session: add "terminate and reset" support for protocol stacks

Implement routines which terminate currently pending decoder operations
and reset internal state (on the C and Python sides) for instances as
well as sessions. This allows to re-use previously created stacks for
new input data.

4 files changed, 105 insertions, 0 deletions

diff --git a/instance.c b/instance.c
index 5281510..6fbdc01 100644
--- a/instance.c
+++ b/instance.c
@@ -1270,6 +1270,70 @@ SRD_PRIV int srd_inst_decode(struct srd_decoder_inst *di,
 	return SRD_OK;
 }
 
+/**
+ * Terminate current decoder work, prepare for re-use on new input data.
+ *
+ * Terminates all decoder operations in the specified decoder instance
+ * and the instances stacked on top of it. Resets internal state such
+ * that the previously constructed stack can process new input data that
+ * is not related to previously processed input data. This avoids the
+ * expensive and complex re-construction of decoder stacks.
+ *
+ * Callers are expected to follow up with start, metadata, and decode
+ * calls like they would for newly constructed decoder stacks.
+ *
+ * @param di The decoder instance to call. Must not be NULL.
+ * @return SRD_OK upon success, a (negative) error code otherwise.
+ * @private
+ */
+SRD_PRIV int srd_inst_terminate_reset(struct srd_decoder_inst *di)
+{
+	PyGILState_STATE gstate;
+	PyObject *py_ret;
+	GSList *l;
+	int ret;
+
+	if (!di)
+		return SRD_ERR_ARG;
+
+	/*
+	 * Request termination and wait for previously initiated
+	 * background operation to finish. Reset internal state, but
+	 * do not start releasing resources yet. This shall result in
+	 * decoders' state just like after creation. This block handles
+	 * the C language library side.
+	 */
+	srd_dbg("Terminating instance %s", di->inst_id);
+	srd_inst_join_decode_thread(di);
+	srd_inst_reset_state(di);
+
+	/*
+	 * Have the Python side's .reset() method executed (if the PD
+	 * implements it). It's assumed that .reset() assigns variables
+	 * very much like __init__() used to do in the past. Thus memory
+	 * that was allocated in previous calls gets released by Python
+	 * as it's not referenced any longer.
+	 */
+	gstate = PyGILState_Ensure();
+	if (PyObject_HasAttrString(di->py_inst, "reset")) {
+		srd_dbg("Calling .reset() of instance %s", di->inst_id);
+		py_ret = PyObject_CallMethod(di->py_inst, "reset", NULL);
+		Py_XDECREF(py_ret);
+	}
+	PyGILState_Release(gstate);
+
+	/*
+	 * Pass the "restart" request to all stacked decoders.
+	 */
+	for (l = di->next_di; l; l = l->next) {
+		ret = srd_inst_terminate_reset(l->data);
+		if (ret != SRD_OK)
+			return ret;
+	}
+
+	return SRD_OK;
+}
+
 /** @private */
 SRD_PRIV void srd_inst_free(struct srd_decoder_inst *di)
 {
diff --git a/libsigrokdecode-internal.h b/libsigrokdecode-internal.h
index eb79287..6fb590c 100644
--- a/libsigrokdecode-internal.h
+++ b/libsigrokdecode-internal.h
@@ -84,6 +84,7 @@ SRD_PRIV int srd_inst_decode(struct srd_decoder_inst *di,
 		uint64_t abs_start_samplenum, uint64_t abs_end_samplenum,
 		const uint8_t *inbuf, uint64_t inbuflen, uint64_t unitsize);
 SRD_PRIV int process_samples_until_condition_match(struct srd_decoder_inst *di, gboolean *found_match);
+SRD_PRIV int srd_inst_terminate_reset(struct srd_decoder_inst *di);
 SRD_PRIV void srd_inst_free(struct srd_decoder_inst *di);
 SRD_PRIV void srd_inst_free_all(struct srd_session *sess);
 
diff --git a/libsigrokdecode.h b/libsigrokdecode.h
index 982ae19..ee610c9 100644
--- a/libsigrokdecode.h
+++ b/libsigrokdecode.h
@@ -330,6 +330,7 @@ SRD_API int srd_session_metadata_set(struct srd_session *sess, int key,
 SRD_API int srd_session_send(struct srd_session *sess,
 		uint64_t abs_start_samplenum, uint64_t abs_end_samplenum,
 		const uint8_t *inbuf, uint64_t inbuflen, uint64_t unitsize);
+SRD_API int srd_session_terminate_reset(struct srd_session *sess);
 SRD_API int srd_session_destroy(struct srd_session *sess);
 SRD_API int srd_pd_output_callback_add(struct srd_session *sess,
 		int output_type, srd_pd_output_callback cb, void *cb_data);
diff --git a/session.c b/session.c
index 0c1ef82..4d794df 100644
--- a/session.c
+++ b/session.c
@@ -298,6 +298,45 @@ SRD_API int srd_session_send(struct srd_session *sess,
 }
 
 /**
+ * Terminate currently executing decoders in a session, reset internal state.
+ *
+ * All decoder instances have their .wait() method terminated, which
+ * shall terminate .decode() as well. Afterwards the decoders' optional
+ * .reset() method gets executed.
+ *
+ * This routine allows callers to abort pending expensive operations,
+ * when they are no longer interested in the decoders' results. Note
+ * that the decoder state is lost and aborted work cannot resume.
+ *
+ * This routine also allows callers to re-use previously created decoder
+ * stacks to process new input data which is not related to previously
+ * processed input data. This avoids the necessity to re-construct the
+ * decoder stack.
+ *
+ * @param sess The session in which to terminate decoders.
+ * @return SRD_OK upon success, a (negative) error code otherwise.
+ *
+ * @since 0.6.0
+ */
+SRD_API int srd_session_terminate_reset(struct srd_session *sess)
+{
+	GSList *d;
+	int ret;
+
+	if (session_is_valid(sess) != SRD_OK) {
+		srd_err("Invalid session.");
+		return SRD_ERR_ARG;
+	}
+
+	for (d = sess->di_list; d; d = d->next) {
+		ret = srd_inst_terminate_reset(d->data);
+		if (ret != SRD_OK)
+			return ret;
+	}
+	return SRD_OK;
+}
+
+/**
  * Destroy a decoding session.
  *
  * All decoder instances and output callbacks are properly released.