TimeCheck: Use FixedString
Avoids unnecessary malloc when constructing strings.
Test: simpleperf using Oboetester
Test: atest mediautils_fixedstring_tests
Bug: 238654698
Merged-In: I6b5239a0599de0cd0a60c55d9120e5bfaab7e6b9
Change-Id: I6b5239a0599de0cd0a60c55d9120e5bfaab7e6b9
(cherry picked from commit 35f9615b0299672a51e02884847dfa0800bfc9f4)
diff --git a/media/utils/include/mediautils/FixedString.h b/media/utils/include/mediautils/FixedString.h
new file mode 100644
index 0000000..047aa82
--- /dev/null
+++ b/media/utils/include/mediautils/FixedString.h
@@ -0,0 +1,282 @@
+/*
+ * Copyright (C) 2022 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 <algorithm>
+#include <string>
+#include <string_view>
+
+namespace android::mediautils {
+
+/*
+ * FixedString is a stack allocatable string buffer that supports
+ * simple appending of other strings and string_views.
+ *
+ * It is designed for no-malloc operation when std::string
+ * small buffer optimization is insufficient.
+ *
+ * To keep code small, use asStringView() for operations on this.
+ *
+ * Notes:
+ * 1) Appending beyond the internal buffer size results in truncation.
+ *
+ * Alternatives:
+ * 1) If you want a sharable copy-on-write string implementation,
+ * consider using the legacy android::String8().
+ * 2) Using std::string with a fixed stack allocator may suit your needs,
+ * but exception avoidance is tricky.
+ * 3) Using C++20 ranges https://en.cppreference.com/w/cpp/ranges if you don't
+ * need backing store. Be careful about allocation with ranges.
+ *
+ * Good small sizes are multiples of 16 minus 2, e.g. 14, 30, 46, 62.
+ *
+ * Implementation Notes:
+ * 1) No iterators or [] for FixedString - please convert to std::string_view.
+ * 2) For small N (e.g. less than 62), consider a change to always zero fill and
+ * potentially prevent always zero terminating (if one only does append).
+ *
+ * Possible arguments to create/append:
+ * 1) A FixedString.
+ * 2) A single char.
+ * 3) A char * pointer.
+ * 4) A std::string.
+ * 5) A std::string_view (or something convertible to it).
+ *
+ * Example:
+ *
+ * FixedString s1(std::string("a")); // ctor
+ * s1 << "bc" << 'd' << '\n'; // streaming append
+ * s1 += "hello"; // += append
+ * ASSERT_EQ(s1, "abcd\nhello");
+ */
+template <uint32_t N>
+struct FixedString
+{
+ // Find the best size type.
+ using strsize_t = std::conditional_t<(N > 255), uint32_t, uint8_t>;
+
+ // constructors
+ FixedString() { // override default
+ buffer_[0] = '\0';
+ }
+
+ FixedString(const FixedString& other) { // override default.
+ copyFrom<N>(other);
+ }
+
+ // The following constructor is not explicit to allow
+ // FixedString<8> s = "abcd";
+ template <typename ...Types>
+ FixedString(Types&&... args) {
+ append(std::forward<Types>(args)...);
+ }
+
+ // copy assign (copyFrom checks for equality and returns *this).
+ FixedString& operator=(const FixedString& other) { // override default.
+ return copyFrom<N>(other);
+ }
+
+ template <typename ...Types>
+ FixedString& operator=(Types&&... args) {
+ size_ = 0;
+ return append(std::forward<Types>(args)...);
+ }
+
+ // operator equals
+ bool operator==(const char *s) const {
+ return strncmp(c_str(), s, capacity() + 1) == 0;
+ }
+
+ bool operator==(std::string_view s) const {
+ return size() == s.size() && memcmp(data(), s.data(), size()) == 0;
+ }
+
+ // operator not-equals
+ template <typename T>
+ bool operator!=(const T& other) const {
+ return !operator==(other);
+ }
+
+ // operator +=
+ template <typename ...Types>
+ FixedString& operator+=(Types&&... args) {
+ return append(std::forward<Types>(args)...);
+ }
+
+ // conversion to std::string_view.
+ operator std::string_view() const {
+ return asStringView();
+ }
+
+ // basic observers
+ size_t buffer_offset() const { return offsetof(std::decay_t<decltype(*this)>, buffer_); }
+ static constexpr uint32_t capacity() { return N; }
+ uint32_t size() const { return size_; }
+ uint32_t remaining() const { return size_ >= N ? 0 : N - size_; }
+ bool empty() const { return size_ == 0; }
+ bool full() const { return size_ == N; } // when full, possible truncation risk.
+ char * data() { return buffer_; }
+ const char * data() const { return buffer_; }
+ const char * c_str() const { return buffer_; }
+
+ inline std::string_view asStringView() const {
+ return { buffer_, static_cast<size_t>(size_) };
+ }
+ inline std::string asString() const {
+ return { buffer_, static_cast<size_t>(size_) };
+ }
+
+ void clear() { size_ = 0; buffer_[0] = 0; }
+
+ // Implementation of append - using templates
+ // to guarantee precedence in the presence of ambiguity.
+ //
+ // Consider C++20 template overloading through constraints and concepts.
+ template <typename T>
+ FixedString& append(const T& t) {
+ using decayT = std::decay_t<T>;
+ if constexpr (is_specialization_v<decayT, FixedString>) {
+ // A FixedString<U>
+ if (size_ == 0) {
+ // optimization to erase everything.
+ return copyFrom(t);
+ } else {
+ return appendStringView({t.data(), t.size()});
+ }
+ } else if constexpr(std::is_same_v<decayT, char>) {
+ if (size_ < N) {
+ buffer_[size_++] = t;
+ buffer_[size_] = '\0';
+ }
+ return *this;
+ } else if constexpr(std::is_same_v<decayT, char *>) {
+ // Some char* ptr.
+ return appendString(t);
+ } else if constexpr (std::is_convertible_v<decayT, std::string_view>) {
+ // std::string_view, std::string, or some other convertible type.
+ return appendStringView(t);
+ } else /* constexpr */ {
+ static_assert(dependent_false_v<T>, "non-matching append type");
+ }
+ }
+
+ FixedString& appendStringView(std::string_view s) {
+ uint32_t total = std::min(static_cast<size_t>(N - size_), s.size());
+ memcpy(buffer_ + size_, s.data(), total);
+ size_ += total;
+ buffer_[size_] = '\0';
+ return *this;
+ }
+
+ FixedString& appendString(const char *s) {
+ // strncpy zero pads to the end,
+ // strlcpy returns total expected length,
+ // we don't have strncpy_s in Bionic,
+ // so we write our own here.
+ while (size_ < N && *s != '\0') {
+ buffer_[size_++] = *s++;
+ }
+ buffer_[size_] = '\0';
+ return *this;
+ }
+
+ // Copy initialize the struct.
+ // Note: We are POD but customize the copying for acceleration
+ // of moving small strings embedded in a large buffers.
+ template <uint32_t U>
+ FixedString& copyFrom(const FixedString<U>& other) {
+ if ((void*)this != (void*)&other) { // not a self-assignment
+ if (other.size() == 0) {
+ size_ = 0;
+ buffer_[0] = '\0';
+ return *this;
+ }
+ constexpr size_t kSizeToCopyWhole = 64;
+ if constexpr (N == U &&
+ sizeof(*this) == sizeof(other) &&
+ sizeof(*this) <= kSizeToCopyWhole) {
+ // As we have the same str size type, we can just
+ // memcpy with fixed size, which can be easily optimized.
+ memcpy(static_cast<void*>(this), static_cast<const void*>(&other), sizeof(*this));
+ return *this;
+ }
+ if constexpr (std::is_same_v<strsize_t, typename FixedString<U>::strsize_t>) {
+ constexpr size_t kAlign = 8; // align to a multiple of 8.
+ static_assert((kAlign & (kAlign - 1)) == 0); // power of 2.
+ // we check any alignment issues.
+ if (buffer_offset() == other.buffer_offset() && other.size() <= capacity()) {
+ // improve on standard POD copying by reducing size.
+ const size_t mincpy = buffer_offset() + other.size() + 1 /* nul */;
+ const size_t maxcpy = std::min(sizeof(*this), sizeof(other));
+ const size_t cpysize = std::min(mincpy + kAlign - 1 & ~(kAlign - 1), maxcpy);
+ memcpy(static_cast<void*>(this), static_cast<const void*>(&other), cpysize);
+ return *this;
+ }
+ }
+ size_ = std::min(other.size(), capacity());
+ memcpy(buffer_, other.data(), size_);
+ buffer_[size_] = '\0'; // zero terminate.
+ }
+ return *this;
+ }
+
+private:
+ // Template helper methods
+
+ template <typename Test, template <uint32_t> class Ref>
+ struct is_specialization : std::false_type {};
+
+ template <template <uint32_t> class Ref, uint32_t UU>
+ struct is_specialization<Ref<UU>, Ref>: std::true_type {};
+
+ template <typename Test, template <uint32_t> class Ref>
+ static inline constexpr bool is_specialization_v = is_specialization<Test, Ref>::value;
+
+ // For static assert(false) we need a template version to avoid early failure.
+ template <typename T>
+ static inline constexpr bool dependent_false_v = false;
+
+ // POD variables
+ strsize_t size_ = 0;
+ char buffer_[N + 1 /* allow zero termination */];
+};
+
+// Stream operator syntactic sugar.
+// Example:
+// s << 'b' << "c" << "d" << '\n';
+template <uint32_t N, typename ...Types>
+FixedString<N>& operator<<(FixedString<N>& fs, Types&&... args) {
+ return fs.append(std::forward<Types>(args)...);
+}
+
+// We do not use a default size for fixed string as changing
+// the default size would lead to different behavior - we want the
+// size to be explicitly known.
+
+// FixedString62 of 62 chars fits in one typical cache line.
+using FixedString62 = FixedString<62>;
+
+// Slightly smaller
+using FixedString30 = FixedString<30>;
+
+// Since we have added copy and assignment optimizations,
+// we are no longer trivially assignable and copyable.
+// But we check standard layout here to prevent inclusion of unacceptable members or virtuals.
+static_assert(std::is_standard_layout_v<FixedString62>);
+static_assert(std::is_standard_layout_v<FixedString30>);
+
+} // namespace android::mediautils
diff --git a/media/utils/include/mediautils/TimeCheck.h b/media/utils/include/mediautils/TimeCheck.h
index ef03aef..038e7dd 100644
--- a/media/utils/include/mediautils/TimeCheck.h
+++ b/media/utils/include/mediautils/TimeCheck.h
@@ -60,7 +60,7 @@
* the TimeCheck object is destroyed or leaves scope.
* \param crashOnTimeout true if the object issues an abort on timeout.
*/
- explicit TimeCheck(std::string tag, OnTimerFunc&& onTimer = {},
+ explicit TimeCheck(std::string_view tag, OnTimerFunc&& onTimer = {},
uint32_t timeoutMs = kDefaultTimeOutMs, bool crashOnTimeout = true);
TimeCheck() = default;
@@ -79,7 +79,17 @@
// The usage here is const safe.
class TimeCheckHandler {
public:
- const std::string tag;
+ template <typename S, typename F>
+ TimeCheckHandler(S&& _tag, F&& _onTimer, bool _crashOnTimeout,
+ const std::chrono::system_clock::time_point& _startTime,
+ pid_t _tid)
+ : tag(std::forward<S>(_tag))
+ , onTimer(std::forward<F>(_onTimer))
+ , crashOnTimeout(_crashOnTimeout)
+ , startTime(_startTime)
+ , tid(_tid)
+ {}
+ const FixedString62 tag;
const OnTimerFunc onTimer;
const bool crashOnTimeout;
const std::chrono::system_clock::time_point startTime;
diff --git a/media/utils/include/mediautils/TimerThread.h b/media/utils/include/mediautils/TimerThread.h
index ffee602..349bffd 100644
--- a/media/utils/include/mediautils/TimerThread.h
+++ b/media/utils/include/mediautils/TimerThread.h
@@ -27,6 +27,8 @@
#include <android-base/thread_annotations.h>
+#include <mediautils/FixedString.h>
+
namespace android::mediautils {
/**
@@ -54,7 +56,7 @@
* \returns a handle that can be used for cancellation.
*/
Handle scheduleTask(
- std::string tag, std::function<void()>&& func, std::chrono::milliseconds timeout);
+ std::string_view tag, std::function<void()>&& func, std::chrono::milliseconds timeout);
/**
* Tracks a task that shows up on toString() until cancelled.
@@ -62,7 +64,7 @@
* \param tag string associated with the task.
* \returns a handle that can be used for cancellation.
*/
- Handle trackTask(std::string tag);
+ Handle trackTask(std::string_view tag);
/**
* Cancels a task previously scheduled with scheduleTask()
@@ -129,12 +131,22 @@
// To minimize movement of data, we pass around shared_ptrs to Requests.
// These are allocated and deallocated outside of the lock.
struct Request {
+ Request(const std::chrono::system_clock::time_point& _scheduled,
+ const std::chrono::system_clock::time_point& _deadline,
+ pid_t _tid,
+ std::string_view _tag)
+ : scheduled(_scheduled)
+ , deadline(_deadline)
+ , tid(_tid)
+ , tag(_tag)
+ {}
+
const std::chrono::system_clock::time_point scheduled;
const std::chrono::system_clock::time_point deadline; // deadline := scheduled + timeout
// if deadline == scheduled, no
// timeout, task not executed.
const pid_t tid;
- const std::string tag;
+ const FixedString62 tag;
std::string toString() const;
};