src/libtracing/main.cc

@@ -0,0 +1,43 @@
+#include "trace-writer.hh"
+#include <fstream>
+#include <iostream>
+
+using namespace nix::tracing;
+class MyInternedRetriever : public InternedRetriever
+{
+    virtual auto getName(InternedName idx) const -> std::string override
+    {
+        return "meow";
+    }
+
+    virtual auto getPos(InternedPos idx, std::string funcName) const -> TracePos override
+    {
+        return TracePos{
+            .fileName = "file.nix",
+            .functionName = "fun",
+            .lineNumber = 12,
+        };
+    }
+
+public:
+
+    virtual ~MyInternedRetriever() = default;
+};
+
+int main(int argc, char **argv)
+{
+    if (argc < 1) {
+        std::cerr << "provide filename pls\n";
+        return 1;
+    }
+    nix::tracing::TraceWriter tw{std::make_unique<MyInternedRetriever>()};
+
+    tw.begin(InternedPos{1}, InternedName{3}, Timestamp{250});
+    tw.end(Timestamp{1235});
+
+    std::ofstream ofs(argv[1]);
+    auto buf = tw.splat();
+    ofs.write(reinterpret_cast<const char *>(buf.data()), buf.size());
+
+    return 0;
+}

src/libtracing/meow/protos/perfetto/trace/perfetto_trace.pbzero.cc

@@ -0,0 +1 @@
+// Intentionally empty (crbug.com/998165)

src/libtracing/meson.build

@@ -0,0 +1,47 @@
+libtracing_sources = files(
+  'trace-writer.cc',
+
+  'protozero_src/field.cc',
+  'protozero_src/gen_field_helpers.cc',
+  'protozero_src/message_arena.cc',
+  'protozero_src/message.cc',
+  'protozero_src/packed_repeated_fields.cc',
+  'protozero_src/proto_decoder.cc',
+  'protozero_src/scattered_heap_buffer.cc',
+  'protozero_src/scattered_stream_null_delegate.cc',
+  'protozero_src/scattered_stream_writer.cc',
+  'protozero_src/static_buffer.cc',
+  'protozero_src/virtual_destructors.cc',
+)
+
+subdir('perfetto/protozero')
+
+libtracing_headers = [
+  protozero_headers,
+  files(
+    'trace-writer.hh',
+  ),
+]
+
+libtracing = library(
+  'lixtracing',
+  libtracing_sources,
+  dependencies : [ ],
+  install : true,
+  # FIXME(Qyriad): is this right?
+  install_rpath : libdir,
+  cpp_args : [ '-DPERFETTO_DISABLE_LOG' ],
+  include_directories : include_directories('./perfetto/base/build_configs/bazel'),
+)
+
+liblixtracing = declare_dependency(
+  include_directories : include_directories('.'),
+  link_with : libtracing,
+)
+
+tracing_test = executable(
+  'lixtracingtest',
+  files('main.cc'),
+  dependencies : [ liblixtracing ],
+  install : false,
+)

src/libtracing/trace-writer.cc

@@ -0,0 +1,190 @@
+#include "meow/protos/perfetto/trace/perfetto_trace.pbzero.h"
+#include "perfetto/protozero/message.h"
+#include "perfetto/protozero/message_handle.h"
+#include "perfetto/protozero/scattered_heap_buffer.h"
+#include "perfetto/protozero/scattered_stream_writer.h"
+#include "trace-writer.hh"
+#include <memory>
+#include <optional>
+#include <unordered_map>
+
+template<>
+struct std::hash<nix::tracing::InternedPos>
+{
+    size_t operator()(const nix::tracing::InternedPos p) const
+    {
+        return std::hash<uint32_t>()(p.key);
+    }
+};
+
+template<>
+struct std::hash<nix::tracing::InternedName>
+{
+    size_t operator()(const nix::tracing::InternedName p) const
+    {
+        return std::hash<uint32_t>()(p.key);
+    }
+};
+
+namespace nix::tracing {
+
+using namespace perfetto::protos::pbzero;
+
+struct ProtoInternedPos
+{
+    uint32_t key;
+
+    explicit ProtoInternedPos(uint32_t key) : key(key) {}
+    ProtoInternedPos() = delete;
+};
+
+struct ProtoInternedName
+{
+    uint32_t key;
+
+    explicit ProtoInternedName(uint32_t key) : key(key) {}
+    ProtoInternedName() = delete;
+};
+
+struct TraceWriter::Impl
+{
+    std::unique_ptr<InternedRetriever> retriever_;
+    protozero::ScatteredHeapBuffer buf_;
+    protozero::ScatteredStreamWriter writer_;
+    protozero::MessageArena arena_;
+
+    Trace trace_;
+    protozero::MessageHandle<Trace> traceHandle_;
+
+    std::unordered_map<InternedPos, ProtoInternedPos> posMap_;
+    uint64_t posIid_ = 1;
+
+    std::unordered_map<InternedName, ProtoInternedName> nameMap_;
+    uint64_t nameIid_ = 1;
+
+    auto getName(InternedName name, std::optional<std::string> &outName) -> ProtoInternedName;
+
+    auto getPos(InternedPos pos, InternedName funcName, std::optional<TracePos> &outPos) -> ProtoInternedPos;
+
+    Impl(std::unique_ptr<InternedRetriever> retriever)
+        : retriever_(std::move(retriever))
+        , writer_(&this->buf_)
+        , traceHandle_(&this->trace_)
+    {
+        buf_.set_writer(&this->writer_);
+        trace_.Reset(&this->writer_, &this->arena_);
+
+        auto p = protozero::MessageHandle<TracePacket>(trace_.add_packet());
+        auto td = protozero::MessageHandle<TrackDescriptor>(p->set_track_descriptor());
+        td->set_name("track");
+        td->set_uuid(1);
+
+        p->set_trusted_packet_sequence_id(1337);
+        p->set_sequence_flags(perfetto_pbzero_enum_TracePacket::SEQ_INCREMENTAL_STATE_CLEARED);
+        p->set_previous_packet_dropped(true);
+        p->set_first_packet_on_sequence(true);
+    }
+};
+
+auto TraceWriter::Impl::getName(InternedName name, std::optional<std::string> &outName) -> ProtoInternedName
+{
+    if (auto it = nameMap_.find(name); it != nameMap_.end()) {
+        // one already there, return it
+        return it->second;
+    } else {
+        auto nameStr = retriever_->getName(name);
+        outName = nameStr;
+
+        auto newIid = ++nameIid_;
+        nameMap_.insert(std::make_pair(name, newIid));
+        return ProtoInternedName(newIid);
+    }
+}
+
+auto TraceWriter::Impl::getPos(InternedPos pos, InternedName funcName, std::optional<TracePos> &outPos) -> ProtoInternedPos
+{
+    if (auto it = posMap_.find(pos); it != posMap_.end()) {
+        // one already there, return it
+        return it->second;
+    } else {
+        auto nameRetrieved = retriever_->getName(funcName);
+        auto posResolved = retriever_->getPos(pos, nameRetrieved);
+        outPos = posResolved;
+
+        auto newIid = ++posIid_;
+        posMap_.insert(std::make_pair(pos, newIid));
+        return ProtoInternedPos(newIid);
+    }
+}
+
+TraceWriter::TraceWriter(std::unique_ptr<InternedRetriever> retriever)
+    : impl_(std::make_unique<Impl>(std::move(retriever)))
+{
+}
+
+TraceWriter::~TraceWriter() = default;
+
+void TraceWriter::begin(InternedPos pos, InternedName name, Timestamp ts)
+{
+
+    std::optional<std::string> nameToIntern;
+    std::optional<TracePos> posToIntern;
+
+    auto nameIid = impl_->getName(name, nameToIntern);
+    auto posIid = impl_->getPos(pos, name, posToIntern);
+
+    auto packet = protozero::MessageHandle<TracePacket>(impl_->trace_.add_packet());
+
+    packet->set_sequence_flags(perfetto_pbzero_enum_TracePacket::SEQ_NEEDS_INCREMENTAL_STATE);
+
+    if (nameToIntern.has_value() || posToIntern.has_value()) {
+        auto internedData = protozero::MessageHandle<InternedData>(packet->set_interned_data());
+
+        if (nameToIntern.has_value()) {
+            auto evName = protozero::MessageHandle<EventName>(internedData->add_event_names());
+            evName->set_name(*nameToIntern);
+            evName->set_iid(nameIid.key);
+        }
+
+        if (posToIntern.has_value()) {
+            auto sourceLoc = protozero::MessageHandle<SourceLocation>(internedData->add_source_locations());
+            sourceLoc->set_iid(posIid.key);
+            sourceLoc->set_file_name(posToIntern->fileName);
+            sourceLoc->set_function_name(posToIntern->functionName);
+            sourceLoc->set_line_number(posToIntern->lineNumber);
+        }
+    }
+
+    packet->set_timestamp(ts.monotonic_nanos);
+    packet->set_trusted_packet_sequence_id(1337);
+    auto te = protozero::MessageHandle<TrackEvent>(packet->set_track_event());
+    te->set_type(perfetto_pbzero_enum_TrackEvent::TYPE_SLICE_BEGIN);
+    te->set_name_iid(nameIid.key);
+    te->set_source_location_iid(posIid.key);
+
+    // TODO: make a real value
+    te->set_track_uuid(1);
+
+    // te->set_name_iid(nameIid.key);
+    // te->set_name("meow");
+    // TODO: te->set_source_location_iid();
+}
+
+void TraceWriter::end(Timestamp ts)
+{
+    protozero::MessageHandle<TracePacket> tp(impl_->trace_.add_packet());
+    tp->set_timestamp(ts.monotonic_nanos);
+    tp->set_trusted_packet_sequence_id(1337);
+
+    protozero::MessageHandle<TrackEvent> te(tp->set_track_event());
+    te->set_type(perfetto_pbzero_enum_TrackEvent::TYPE_SLICE_END);
+    te->set_track_uuid(1);
+}
+
+auto TraceWriter::splat() const -> std::vector<uint8_t>
+{
+    impl_->traceHandle_->Finalize();
+    return impl_->buf_.StitchSlices();
+}
+
+}

src/libtracing/trace-writer.hh

@@ -0,0 +1,67 @@
+#pragma once
+///@file
+
+#include <stddef.h>
+#include <memory>
+#include <stdint.h>
+#include <string>
+#include <utility>
+#include <vector>
+
+namespace nix::tracing {
+
+struct InternedPos
+{
+    uint32_t key;
+
+    auto operator<=>(InternedPos const & other) const = default;
+    explicit InternedPos(uint32_t key) : key(key) {}
+};
+
+struct InternedName
+{
+    uint32_t key;
+
+    auto operator<=>(InternedName const & other) const = default;
+    explicit InternedName(uint32_t key) : key(key) {}
+};
+
+struct Timestamp
+{
+    uint64_t monotonic_nanos;
+};
+
+struct TracePos
+{
+    std::string fileName;
+    std::string functionName;
+    uint32_t lineNumber;
+};
+
+/** Abstract class that retrieves information about things if they are not
+ * memoized already */
+struct InternedRetriever
+{
+    virtual auto getName(InternedName idx) const -> std::string = 0;
+    virtual auto getPos(InternedPos idx, std::string funcName) const -> TracePos = 0;
+
+    virtual ~InternedRetriever() = default;
+};
+
+class TraceWriter
+{
+    struct Impl;
+    std::unique_ptr<Impl> impl_;
+public:
+    TraceWriter(std::unique_ptr<InternedRetriever> retriever);
+
+    void begin(InternedPos pos, InternedName name, Timestamp ts);
+    void end(Timestamp ts);
+
+    /** Splats the trace out into a buffer */
+    auto splat() const -> std::vector<uint8_t>;
+
+    ~TraceWriter();
+};
+
+}

src/meson.build

@@ -5,6 +5,8 @@ subdir('libutil')
 subdir('libstore')
 # libfetchers depends on libstore
 subdir('libfetchers')
+# libtracing is self-contained
+subdir('libtracing')
 # libexpr depends on all of the above
 subdir('libexpr')
 # libmain depends on libutil and libstore