tracer.c

/* Licensed under the Apache License: http://www.apache.org/licenses/LICENSE-2.0 */
/* For details: https://github.com/nedbat/coveragepy/blob/master/NOTICE.txt */

/* C-based Tracer for coverage.py. */

#include "util.h"
#include "datastack.h"
#include "filedisp.h"
#include "tracer.h"

/* Python C API helpers. */

static int
pyint_as_int(PyObject * pyint, int *pint)
{
    int the_int = (int)PyLong_AsLong(pyint);
    if (the_int == -1 && PyErr_Occurred()) {
        return RET_ERROR;
    }

    *pint = the_int;
    return RET_OK;
}


/* Interned strings to speed GetAttr etc. */

static PyObject *str_trace;
static PyObject *str_file_tracer;
static PyObject *str__coverage_enabled;
static PyObject *str__coverage_plugin;
static PyObject *str__coverage_plugin_name;
static PyObject *str_dynamic_source_filename;
static PyObject *str_line_number_range;

int
CTracer_intern_strings(void)
{
    int ret = RET_ERROR;

#define INTERN_STRING(v, s)                     \
    v = PyUnicode_InternFromString(s);          \
    if (v == NULL) {                            \
        goto error;                             \
    }

    INTERN_STRING(str_trace, "trace")
    INTERN_STRING(str_file_tracer, "file_tracer")
    INTERN_STRING(str__coverage_enabled, "_coverage_enabled")
    INTERN_STRING(str__coverage_plugin, "_coverage_plugin")
    INTERN_STRING(str__coverage_plugin_name, "_coverage_plugin_name")
    INTERN_STRING(str_dynamic_source_filename, "dynamic_source_filename")
    INTERN_STRING(str_line_number_range, "line_number_range")

    ret = RET_OK;

error:
    return ret;
}

static void CTracer_disable_plugin(CTracer *self, PyObject * disposition);

static int
CTracer_init(CTracer *self, PyObject *args_unused, PyObject *kwds_unused)
{
    int ret = RET_ERROR;

    if (DataStack_init(&self->stats, &self->data_stack) < 0) {
        goto error;
    }

    self->pdata_stack = &self->data_stack;

    self->context = Py_None;
    Py_INCREF(self->context);

    ret = RET_OK;
    goto ok;

error:
    STATS( self->stats.errors++; )

ok:
    return ret;
}

static void
CTracer_dealloc(CTracer *self)
{
    int i;

    if (self->started) {
        PyEval_SetTrace(NULL, NULL);
    }

    Py_XDECREF(self->should_trace);
    Py_XDECREF(self->check_include);
    Py_XDECREF(self->warn);
    Py_XDECREF(self->concur_id_func);
    Py_XDECREF(self->data);
    Py_XDECREF(self->file_tracers);
    Py_XDECREF(self->should_trace_cache);
    Py_XDECREF(self->should_start_context);
    Py_XDECREF(self->switch_context);
    Py_XDECREF(self->context);
    Py_XDECREF(self->disable_plugin);

    DataStack_dealloc(&self->stats, &self->data_stack);
    if (self->data_stacks) {
        for (i = 0; i < self->data_stacks_used; i++) {
            DataStack_dealloc(&self->stats, self->data_stacks + i);
        }
        PyMem_Free(self->data_stacks);
    }

    Py_XDECREF(self->data_stack_index);

    Py_TYPE(self)->tp_free((PyObject*)self);
}

#if TRACE_LOG
static const char *
indent(int n)
{
    static const char * spaces =
        "                                                                    "
        "                                                                    "
        "                                                                    "
        "                                                                    "
        ;
    return spaces + strlen(spaces) - n*2;
}

static BOOL logging = FALSE;
/* Set these constants to be a file substring and line number to start logging. */
static const char * start_file = "nested.py";
static int start_line = 1;

static void
CTracer_showlog(CTracer * self, int lineno, PyObject * filename, const char * msg)
{
    if (logging) {
        int depth = self->pdata_stack->depth;
        printf("%x: %s%3d ", (int)self, indent(depth), depth);
        if (lineno) {
            printf("%4d", lineno);
        }
        else {
            printf("    ");
        }
        if (filename) {
            PyObject *ascii = PyUnicode_AsASCIIString(filename);
            printf(" %s", PyBytes_AS_STRING(ascii));
            Py_DECREF(ascii);
        }
        if (msg) {
            printf(" %s", msg);
        }
        printf("\n");
    }
}

#define SHOWLOG(l,f,m)    CTracer_showlog(self,l,f,m)
#else
#define SHOWLOG(l,f,m)
#endif /* TRACE_LOG */

#if WHAT_LOG
static const char * what_sym[] = {"CALL", "EXC ", "LINE", "RET "};
#endif

/* Record a pair of integers in self->pcur_entry->file_data. */
static int
CTracer_record_pair(CTracer *self, int l1, int l2)
{
    int ret = RET_ERROR;

    PyObject * t = NULL;

    t = Py_BuildValue("(ii)", l1, l2);
    if (t == NULL) {
        goto error;
    }

    if (PySet_Add(self->pcur_entry->file_data, t) < 0) {
        goto error;
    }

    ret = RET_OK;

error:
    Py_XDECREF(t);

    return ret;
}

/* Set self->pdata_stack to the proper data_stack to use. */
static int
CTracer_set_pdata_stack(CTracer *self)
{
    int ret = RET_ERROR;
    PyObject * co_obj = NULL;
    PyObject * stack_index = NULL;

    if (self->concur_id_func != Py_None) {
        int the_index = 0;

        if (self->data_stack_index == NULL) {
            PyObject * weakref = NULL;

            weakref = PyImport_ImportModule("weakref");
            if (weakref == NULL) {
                goto error;
            }
            STATS( self->stats.pycalls++; )
            self->data_stack_index = PyObject_CallMethod(weakref, "WeakKeyDictionary", NULL);
            Py_XDECREF(weakref);

            if (self->data_stack_index == NULL) {
                goto error;
            }
        }

        STATS( self->stats.pycalls++; )
        co_obj = PyObject_CallObject(self->concur_id_func, NULL);
        if (co_obj == NULL) {
            goto error;
        }
        stack_index = PyObject_GetItem(self->data_stack_index, co_obj);
        if (stack_index == NULL) {
            /* PyObject_GetItem sets an exception if it didn't find the thing. */
            PyErr_Clear();

            /* A new concurrency object.  Make a new data stack. */
            the_index = self->data_stacks_used;
            stack_index = PyLong_FromLong((long)the_index);
            if (stack_index == NULL) {
                goto error;
            }
            if (PyObject_SetItem(self->data_stack_index, co_obj, stack_index) < 0) {
                goto error;
            }
            self->data_stacks_used++;
            if (self->data_stacks_used >= self->data_stacks_alloc) {
                int bigger = self->data_stacks_alloc + 10;
                DataStack * bigger_stacks = PyMem_Realloc(self->data_stacks, bigger * sizeof(DataStack));
                if (bigger_stacks == NULL) {
                    PyErr_NoMemory();
                    goto error;
                }
                self->data_stacks = bigger_stacks;
                self->data_stacks_alloc = bigger;
            }
            DataStack_init(&self->stats, &self->data_stacks[the_index]);
        }
        else {
            if (pyint_as_int(stack_index, &the_index) < 0) {
                goto error;
            }
        }

        self->pdata_stack = &self->data_stacks[the_index];
    }
    else {
        self->pdata_stack = &self->data_stack;
    }

    ret = RET_OK;

error:

    Py_XDECREF(co_obj);
    Py_XDECREF(stack_index);

    return ret;
}

/*
 * Parts of the trace function.
 */

static int
CTracer_check_missing_return(CTracer *self, PyFrameObject *frame)
{
    int ret = RET_ERROR;

    if (self->last_exc_back) {
        if (frame == self->last_exc_back) {
            /* Looks like someone forgot to send a return event. We'll clear
               the exception state and do the RETURN code here.  Notice that the
               frame we have in hand here is not the correct frame for the RETURN,
               that frame is gone.  Our handling for RETURN doesn't need the
               actual frame, but we do log it, so that will look a little off if
               you're looking at the detailed log.

               If someday we need to examine the frame when doing RETURN, then
               we'll need to keep more of the missed frame's state.
            */
            STATS( self->stats.missed_returns++; )
            if (CTracer_set_pdata_stack(self) < 0) {
                goto error;
            }
            if (self->pdata_stack->depth >= 0) {
                if (self->tracing_arcs && self->pcur_entry->file_data) {
                    if (CTracer_record_pair(self, self->pcur_entry->last_line, -self->last_exc_firstlineno) < 0) {
                        goto error;
                    }
                }
                SHOWLOG(PyFrame_GetLineNumber(frame), MyFrame_GetCode(frame)->co_filename, "missedreturn");
                self->pdata_stack->depth--;
                self->pcur_entry = &self->pdata_stack->stack[self->pdata_stack->depth];
            }
        }
        self->last_exc_back = NULL;
    }

    ret = RET_OK;

error:

    return ret;
}

static int
CTracer_handle_call(CTracer *self, PyFrameObject *frame)
{
    int ret = RET_ERROR;
    int ret2;

    /* Owned references that we clean up at the very end of the function. */
    PyObject * disposition = NULL;
    PyObject * plugin = NULL;
    PyObject * plugin_name = NULL;
    PyObject * next_tracename = NULL;

    /* Borrowed references. */
    PyObject * filename = NULL;
    PyObject * disp_trace = NULL;
    PyObject * tracename = NULL;
    PyObject * file_tracer = NULL;
    PyObject * has_dynamic_filename = NULL;

    CFileDisposition * pdisp = NULL;

    STATS( self->stats.calls++; )

    /* Grow the stack. */
    if (CTracer_set_pdata_stack(self) < 0) {
        goto error;
    }
    if (DataStack_grow(&self->stats, self->pdata_stack) < 0) {
        goto error;
    }
    self->pcur_entry = &self->pdata_stack->stack[self->pdata_stack->depth];

    /* See if this frame begins a new context. */
    if (self->should_start_context != Py_None && self->context == Py_None) {
        PyObject * context;
        /* We're looking for our context, ask should_start_context if this is the start. */
        STATS( self->stats.start_context_calls++; )
        STATS( self->stats.pycalls++; )
        context = PyObject_CallFunctionObjArgs(self->should_start_context, frame, NULL);
        if (context == NULL) {
            goto error;
        }
        if (context != Py_None) {
            PyObject * val;
            Py_DECREF(self->context);
            self->context = context;
            self->pcur_entry->started_context = TRUE;
            STATS( self->stats.pycalls++; )
            val = PyObject_CallFunctionObjArgs(self->switch_context, context, NULL);
            if (val == NULL) {
                goto error;
            }
            Py_DECREF(val);
        }
        else {
            Py_DECREF(context);
            self->pcur_entry->started_context = FALSE;
        }
    }
    else {
        self->pcur_entry->started_context = FALSE;
    }

    /* Check if we should trace this line. */
    filename = MyFrame_GetCode(frame)->co_filename;
    disposition = PyDict_GetItem(self->should_trace_cache, filename);
    if (disposition == NULL) {
        if (PyErr_Occurred()) {
            goto error;
        }
        STATS( self->stats.files++; )

        /* We've never considered this file before. */
        /* Ask should_trace about it. */
        STATS( self->stats.pycalls++; )
        disposition = PyObject_CallFunctionObjArgs(self->should_trace, filename, frame, NULL);
        if (disposition == NULL) {
            /* An error occurred inside should_trace. */
            goto error;
        }
        if (PyDict_SetItem(self->should_trace_cache, filename, disposition) < 0) {
            goto error;
        }
    }
    else {
        Py_INCREF(disposition);
    }

    if (disposition == Py_None) {
        /* A later check_include returned false, so don't trace it. */
        disp_trace = Py_False;
    }
    else {
        /* The object we got is a CFileDisposition, use it efficiently. */
        pdisp = (CFileDisposition *) disposition;
        disp_trace = pdisp->trace;
        if (disp_trace == NULL) {
            goto error;
        }
    }

    if (disp_trace == Py_True) {
        /* If tracename is a string, then we're supposed to trace. */
        tracename = pdisp->source_filename;
        if (tracename == NULL) {
            goto error;
        }
        file_tracer = pdisp->file_tracer;
        if (file_tracer == NULL) {
            goto error;
        }
        if (file_tracer != Py_None) {
            plugin = PyObject_GetAttr(file_tracer, str__coverage_plugin);
            if (plugin == NULL) {
                goto error;
            }
            plugin_name = PyObject_GetAttr(plugin, str__coverage_plugin_name);
            if (plugin_name == NULL) {
                goto error;
            }
        }
        has_dynamic_filename = pdisp->has_dynamic_filename;
        if (has_dynamic_filename == NULL) {
            goto error;
        }
        if (has_dynamic_filename == Py_True) {
            STATS( self->stats.pycalls++; )
            next_tracename = PyObject_CallMethodObjArgs(
                file_tracer, str_dynamic_source_filename,
                tracename, frame, NULL
                );
            if (next_tracename == NULL) {
                /* An exception from the function. Alert the user with a
                 * warning and a traceback.
                 */
                CTracer_disable_plugin(self, disposition);
                /* Because we handled the error, goto ok. */
                goto ok;
            }
            tracename = next_tracename;

            if (tracename != Py_None) {
                /* Check the dynamic source filename against the include rules. */
                PyObject * included = NULL;
                int should_include;
                included = PyDict_GetItem(self->should_trace_cache, tracename);
                if (included == NULL) {
                    PyObject * should_include_bool;
                    if (PyErr_Occurred()) {
                        goto error;
                    }
                    STATS( self->stats.files++; )
                    STATS( self->stats.pycalls++; )
                    should_include_bool = PyObject_CallFunctionObjArgs(self->check_include, tracename, frame, NULL);
                    if (should_include_bool == NULL) {
                        goto error;
                    }
                    should_include = (should_include_bool == Py_True);
                    Py_DECREF(should_include_bool);
                    if (PyDict_SetItem(self->should_trace_cache, tracename, should_include ? disposition : Py_None) < 0) {
                        goto error;
                    }
                }
                else {
                    should_include = (included != Py_None);
                }
                if (!should_include) {
                    tracename = Py_None;
                }
            }
        }
    }
    else {
        tracename = Py_None;
    }

    if (tracename != Py_None) {
        PyObject * file_data = PyDict_GetItem(self->data, tracename);

        if (file_data == NULL) {
            if (PyErr_Occurred()) {
                goto error;
            }
            file_data = PySet_New(NULL);
            if (file_data == NULL) {
                goto error;
            }
            ret2 = PyDict_SetItem(self->data, tracename, file_data);
            if (ret2 < 0) {
                goto error;
            }

            /* If the disposition mentions a plugin, record that. */
            if (file_tracer != Py_None) {
                ret2 = PyDict_SetItem(self->file_tracers, tracename, plugin_name);
                if (ret2 < 0) {
                    goto error;
                }
            }
        }
        else {
            /* PyDict_GetItem gives a borrowed reference. Own it. */
            Py_INCREF(file_data);
        }

        Py_XDECREF(self->pcur_entry->file_data);
        self->pcur_entry->file_data = file_data;
        self->pcur_entry->file_tracer = file_tracer;

        SHOWLOG(PyFrame_GetLineNumber(frame), filename, "traced");
    }
    else {
        Py_XDECREF(self->pcur_entry->file_data);
        self->pcur_entry->file_data = NULL;
        self->pcur_entry->file_tracer = Py_None;
        SHOWLOG(PyFrame_GetLineNumber(frame), filename, "skipped");
    }

    self->pcur_entry->disposition = disposition;

    /* Make the frame right in case settrace(gettrace()) happens. */
    Py_INCREF(self);
    Py_XSETREF(frame->f_trace, (PyObject*)self);

    /* A call event is really a "start frame" event, and can happen for
     * re-entering a generator also.  f_lasti is -1 for a true call, and a
     * real byte offset for a generator re-entry.
     */
    if (frame->f_lasti < 0) {
        self->pcur_entry->last_line = -MyFrame_GetCode(frame)->co_firstlineno;
    }
    else {
        self->pcur_entry->last_line = PyFrame_GetLineNumber(frame);
    }

ok:
    ret = RET_OK;

error:
    Py_XDECREF(next_tracename);
    Py_XDECREF(disposition);
    Py_XDECREF(plugin);
    Py_XDECREF(plugin_name);

    return ret;
}


static void
CTracer_disable_plugin(CTracer *self, PyObject * disposition)
{
    PyObject * ret;
    PyErr_Print();

    STATS( self->stats.pycalls++; )
    ret = PyObject_CallFunctionObjArgs(self->disable_plugin, disposition, NULL);
    if (ret == NULL) {
        goto error;
    }
    Py_DECREF(ret);

    return;

error:
    /* This function doesn't return a status, so if an error happens, print it,
     * but don't interrupt the flow. */
    /* PySys_WriteStderr is nicer, but is not in the public API. */
    fprintf(stderr, "Error occurred while disabling plug-in:\n");
    PyErr_Print();
}


static int
CTracer_unpack_pair(CTracer *self, PyObject *pair, int *p_one, int *p_two)
{
    int ret = RET_ERROR;
    int the_int;
    PyObject * pyint = NULL;
    int index;

    if (!PyTuple_Check(pair) || PyTuple_Size(pair) != 2) {
        PyErr_SetString(
            PyExc_TypeError,
            "line_number_range must return 2-tuple"
            );
        goto error;
    }

    for (index = 0; index < 2; index++) {
        pyint = PyTuple_GetItem(pair, index);
        if (pyint == NULL) {
            goto error;
        }
        if (pyint_as_int(pyint, &the_int) < 0) {
            goto error;
        }
        *(index == 0 ? p_one : p_two) = the_int;
    }

    ret = RET_OK;

error:
    return ret;
}

static int
CTracer_handle_line(CTracer *self, PyFrameObject *frame)
{
    int ret = RET_ERROR;
    int ret2;

    STATS( self->stats.lines++; )
    if (self->pdata_stack->depth >= 0) {
        SHOWLOG(PyFrame_GetLineNumber(frame), MyFrame_GetCode(frame)->co_filename, "line");
        if (self->pcur_entry->file_data) {
            int lineno_from = -1;
            int lineno_to = -1;

            /* We're tracing in this frame: record something. */
            if (self->pcur_entry->file_tracer != Py_None) {
                PyObject * from_to = NULL;
                STATS( self->stats.pycalls++; )
                from_to = PyObject_CallMethodObjArgs(self->pcur_entry->file_tracer, str_line_number_range, frame, NULL);
                if (from_to == NULL) {
                    CTracer_disable_plugin(self, self->pcur_entry->disposition);
                    goto ok;
                }
                ret2 = CTracer_unpack_pair(self, from_to, &lineno_from, &lineno_to);
                Py_DECREF(from_to);
                if (ret2 < 0) {
                    CTracer_disable_plugin(self, self->pcur_entry->disposition);
                    goto ok;
                }
            }
            else {
                lineno_from = lineno_to = PyFrame_GetLineNumber(frame);
            }

            if (lineno_from != -1) {
                for (; lineno_from <= lineno_to; lineno_from++) {
                    if (self->tracing_arcs) {
                        /* Tracing arcs: key is (last_line,this_line). */
                        if (CTracer_record_pair(self, self->pcur_entry->last_line, lineno_from) < 0) {
                            goto error;
                        }
                    }
                    else {
                        /* Tracing lines: key is simply this_line. */
                        PyObject * this_line = PyLong_FromLong((long)lineno_from);
                        if (this_line == NULL) {
                            goto error;
                        }

                        ret2 = PySet_Add(self->pcur_entry->file_data, this_line);
                        Py_DECREF(this_line);
                        if (ret2 < 0) {
                            goto error;
                        }
                    }

                    self->pcur_entry->last_line = lineno_from;
                }
            }
        }
    }

ok:
    ret = RET_OK;

error:

    return ret;
}

static int
CTracer_handle_return(CTracer *self, PyFrameObject *frame)
{
    int ret = RET_ERROR;

    STATS( self->stats.returns++; )
    /* A near-copy of this code is above in the missing-return handler. */
    if (CTracer_set_pdata_stack(self) < 0) {
        goto error;
    }
    self->pcur_entry = &self->pdata_stack->stack[self->pdata_stack->depth];

    if (self->pdata_stack->depth >= 0) {
        if (self->tracing_arcs && self->pcur_entry->file_data) {
            /* Need to distinguish between RETURN_VALUE and YIELD_VALUE. Read
             * the current bytecode to see what it is.  In unusual circumstances
             * (Cython code), co_code can be the empty string, so range-check
             * f_lasti before reading the byte.
             */
            int bytecode = RETURN_VALUE;
            PyObject * pCode = MyFrame_GetCode(frame)->co_code;
            int lasti = MyFrame_lasti(frame);

            if (lasti < PyBytes_GET_SIZE(pCode)) {
                bytecode = PyBytes_AS_STRING(pCode)[lasti];
            }
            if (bytecode != YIELD_VALUE) {
                int first = MyFrame_GetCode(frame)->co_firstlineno;
                if (CTracer_record_pair(self, self->pcur_entry->last_line, -first) < 0) {
                    goto error;
                }
            }
        }

        /* If this frame started a context, then returning from it ends the context. */
        if (self->pcur_entry->started_context) {
            PyObject * val;
            Py_DECREF(self->context);
            self->context = Py_None;
            Py_INCREF(self->context);
            STATS( self->stats.pycalls++; )

            val = PyObject_CallFunctionObjArgs(self->switch_context, self->context, NULL);
            if (val == NULL) {
                goto error;
            }
            Py_DECREF(val);
        }

        /* Pop the stack. */
        SHOWLOG(PyFrame_GetLineNumber(frame), MyFrame_GetCode(frame)->co_filename, "return");
        self->pdata_stack->depth--;
        self->pcur_entry = &self->pdata_stack->stack[self->pdata_stack->depth];
    }

    ret = RET_OK;

error:

    return ret;
}

static int
CTracer_handle_exception(CTracer *self, PyFrameObject *frame)
{
    /* Some code (Python 2.3, and pyexpat anywhere) fires an exception event
        without a return event.  To detect that, we'll keep a copy of the
        parent frame for an exception event.  If the next event is in that
        frame, then we must have returned without a return event.  We can
        synthesize the missing event then.

        Python itself fixed this problem in 2.4.  Pyexpat still has the bug.
        I've reported the problem with pyexpat as http://bugs.python.org/issue6359 .
        If it gets fixed, this code should still work properly.  Maybe some day
        the bug will be fixed everywhere coverage.py is supported, and we can
        remove this missing-return detection.

        More about this fix: https://nedbatchelder.com/blog/200907/a_nasty_little_bug.html
    */
    STATS( self->stats.exceptions++; )
    self->last_exc_back = frame->f_back;
    self->last_exc_firstlineno = MyFrame_GetCode(frame)->co_firstlineno;

    return RET_OK;
}

/*
 * The Trace Function
 */
static int
CTracer_trace(CTracer *self, PyFrameObject *frame, int what, PyObject *arg_unused)
{
    int ret = RET_ERROR;

    #if DO_NOTHING
    return RET_OK;
    #endif

    if (!self->started) {
        /* If CTracer.stop() has been called from another thread, the tracer
           is still active in the current thread. Let's deactivate ourselves
           now. */
        PyEval_SetTrace(NULL, NULL);
        return RET_OK;
    }

    #if WHAT_LOG || TRACE_LOG
    PyObject * ascii = NULL;
    #endif

    #if WHAT_LOG
    if (what <= (int)(sizeof(what_sym)/sizeof(const char *))) {
        ascii = PyUnicode_AsASCIIString(MyFrame_GetCode(frame)->co_filename);
        printf("%x trace: f:%x %s @ %s %d\n", (int)self, (int)frame, what_sym[what], PyBytes_AS_STRING(ascii), PyFrame_GetLineNumber(frame));
        Py_DECREF(ascii);
    }
    #endif

    #if TRACE_LOG
    ascii = PyUnicode_AsASCIIString(MyFrame_GetCode(frame)->co_filename);
    if (strstr(PyBytes_AS_STRING(ascii), start_file) && PyFrame_GetLineNumber(frame) == start_line) {
        logging = TRUE;
    }
    Py_DECREF(ascii);
    #endif

    /* See below for details on missing-return detection. */
    if (CTracer_check_missing_return(self, frame) < 0) {
        goto error;
    }

    self->activity = TRUE;

    switch (what) {
    case PyTrace_CALL:
        if (CTracer_handle_call(self, frame) < 0) {
            goto error;
        }
        break;

    case PyTrace_RETURN:
        if (CTracer_handle_return(self, frame) < 0) {
            goto error;
        }
        break;

    case PyTrace_LINE:
        if (CTracer_handle_line(self, frame) < 0) {
            goto error;
        }
        break;

    case PyTrace_EXCEPTION:
        if (CTracer_handle_exception(self, frame) < 0) {
            goto error;
        }
        break;

    default:
        STATS( self->stats.others++; )
        break;
    }

    ret = RET_OK;
    goto cleanup;

error:
    STATS( self->stats.errors++; )

cleanup:
    return ret;
}


/*
 * Python has two ways to set the trace function: sys.settrace(fn), which
 * takes a Python callable, and PyEval_SetTrace(func, obj), which takes
 * a C function and a Python object.  The way these work together is that
 * sys.settrace(pyfn) calls PyEval_SetTrace(builtin_func, pyfn), using the
 * Python callable as the object in PyEval_SetTrace.  So sys.gettrace()
 * simply returns the Python object used as the second argument to
 * PyEval_SetTrace.  So sys.gettrace() will return our self parameter, which
 * means it must be callable to be used in sys.settrace().
 *
 * So we make ourself callable, equivalent to invoking our trace function.
 *
 * To help with the process of replaying stored frames, this function has an
 * optional keyword argument:
 *
 *      def CTracer_call(frame, event, arg, lineno=0)
 *
 * If provided, the lineno argument is used as the line number, and the
 * frame's f_lineno member is ignored.
 */
static PyObject *
CTracer_call(CTracer *self, PyObject *args, PyObject *kwds)
{
    PyFrameObject *frame;
    PyObject *what_str;
    PyObject *arg;
    int lineno = 0;
    int what;
    int orig_lineno;
    PyObject *ret = NULL;
    PyObject * ascii = NULL;

    #if DO_NOTHING
    CRASH
    #endif

    static char *what_names[] = {
        "call", "exception", "line", "return",
        "c_call", "c_exception", "c_return",
        NULL
        };

    static char *kwlist[] = {"frame", "event", "arg", "lineno", NULL};

    if (!PyArg_ParseTupleAndKeywords(args, kwds, "O!O!O|i:Tracer_call", kwlist,
            &PyFrame_Type, &frame, &PyUnicode_Type, &what_str, &arg, &lineno)) {
        goto done;
    }

    /* In Python, the what argument is a string, we need to find an int
       for the C function. */
    for (what = 0; what_names[what]; what++) {
        int should_break;
        ascii = PyUnicode_AsASCIIString(what_str);
        should_break = !strcmp(PyBytes_AS_STRING(ascii), what_names[what]);
        Py_DECREF(ascii);
        if (should_break) {
            break;
        }
    }

    #if WHAT_LOG
    ascii = PyUnicode_AsASCIIString(MyFrame_GetCode(frame)->co_filename);
    printf("pytrace: %s @ %s %d\n", what_sym[what], PyBytes_AS_STRING(ascii), PyFrame_GetLineNumber(frame));
    Py_DECREF(ascii);
    #endif

    /* Save off the frame's lineno, and use the forced one, if provided. */
    orig_lineno = frame->f_lineno;
    if (lineno > 0) {
        frame->f_lineno = lineno;
    }

    /* Invoke the C function, and return ourselves. */
    if (CTracer_trace(self, frame, what, arg) == RET_OK) {
        Py_INCREF(self);
        ret = (PyObject *)self;
    }

    /* Clean up. */
    frame->f_lineno = orig_lineno;

    /* For better speed, install ourselves the C way so that future calls go
       directly to CTracer_trace, without this intermediate function.

       Only do this if this is a CALL event, since new trace functions only
       take effect then.  If we don't condition it on CALL, then we'll clobber
       the new trace function before it has a chance to get called.  To
       understand why, there are three internal values to track: frame.f_trace,
       c_tracefunc, and c_traceobj.  They are explained here:
       https://nedbatchelder.com/text/trace-function.html

       Without the conditional on PyTrace_CALL, this is what happens:

            def func():                 #   f_trace         c_tracefunc     c_traceobj
                                        #   --------------  --------------  --------------
                                        #   CTracer         CTracer.trace   CTracer
                sys.settrace(my_func)
                                        #   CTracer         trampoline      my_func
                        # Now Python calls trampoline(CTracer), which calls this function
                        # which calls PyEval_SetTrace below, setting us as the tracer again:
                                        #   CTracer         CTracer.trace   CTracer
                        # and it's as if the settrace never happened.
        */
    if (what == PyTrace_CALL) {
        PyEval_SetTrace((Py_tracefunc)CTracer_trace, (PyObject*)self);
    }

done:
    return ret;
}

static PyObject *
CTracer_start(CTracer *self, PyObject *args_unused)
{
    PyEval_SetTrace((Py_tracefunc)CTracer_trace, (PyObject*)self);
    self->started = TRUE;
    self->tracing_arcs = self->trace_arcs && PyObject_IsTrue(self->trace_arcs);

    /* start() returns a trace function usable with sys.settrace() */
    Py_INCREF(self);
    return (PyObject *)self;
}

static PyObject *
CTracer_stop(CTracer *self, PyObject *args_unused)
{
    if (self->started) {
        /* Set the started flag only. The actual call to
           PyEval_SetTrace(NULL, NULL) is delegated to the callback
           itself to ensure that it called from the right thread.
           */
        self->started = FALSE;
    }

    Py_RETURN_NONE;
}

static PyObject *
CTracer_activity(CTracer *self, PyObject *args_unused)
{
    if (self->activity) {
        Py_RETURN_TRUE;
    }
    else {
        Py_RETURN_FALSE;
    }
}

static PyObject *
CTracer_reset_activity(CTracer *self, PyObject *args_unused)
{
    self->activity = FALSE;
    Py_RETURN_NONE;
}

static PyObject *
CTracer_get_stats(CTracer *self, PyObject *args_unused)
{
#if COLLECT_STATS
    return Py_BuildValue(
        "{sI,sI,sI,sI,sI,sI,sI,sI,si,sI,sI,sI}",
        "calls", self->stats.calls,
        "lines", self->stats.lines,
        "returns", self->stats.returns,
        "exceptions", self->stats.exceptions,
        "others", self->stats.others,
        "files", self->stats.files,
        "missed_returns", self->stats.missed_returns,
        "stack_reallocs", self->stats.stack_reallocs,
        "stack_alloc", self->pdata_stack->alloc,
        "errors", self->stats.errors,
        "pycalls", self->stats.pycalls,
        "start_context_calls", self->stats.start_context_calls
        );
#else
    Py_RETURN_NONE;
#endif /* COLLECT_STATS */
}

static PyMemberDef
CTracer_members[] = {
    { "should_trace",       T_OBJECT, offsetof(CTracer, should_trace), 0,
            PyDoc_STR("Function indicating whether to trace a file.") },

    { "check_include",      T_OBJECT, offsetof(CTracer, check_include), 0,
            PyDoc_STR("Function indicating whether to include a file.") },

    { "warn",               T_OBJECT, offsetof(CTracer, warn), 0,
            PyDoc_STR("Function for issuing warnings.") },

    { "concur_id_func",     T_OBJECT, offsetof(CTracer, concur_id_func), 0,
            PyDoc_STR("Function for determining concurrency context") },

    { "data",               T_OBJECT, offsetof(CTracer, data), 0,
            PyDoc_STR("The raw dictionary of trace data.") },

    { "file_tracers",       T_OBJECT, offsetof(CTracer, file_tracers), 0,
            PyDoc_STR("Mapping from file name to plugin name.") },

    { "should_trace_cache", T_OBJECT, offsetof(CTracer, should_trace_cache), 0,
            PyDoc_STR("Dictionary caching should_trace results.") },

    { "trace_arcs",         T_OBJECT, offsetof(CTracer, trace_arcs), 0,
            PyDoc_STR("Should we trace arcs, or just lines?") },

    { "should_start_context", T_OBJECT, offsetof(CTracer, should_start_context), 0,
            PyDoc_STR("Function for starting contexts.") },

    { "switch_context",     T_OBJECT, offsetof(CTracer, switch_context), 0,
            PyDoc_STR("Function for switching to a new context.") },

    { "disable_plugin",     T_OBJECT, offsetof(CTracer, disable_plugin), 0,
            PyDoc_STR("Function for disabling a plugin.") },

    { NULL }
};

static PyMethodDef
CTracer_methods[] = {
    { "start",      (PyCFunction) CTracer_start,        METH_VARARGS,
            PyDoc_STR("Start the tracer") },

    { "stop",       (PyCFunction) CTracer_stop,         METH_VARARGS,
            PyDoc_STR("Stop the tracer") },

    { "get_stats",  (PyCFunction) CTracer_get_stats,    METH_VARARGS,
            PyDoc_STR("Get statistics about the tracing") },

    { "activity",   (PyCFunction) CTracer_activity,     METH_VARARGS,
            PyDoc_STR("Has there been any activity?") },

    { "reset_activity", (PyCFunction) CTracer_reset_activity, METH_VARARGS,
            PyDoc_STR("Reset the activity flag") },

    { NULL }
};

PyTypeObject
CTracerType = {
    PyVarObject_HEAD_INIT(NULL, 0)
    "coverage.CTracer",        /*tp_name*/
    sizeof(CTracer),           /*tp_basicsize*/
    0,                         /*tp_itemsize*/
    (destructor)CTracer_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 */
    (ternaryfunc)CTracer_call, /*tp_call*/
    0,                         /*tp_str*/
    0,                         /*tp_getattro*/
    0,                         /*tp_setattro*/
    0,                         /*tp_as_buffer*/
    Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE, /*tp_flags*/
    "CTracer objects",         /* tp_doc */
    0,                         /* tp_traverse */
    0,                         /* tp_clear */
    0,                         /* tp_richcompare */
    0,                         /* tp_weaklistoffset */
    0,                         /* tp_iter */
    0,                         /* tp_iternext */
    CTracer_methods,           /* tp_methods */
    CTracer_members,           /* tp_members */
    0,                         /* tp_getset */
    0,                         /* tp_base */
    0,                         /* tp_dict */
    0,                         /* tp_descr_get */
    0,                         /* tp_descr_set */
    0,                         /* tp_dictoffset */
    (initproc)CTracer_init,    /* tp_init */
    0,                         /* tp_alloc */
    0,                         /* tp_new */
};