oldcontext;
    subxactdata->oldowner = CurrentResourceOwner;

    BeginInternalSubTransaction(NULL);
    /* Do not want to leave the previous memory context */
    MemoryContextSwitchTo(oldcontext);

    explicit_subtransactions = lcons(subxactdata, explicit_subtransactions);

    Py_INCREF(self);
    return self;
}

/*
 * subxact.__exit__(exc_type, exc, tb) or subxact.exit(exc_type, exc, tb)
 *
 * Exit an explicit subtransaction. exc_type is an exception type, exc
 * is the exception object, tb is the traceback.  If exc_type is None,
 * commit the subtransactiony, if not abort it.
 *
 * The method signature is chosen to allow subtransaction objects to
 * be used as context managers as described in
 * <http://www.python.org/dev/peps/pep-0343/>.
 */
static PyObject *
PLy_subtransaction_exit(PyObject *self, PyObject *args)
{
    PyObject   *type;
    PyObject   *value;
    PyObject   *traceback;
    PLySubtransactionData *subxactdata;
    PLySubtransactionObject *subxact = (PLySubtransactionObject *) self;

    if (!PyArg_ParseTuple(args, "OOO", &type, &value, &traceback))
        return NULL;

    if (!subxact->started)
    {
        PLy_exception_set(PyExc_ValueError, "this subtransaction has not been entered");
        return NULL;
    }

    if (subxact->exited)
    {
        PLy_exception_set(PyExc_ValueError, "this subtransaction has already been exited");
        return NULL;
    }

    if (explicit_subtransactions == NIL)
    {
        PLy_exception_set(PyExc_ValueError, "there is no subtransaction to exit from");
        return NULL;
    }

    subxact->exited = true;

    if (type != Py_None)
    {
        /* Abort the inner transaction */
        RollbackAndReleaseCurrentSubTransaction();
    }
    else
    {
        ReleaseCurrentSubTransaction();
    }

    subxactdata = (PLySubtransactionData *) linitial(explicit_subtransactions);
    explicit_subtransactions = list_delete_first(explicit_subtransactions);

    MemoryContextSwitchTo(subxactdata->oldcontext);
    CurrentResourceOwner = subxactdata->oldowner;
    PLy_free(subxactdata);

    /*
     * AtEOSubXact_SPI() should not have popped any SPI context, but just in
     * case it did, make sure we remain connected.
     */
    SPI_restore_connection();

    Py_INCREF(Py_None);
    return Py_None;
}