From: Jérémie Galarneau <jeremie.galarneau@efficios.com>
Date: Tue, 21 Jun 2022 20:46:29 +0000 (-0400)
Subject: consumerd: rename `data_read` to `has_data_left_to_be_read_before_teardown`
X-Git-Url: https://git.lttng.org./?a=commitdiff_plain;h=c715ddc950bf653d9456d92c6ead2e3cbd3c54ae;p=lttng-tools.git

consumerd: rename `data_read` to `has_data_left_to_be_read_before_teardown`

Document the sequence of events after a stream hangs up and rename
the `data_read` stream attribute to give it a more specific name.

Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>
Change-Id: Id7d26fa04fc0d2f0875dced18b6a3f6a7fe7d139
---

diff --git a/src/common/consumer/consumer.cpp b/src/common/consumer/consumer.cpp
index ae8469ea2..8326a8e39 100644
--- a/src/common/consumer/consumer.cpp
+++ b/src/common/consumer/consumer.cpp
@@ -2713,7 +2713,7 @@ void *consumer_thread_data_poll(void *data)
 					consumer_del_stream(local_stream[i], data_ht);
 					local_stream[i] = NULL;
 				} else if (len > 0) {
-					local_stream[i]->data_read = 1;
+					local_stream[i]->has_data_left_to_be_read_before_teardown = 1;
 				}
 			}
 		}
@@ -2744,7 +2744,7 @@ void *consumer_thread_data_poll(void *data)
 					consumer_del_stream(local_stream[i], data_ht);
 					local_stream[i] = NULL;
 				} else if (len > 0) {
-					local_stream[i]->data_read = 1;
+					local_stream[i]->has_data_left_to_be_read_before_teardown = 1;
 				}
 			}
 		}
@@ -2764,37 +2764,45 @@ void *consumer_thread_data_poll(void *data)
 						pollfd[i].fd);
 				lttng_ustconsumer_on_stream_hangup(local_stream[i]);
 				/* Attempt read again, for the data we just flushed. */
-				local_stream[i]->data_read = 1;
+				local_stream[i]->has_data_left_to_be_read_before_teardown = 1;
 			}
 			/*
+			 * When a stream's pipe dies (hup/err/nval), an "inactive producer" flush is
+			 * performed. This type of flush ensures that a new packet is produced no
+			 * matter the consumed/produced positions are.
+			 *
+			 * This, in turn, causes the next pass to see that data available for the
+			 * stream. When we come back here, we can be assured that all available
+			 * data has been consumed and we can finally destroy the stream.
+			 *
 			 * If the poll flag is HUP/ERR/NVAL and we have
 			 * read no data in this pass, we can remove the
 			 * stream from its hash table.
 			 */
 			if ((pollfd[i].revents & POLLHUP)) {
 				DBG("Polling fd %d tells it has hung up.", pollfd[i].fd);
-				if (!local_stream[i]->data_read) {
+				if (!local_stream[i]->has_data_left_to_be_read_before_teardown) {
 					consumer_del_stream(local_stream[i], data_ht);
 					local_stream[i] = NULL;
 					num_hup++;
 				}
 			} else if (pollfd[i].revents & POLLERR) {
 				ERR("Error returned in polling fd %d.", pollfd[i].fd);
-				if (!local_stream[i]->data_read) {
+				if (!local_stream[i]->has_data_left_to_be_read_before_teardown) {
 					consumer_del_stream(local_stream[i], data_ht);
 					local_stream[i] = NULL;
 					num_hup++;
 				}
 			} else if (pollfd[i].revents & POLLNVAL) {
 				ERR("Polling fd %d tells fd is not open.", pollfd[i].fd);
-				if (!local_stream[i]->data_read) {
+				if (!local_stream[i]->has_data_left_to_be_read_before_teardown) {
 					consumer_del_stream(local_stream[i], data_ht);
 					local_stream[i] = NULL;
 					num_hup++;
 				}
 			}
 			if (local_stream[i] != NULL) {
-				local_stream[i]->data_read = 0;
+				local_stream[i]->has_data_left_to_be_read_before_teardown = 0;
 			}
 		}
 	}
diff --git a/src/common/consumer/consumer.hpp b/src/common/consumer/consumer.hpp
index 2c16ae1fa..dd8eb40d4 100644
--- a/src/common/consumer/consumer.hpp
+++ b/src/common/consumer/consumer.hpp
@@ -449,7 +449,11 @@ struct lttng_consumer_stream {
 	/* Amount of bytes written to the output */
 	uint64_t output_written;
 	int shm_fd_is_copy;
-	int data_read;
+	/*
+	 * When a stream's pipe is hung up, a final flush is performed (see hangup_flush_done). This
+	 * indicates whether or not the data resulting from this flush is still to be consumed.
+	 */
+	int has_data_left_to_be_read_before_teardown;
 	int hangup_flush_done;
 
 	/*