feat(logging): add CerrLogger std::cerr backend (3/6)

Third block: the first concrete sink, and the process default until the spdlog
backend lands.

- CerrLogger writes to std::cerr with a fixed line layout
  `YYYY-MM-DDThh:mm:ss.mmmZ LEVEL [tid] file:line] message`. Timestamps use UTC
  std::chrono floored to milliseconds (no gmtime/localtime -- thread-unsafe);
  the thread id is the OS-native id, cached per thread.
- Level is a std::atomic<LogLevel>; a mutex guards the whole formatted-line write
  so concurrent lines never interleave. Log()/Flush() wrap stream ops in
  try/catch so the noexcept contract holds even if the stream throws.
- MakeDefaultLogger() now returns CerrLogger.

Wired into both builds and installed; cerr_logger_test covers layout, level
filtering, and concurrent-write safety.

Co-authored-by: Isaac

Author: kamcheungting-db

src/iceberg/CMakeLists.txt

@@ -49,6 +49,7 @@ set(ICEBERG_SOURCES
     inheritable_metadata.cc
     json_serde.cc
     location_provider.cc
+    logging/cerr_logger.cc
     logging/logger.cc
     manifest/manifest_adapter.cc
     manifest/manifest_entry.cc

src/iceberg/logging/cerr_logger.cc

@@ -0,0 +1,106 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you 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.
+ */
+
+#include "iceberg/logging/cerr_logger.h"
+
+#include <chrono>
+#include <cstdint>
+#include <format>
+#include <iostream>
+#include <mutex>
+#include <string>
+#include <string_view>
+
+#if defined(_WIN32)
+#  include <windows.h>
+#elif defined(__APPLE__)
+#  include <pthread.h>
+#else
+#  include <unistd.h>
+
+#  include <sys/syscall.h>
+#endif
+
+namespace iceberg {
+
+namespace {
+
+/// \brief OS-native thread id, cached per thread to avoid a syscall per log.
+///
+/// Matches the cross-process-correlatable id used by spdlog/glog (not the opaque
+/// std::thread::id), and avoids the std::formatter<std::thread::id> (P2693)
+/// minimum-toolchain dependency.
+uint64_t OsThreadId() noexcept {
+  static thread_local uint64_t tid = []() -> uint64_t {
+#if defined(_WIN32)
+    return static_cast<uint64_t>(::GetCurrentThreadId());
+#elif defined(__APPLE__)
+    uint64_t id = 0;
+    pthread_threadid_np(nullptr, &id);
+    return id;
+#else
+    return static_cast<uint64_t>(::syscall(SYS_gettid));
+#endif
+  }();
+  return tid;
+}
+
+/// \brief Trailing path component of a source file path.
+std::string_view Basename(std::string_view path) noexcept {
+  auto pos = path.find_last_of("/\\");
+  return pos == std::string_view::npos ? path : path.substr(pos + 1);
+}
+
+/// \brief Format a record into a single newline-terminated line.
+std::string FormatLine(const LogMessage& message) {
+  auto now =
+      std::chrono::floor<std::chrono::milliseconds>(std::chrono::system_clock::now());
+  return std::format("{:%Y-%m-%dT%H:%M:%S}Z {} [{}] {}:{}] {}\n", now,
+                     ToString(message.level), OsThreadId(),
+                     Basename(message.location.file_name()), message.location.line(),
+                     message.message);
+}
+
+}  // namespace
+
+void CerrLogger::Log(LogMessage&& message) noexcept {
+  try {
+    std::string line = FormatLine(message);
+    std::lock_guard<std::mutex> lock(mutex_);
+    std::cerr << line;
+  } catch (...) {
+    // Logging must never throw. Reached if either formatting or the write fails;
+    // emit a short marker best-effort and swallow anything further.
+    try {
+      std::lock_guard<std::mutex> lock(mutex_);
+      std::cerr << "<fmt error>\n";
+    } catch (...) {
+    }
+  }
+}
+
+void CerrLogger::Flush() noexcept {
+  try {
+    std::lock_guard<std::mutex> lock(mutex_);
+    std::cerr.flush();
+  } catch (...) {
+  }
+}
+
+}  // namespace iceberg

src/iceberg/logging/cerr_logger.h

@@ -0,0 +1,61 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you 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
+
+/// \file iceberg/logging/cerr_logger.h
+/// \brief Always-available std::cerr logging backend.
+
+#include <atomic>
+#include <mutex>
+
+#include "iceberg/iceberg_export.h"
+#include "iceberg/logging/log_level.h"
+#include "iceberg/logging/logger.h"
+
+namespace iceberg {
+
+/// \brief Logger that writes one line per record to std::cerr.
+///
+/// Line layout: `YYYY-MM-DDThh:mm:ss.mmmZ LEVEL [tid] file:line] message`.
+/// The minimum level is held in a lock-free atomic; a mutex serializes the
+/// whole-line write so concurrent records never interleave. Pure standard
+/// library -- always compiled, regardless of ICEBERG_SPDLOG.
+class ICEBERG_EXPORT CerrLogger : public Logger {
+ public:
+  explicit CerrLogger(LogLevel level = LogLevel::kInfo) : level_(level) {}
+
+  bool ShouldLog(LogLevel level) const noexcept override {
+    return level >= level_.load(std::memory_order_relaxed);
+  }
+  void Log(LogMessage&& message) noexcept override;
+  void SetLevel(LogLevel level) noexcept override {
+    level_.store(level, std::memory_order_relaxed);
+  }
+  LogLevel level() const noexcept override {
+    return level_.load(std::memory_order_relaxed);
+  }
+  void Flush() noexcept override;
+
+ private:
+  std::atomic<LogLevel> level_;
+  std::mutex mutex_;
+};
+
+}  // namespace iceberg

src/iceberg/logging/logger.cc

@@ -26,6 +26,8 @@
 #include <tuple>
 #include <utility>
 
+#include "iceberg/logging/cerr_logger.h"
+
 namespace iceberg {
 
 namespace {
@@ -42,10 +44,9 @@ class NoopLogger final : public Logger {
 
 /// \brief Construct the process default logger for this build configuration.
 ///
-/// This block ships only the interface and the no-op logger; the concrete
-/// std::cerr and spdlog sinks (and the build-config selection between them)
-/// arrive in later blocks, which update this factory.
-std::shared_ptr<Logger> MakeDefaultLogger() { return std::make_shared<NoopLogger>(); }
+/// Uses the always-available std::cerr sink. The spdlog backend (preferred when
+/// compiled in) is wired into this factory in a later block.
+std::shared_ptr<Logger> MakeDefaultLogger() { return std::make_shared<CerrLogger>(); }
 
 /// \brief The process-global default-logger slot.
 struct DefaultSlot {

src/iceberg/logging/meson.build

@@ -15,4 +15,7 @@
 # specific language governing permissions and limitations
 # under the License.
 
-install_headers(['log_level.h', 'logger.h'], subdir: 'iceberg/logging')
+install_headers(
+    ['cerr_logger.h', 'log_level.h', 'logger.h'],
+    subdir: 'iceberg/logging',
+)

src/iceberg/meson.build

@@ -74,6 +74,7 @@ iceberg_sources = files(
     'inspect/snapshots_table.cc',
     'json_serde.cc',
     'location_provider.cc',
+    'logging/cerr_logger.cc',
     'logging/logger.cc',
     'manifest/manifest_adapter.cc',
     'manifest/manifest_entry.cc',

src/iceberg/test/CMakeLists.txt

@@ -102,7 +102,11 @@ add_iceberg_test(table_test
                  table_test.cc
                  table_update_test.cc)
 
-add_iceberg_test(logging_test SOURCES log_level_test.cc logger_test.cc)
+add_iceberg_test(logging_test
+                 SOURCES
+                 cerr_logger_test.cc
+                 log_level_test.cc
+                 logger_test.cc)
 
 add_iceberg_test(expression_test
                  SOURCES