Progress reporting: include origins of running actions

For a user, an important information is to know which actions
are currently running and, more importantly, the target that
caused them. To do so, we need a bit of infrastructure.
- We have to keep track of begin and end of running actions,
  as well as the order in which they were started. That has
  to happen efficiently and in a thread-safe way.
- We have to compute and keep the origin map for actions,
  even if we don't serialize the action graph.

1 files changed, 71 insertions, 0 deletions

diff --git a/src/buildtool/progress_reporting/progress.hpp b/src/buildtool/progress_reporting/progress.hpp
new file mode 100644
index 00000000..5940c880
--- /dev/null
+++ b/src/buildtool/progress_reporting/progress.hpp
@@ -0,0 +1,71 @@
+#ifndef INCLUDED_SRC_BUILDTOOL_PROGRESS_REPORTING_PROGRESS_HPP
+#define INCLUDED_SRC_BUILDTOOL_PROGRESS_REPORTING_PROGRESS_HPP
+
+#include <cstdint>
+#include <mutex>
+#include <string>
+#include <unordered_map>
+#include <utility>
+#include <vector>
+
+#include "src/buildtool/build_engine/target_map/configured_target.hpp"
+#include "src/buildtool/logging/logger.hpp"
+
+class Progress {
+  public:
+    [[nodiscard]] static auto Instance() noexcept -> Progress& {
+        static Progress instance{};
+        return instance;
+    }
+
+    void Start(const std::string& id) noexcept {
+        std::unique_lock lock(m_);
+        ++prio_;
+        try {
+            running_.emplace(id, prio_);
+        } catch (...) {
+            Logger::Log(LogLevel::Warning,
+                        "Internal error in progress tracking; progress reports "
+                        "might be incorrect.");
+        }
+    }
+    void Stop(const std::string& id) noexcept {
+        std::unique_lock lock(m_);
+        running_.erase(id);
+    }
+
+    auto Sample() -> std::string {
+        std::unique_lock lock(m_);
+        std::string result;
+        uint64_t started = prio_ + 1;
+        for (auto const& it : running_) {
+            if (it.second < started) {
+                result = it.first;
+                started = it.second;
+            }
+        }
+        return result;
+    }
+
+    // Return a reference to the origin map. It is the responsibility
+    // of the caller to ensure that access happens only happens in a
+    // single-threaded context.
+    auto OriginMap() -> std::unordered_map<
+        std::string,
+        std::vector<
+            std::pair<BuildMaps::Target::ConfiguredTarget, std::size_t>>>& {
+        return origin_map_;
+    }
+
+  private:
+    uint64_t prio_{};
+    std::mutex m_{};
+    std::unordered_map<std::string, uint64_t> running_{};
+    std::unordered_map<
+        std::string,
+        std::vector<
+            std::pair<BuildMaps::Target::ConfiguredTarget, std::size_t>>>
+        origin_map_;
+};
+
+#endif