logd: add a SerializedLogBuffer suitable for compression
Initial commit for a SerializedLogBuffer. The intention here is for
the serialized data to be compressed (currently using zlib) to allow
for substantially longer logs in the same memory footprint.
Test: unit tests
Change-Id: I2528e4e1ff1cf3bc91130173a107f371f04d911a
diff --git a/logd/SerializedFlushToState.h b/logd/SerializedFlushToState.h
new file mode 100644
index 0000000..74b3de5
--- /dev/null
+++ b/logd/SerializedFlushToState.h
@@ -0,0 +1,101 @@
+/*
+ * Copyright (C) 2020 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#pragma once
+
+#include <bitset>
+#include <list>
+#include <queue>
+
+#include "LogBuffer.h"
+#include "SerializedLogChunk.h"
+#include "SerializedLogEntry.h"
+
+struct LogPosition {
+ std::list<SerializedLogChunk>::iterator buffer_it;
+ int read_offset;
+};
+
+struct MinHeapElement {
+ MinHeapElement(log_id_t log_id, const SerializedLogEntry* entry)
+ : log_id(log_id), entry(entry) {}
+ log_id_t log_id;
+ const SerializedLogEntry* entry;
+ // The change of comparison operators is intentional, std::priority_queue uses operator<() to
+ // compare but creates a max heap. Since we want a min heap, we return the opposite result.
+ bool operator<(const MinHeapElement& rhs) const {
+ return entry->sequence() > rhs.entry->sequence();
+ }
+};
+
+// This class tracks the specific point where a FlushTo client has read through the logs. It
+// directly references the std::list<> iterators from the parent SerializedLogBuffer and the offset
+// into each log chunk where it has last read. All interactions with this class, except for its
+// construction, must be done with SerializedLogBuffer::lock_ held. No log chunks that it
+// references may be pruned, which is handled by ensuring prune does not touch any log chunk with
+// highest sequence number greater or equal to start().
+class SerializedFlushToState : public FlushToState {
+ public:
+ // Initializes this state object. For each log buffer set in log_mask, this sets
+ // logs_needed_from_next_position_.
+ SerializedFlushToState(uint64_t start, LogMask log_mask);
+
+ // Decrease the reference of all referenced logs. This happens when a reader is disconnected.
+ ~SerializedFlushToState() override;
+
+ // We can't hold SerializedLogBuffer::lock_ in the constructor, so we must initialize logs here.
+ void InitializeLogs(std::list<SerializedLogChunk>* logs) {
+ if (logs_ == nullptr) logs_ = logs;
+ }
+
+ // Checks to see if any log buffers set in logs_needed_from_next_position_ have new logs and
+ // calls AddMinHeapEntry() if so.
+ void CheckForNewLogs();
+
+ bool HasUnreadLogs() { return !min_heap_.empty(); }
+
+ // Pops the next unread log from the min heap. Add the next log for that log_id to the min heap
+ // if one is available otherwise set logs_needed_from_next_position_ to indicate that we're
+ // waiting for more logs.
+ MinHeapElement PopNextUnreadLog();
+
+ // If the parent log buffer prunes logs, the reference that this class contains may become
+ // invalid, so this must be called first to drop the reference to buffer_it, if any.
+ void Prune(log_id_t log_id, const std::list<SerializedLogChunk>::iterator& buffer_it);
+
+ private:
+ // If there is a log in the serialized log buffer for `log_id` at the read_offset, add it to the
+ // min heap for reading, otherwise set logs_needed_from_next_position_ to indicate that we're
+ // waiting for the next log.
+ void AddMinHeapEntry(log_id_t log_id);
+
+ // Create a LogPosition object for the given log_id by searching through the log chunks for the
+ // first chunk and then first log entry within that chunk that is greater or equal to start().
+ void CreateLogPosition(log_id_t log_id);
+
+ std::list<SerializedLogChunk>* logs_ = nullptr;
+ // An optional structure that contains an iterator to the serialized log buffer and offset into
+ // it that this logger should handle next.
+ std::optional<LogPosition> log_positions_[LOG_ID_MAX];
+ // A bit for each log that is set if a given log_id has no logs or if this client has read all
+ // of its logs. In order words: `logs_[i].empty() || (buffer_it == std::prev(logs_.end) &&
+ // next_log_position == logs_write_position_)`. These will be re-checked in each
+ // loop in case new logs came in.
+ std::bitset<LOG_ID_MAX> logs_needed_from_next_position_ = {};
+ // A min heap that has up to one entry per log buffer, sorted by sequence number, of the next
+ // element that this reader should read.
+ std::priority_queue<MinHeapElement> min_heap_;
+};