Added FixedArrayOutputIterator and use it for logging without heap allocations.

source/mijin/logging/logger.hpp

@@ -12,6 +12,7 @@
 #include <vector>
 #include "../internal/common.hpp"
 #include "../util/annot.hpp"
+#include "../util/iterators.hpp"
 
 namespace mijin
 {
@@ -148,11 +149,8 @@ public:
     {}
 
     BaseLogger(const BaseLogger&) = default;
-
     BaseLogger(BaseLogger&&) = default;
-
     BaseLogger& operator=(const BaseLogger&) = default;
-
     BaseLogger& operator=(BaseLogger&&) = default;
 
     void addSink(sink_t& sink)
@@ -191,12 +189,28 @@ public:
 
     template<typename... TArgs>
     void log(const level_t& level, const channel_t& channel, std::source_location sourceLocation,
-             std::basic_format_string<char_t, std::type_identity_t<TArgs>...> fmt, TArgs&& ... args) const
+             std::basic_format_string<char_t, std::type_identity_t<TArgs>...> fmt, TArgs&& ... args) const MIJIN_NOEXCEPT
-             MIJIN_NOEXCEPT_IF(noexcept(std::declval<allocator_t>().allocate(1)))
     {
-        string_t buffer(allocator_t(mSinks.get_allocator()));
+        // TODO: make the logger use a traits struct to make this adjustable
-        std::format_to(std::back_inserter(buffer), fmt, std::forward<TArgs>(args)...);
+        static constexpr std::size_t BUFFER_SIZE = 256;
-        log(level, channel, std::move(sourceLocation), buffer.c_str());
+        std::array<char_t, BUFFER_SIZE> buffer;
+
+        // first try to write into a buffer on the stack
+        FixedArrayOutputIterator itAfter = std::format_to(FixedArrayOutputIterator(buffer), fmt, std::forward<TArgs>(args)...);
+        *itAfter = '\0';
+        ++itAfter;
+        if (!itAfter.didOverflow())
+        {
+            log(level, channel, std::move(sourceLocation), buffer.data());
+            return;
+        }
+
+        // if that didn't work, allocate more space
+        const std::size_t newBufferSize = itAfter.getCounter();
+        char_t* newBuffer = static_cast<char_t*>(alloca(newBufferSize * sizeof(char_t)));
+        const std::format_to_n_result result = std::format_to_n(newBuffer, newBufferSize - 1, fmt, std::forward<TArgs>(args)...);
+        *result.out = '\0';
+        log(level, channel, std::move(sourceLocation), newBuffer);
     }
 };
 

source/mijin/util/iterators.hpp

@@ -13,6 +13,7 @@
 #include <variant>
 #include "../container/optional.hpp"
 #include "../internal/common.hpp"
+#include "../util/annot.hpp"
 
 namespace mijin
 {
@@ -855,6 +856,64 @@ TAs collect(TIterable&& iterable)
     return TAs(iterable.begin(), iterable.end());
 }
 
+template<typename TEle, std::size_t numEles>
+class FixedArrayOutputIterator
+{
+public:
+    using array_t = std::array<TEle, numEles>;
+    using difference_type = std::ptrdiff_t;
+    using value_type = TEle;
+    using pointer = value_type*;
+    using reference = value_type&;
+
+    static constexpr std::size_t NUM_ELES = numEles;
+private:
+    not_null_t<array_t*> array_;
+    std::size_t counter_ = 0;
+public:
+    constexpr explicit FixedArrayOutputIterator(array_t& array) MIJIN_NOEXCEPT : array_(&array) {}
+    constexpr explicit FixedArrayOutputIterator(array_t& array, array_t::iterator pos) MIJIN_NOEXCEPT
+            : array_(&array), counter_(static_cast<std::size_t>(pos - array.begin())) {}
+    constexpr FixedArrayOutputIterator(const FixedArrayOutputIterator&) noexcept = default;
+
+    constexpr FixedArrayOutputIterator& operator=(const FixedArrayOutputIterator&) noexcept = default;
+
+    [[nodiscard]]
+    constexpr std::size_t getCounter() const MIJIN_NOEXCEPT
+    {
+        return counter_;
+    }
+
+    [[nodiscard]]
+    constexpr bool didOverflow() const MIJIN_NOEXCEPT
+    {
+        return counter_ >= NUM_ELES;
+    }
+
+    constexpr reference operator*() const MIJIN_NOEXCEPT
+    {
+        static TEle dummy_; // returned when we're at the end of the array
+        if (counter_ < NUM_ELES) {
+            return array_->at(counter_);
+        }
+        return dummy_;
+    }
+
+    constexpr FixedArrayOutputIterator& operator++() MIJIN_NOEXCEPT
+    {
+        ++counter_;
+        return *this;
+    }
+
+    constexpr FixedArrayOutputIterator operator++(int) const MIJIN_NOEXCEPT
+    {
+        FixedArrayOutputIterator copy(*this);
+        ++copy;
+        return copy;
+    }
+};
+static_assert(std::output_iterator<FixedArrayOutputIterator<int, 1>, int>);
+
 namespace pipe
 {
 template<typename T>
@@ -973,7 +1032,7 @@ auto operator|(TIterable&& iterable, Xth<idx>)
 {
     return map(std::forward<TIterable>(iterable), [](auto&& element) { return std::get<idx>(element); } );
 }
-}
+} // namespace pipe
 } // namespace mijin
 
 #endif // MIJIN_UTIL_ITERATORS_HPP_INCLUDED