plpy_subxactobject.c

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/*
 * the PLySubtransaction class
 *
 * src/pl/plpython/plpy_subxactobject.c
 */
 
#include "postgres.h"
 
#include "access/xact.h"
#include "plpy_elog.h"
#include "plpy_subxactobject.h"
#include "plpython.h"
#include "utils/memutils.h"
 
List       *explicit_subtransactions = NIL;
 
 
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 PyType_Slot PLySubtransaction_slots[] =
{
    {
        Py_tp_doc, (char *) PLy_subtransaction_doc
    },
    {
        Py_tp_methods, PLy_subtransaction_methods
    },
    {
        0, NULL
    }
};
 
static PyType_Spec PLySubtransaction_spec =
{
    .name = "PLySubtransaction",
        .basicsize = sizeof(PLySubtransactionObject),
        .flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE,
        .slots = PLySubtransaction_slots,
};
 
static PyTypeObject *PLy_SubtransactionType;
 
 
void
PLy_subtransaction_init_type(void)
{
    PLy_SubtransactionType = (PyTypeObject *) PyType_FromSpec(&PLySubtransaction_spec);
    if (!PLy_SubtransactionType)
        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;
#if PY_VERSION_HEX < 0x03080000
    /* Workaround for Python issue 35810; no longer necessary in Python 3.8 */
    Py_INCREF(PLy_SubtransactionType);
#endif
 
    ob->started = false;
    ob->exited = false;
 
    return (PyObject *) ob;
}
 
/*
 * 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 = (PLySubtransactionData *)
        MemoryContextAlloc(TopTransactionContext,
                           sizeof(PLySubtransactionData));
 
    subxactdata->oldcontext = oldcontext;
    subxactdata->oldowner = CurrentResourceOwner;
 
    BeginInternalSubTransaction(NULL);
 
    /* Be sure that cells of explicit_subtransactions list are long-lived */
    MemoryContextSwitchTo(TopTransactionContext);
    explicit_subtransactions = lcons(subxactdata, explicit_subtransactions);
 
    /* Caller wants to stay in original memory context */
    MemoryContextSwitchTo(oldcontext);
 
    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 subtransaction, 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;
    pfree(subxactdata);
 
    Py_RETURN_NONE;
}