Allow multiple logging::LogMessage{Handler,Listener}s

base/logging.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "base/logging.h"
 
 #include <limits.h>
 #include <stdint.h>
 
 #include "base/debug/activity_tracker.h"
@@ skipping 31 matching lines @@
 #include <sys/stat.h>
 #include <unistd.h>
 #define MAX_PATH PATH_MAX
 typedef FILE* FileHandle;
 typedef pthread_mutex_t* MutexHandle;
 #endif
 
 #include <algorithm>
 #include <cstring>
 #include <ctime>
+#include <deque>
 #include <iomanip>
 #include <ostream>
 #include <string>
 
 #include "base/base_switches.h"
 #include "base/command_line.h"
 #include "base/debug/alias.h"
 #include "base/debug/debugger.h"
 #include "base/debug/stack_trace.h"
+#include "base/lazy_instance.h"
 #include "base/posix/eintr_wrapper.h"
 #include "base/strings/string_piece.h"
 #include "base/strings/string_util.h"
 #include "base/strings/stringprintf.h"
 #include "base/strings/sys_string_conversions.h"
 #include "base/strings/utf_string_conversions.h"
 #include "base/synchronization/lock_impl.h"
+#include "base/synchronization/read_write_lock.h"
 #include "base/threading/platform_thread.h"
 #include "base/vlog.h"
 #if defined(OS_POSIX)
 #include "base/posix/safe_strerror.h"
 #endif
 
 #if defined(OS_ANDROID)
 #include <android/log.h>
 #endif
 
@@ skipping 38 matching lines @@
 bool g_log_thread_id = false;
 bool g_log_timestamp = true;
 bool g_log_tickcount = false;
 
 // Should we pop up fatal debug messages in a dialog?
 bool show_error_dialogs = false;
 
 // An assert handler override specified by the client to be called instead of
 // the debug message dialog and process termination.
 LogAssertHandlerFunction log_assert_handler = nullptr;
-// A log message handler that gets notified of every log message we process.
-LogMessageHandlerFunction log_message_handler = nullptr;
+// Log message handlers that get notified of every log message we process.
+base::LazyInstance<std::deque<LogMessageHandler*>>::Leaky log_message_handlers =
+    LAZY_INSTANCE_INITIALIZER;
+base::LazyInstance<base::subtle::ReadWriteLock>::Leaky
+    log_message_handler_lock = LAZY_INSTANCE_INITIALIZER;
+// Log message listeners that get notified of every log message we process
+// before log message handlers.
+base::LazyInstance<std::deque<LogMessageListener*>>::Leaky
+    log_message_listeners = LAZY_INSTANCE_INITIALIZER;
+base::LazyInstance<base::subtle::ReadWriteLock>::Leaky
+    log_message_listener_lock = LAZY_INSTANCE_INITIALIZER;
 
 // Helper functions to wrap platform differences.
 
 int32_t CurrentProcessId() {
 #if defined(OS_WIN)
   return GetCurrentProcessId();
 #elif defined(OS_POSIX)
   return getpid();
 #endif
 }
@@ skipping 197 matching lines @@
 void CloseLogFileUnlocked() {
   if (!g_log_file)
     return;
 
   CloseFile(g_log_file);
   g_log_file = nullptr;
 }
 
 }  // namespace
 
+LogMessageHandler::LogMessageHandler() {
+  base::subtle::AutoWriteLock lock(log_message_handler_lock.Get());
+  log_message_handlers.Get().push_front(this);
+}
+
+LogMessageHandler::~LogMessageHandler() {
+  base::subtle::AutoWriteLock lock(log_message_handler_lock.Get());
+  auto& handlers = log_message_handlers.Get();
+  size_t count = handlers.size();
+  handlers.erase(std::remove(handlers.begin(), handlers.end(), this),
+                 handlers.end());
+  DCHECK_EQ(count - 1, handlers.size());

[grt (UTC plus 2), 2017/01/04 09:12:18]

this check is a bit bogus. if you think it's possible that |this| is not in the
container, then the erase(remove) pattern will provoke undefined behavior or
worse. rationale: if |this| is not in |handlers|, the call to remove() will
return handlers.end(). end, being a "past the end" iterator cannot be
dereferenced. erase() must not be called with a "first" iterator that cannot be
dereferenced. hence, boom if |this| is not in the container.

that aside, you're only removing one element, so erase(remove) shouldn't be any
more efficient than a single erase. so, please pick one of:

  handlers.erase(handlers.find(handlers.begin(), handlers.end(), this));

or:

  auto it = handlers.find(handlers.begin(), handlers.end(), this);
  if (it != handlers.end())
    handlers.erase(it);
  else
    NOTREACHED();

depending on how confident you are that |this| will always be in the container.

+}
+
+size_t LogMessageHandlerCountForTesting() {
+  base::subtle::AutoReadLock lock(log_message_handler_lock.Get());
+  return log_message_handlers.Get().size();
+}
+
+LogMessageListener::LogMessageListener() {
+  base::subtle::AutoWriteLock lock(log_message_listener_lock.Get());
+  log_message_listeners.Get().push_front(this);
+}
+
+LogMessageListener::~LogMessageListener() {
+  base::subtle::AutoWriteLock lock(log_message_listener_lock.Get());
+  auto& listeners = log_message_listeners.Get();
+  size_t count = listeners.size();
+  listeners.erase(std::remove(listeners.begin(), listeners.end(), this),
+                  listeners.end());
+  DCHECK_EQ(count - 1, listeners.size());
+}
+
+size_t LogMessageListenerCountForTesting() {
+  base::subtle::AutoReadLock lock(log_message_listener_lock.Get());
+  return log_message_listeners.Get().size();
+}
+
 // This is never instantiated, it's just used for EAT_STREAM_PARAMETERS to have
 // an object of the correct type on the LHS of the unused part of the ternary
 // operator.
 std::ostream* g_swallow_stream;
 
 LoggingSettings::LoggingSettings()
     : logging_dest(LOG_DEFAULT),
       log_file(nullptr),
       lock_log(LOCK_LOG_FILE),
       delete_old(APPEND_TO_OLD_LOG_FILE) {}
@@ skipping 52 matching lines @@
   return g_min_log_level;
 }
 
 bool ShouldCreateLogMessage(int severity) {
   if (severity < g_min_log_level)
     return false;
 
   // Return true here unless we know ~LogMessage won't do anything. Note that
   // ~LogMessage writes to stderr if severity_ >= kAlwaysPrintErrorLevel, even
   // when g_logging_destination is LOG_NONE.
-  return g_logging_destination != LOG_NONE || log_message_handler ||
-         severity >= kAlwaysPrintErrorLevel;
+  bool handlers_empty, listeners_empty;
+  {
+    base::subtle::AutoReadLock lock(log_message_handler_lock.Get());
+    handlers_empty = log_message_handlers.Get().empty();
+  }
+  {
+    base::subtle::AutoReadLock lock(log_message_listener_lock.Get());
+    listeners_empty = log_message_listeners.Get().empty();
+  }
+  return g_logging_destination != LOG_NONE || !handlers_empty ||
+         !listeners_empty || severity >= kAlwaysPrintErrorLevel;
 }
 
 int GetVlogVerbosity() {
   return std::max(-1, LOG_INFO - GetMinLogLevel());
 }
 
 int GetVlogLevelHelper(const char* file, size_t N) {
   DCHECK_GT(N, 0U);
   // Note: |g_vlog_info| may change on a different thread during startup
   // (but will always be valid or nullptr).
@@ skipping 12 matching lines @@
 }
 
 void SetShowErrorDialogs(bool enable_dialogs) {
   show_error_dialogs = enable_dialogs;
 }
 
 void SetLogAssertHandler(LogAssertHandlerFunction handler) {
   log_assert_handler = handler;
 }
 
-void SetLogMessageHandler(LogMessageHandlerFunction handler) {
-  log_message_handler = handler;
-}
-
-LogMessageHandlerFunction GetLogMessageHandler() {
-  return log_message_handler;
-}
-
 // Explicit instantiations for commonly used comparisons.
 template std::string* MakeCheckOpString<int, int>(
     const int&, const int&, const char* names);
 template std::string* MakeCheckOpString<unsigned long, unsigned long>(
     const unsigned long&, const unsigned long&, const char* names);
 template std::string* MakeCheckOpString<unsigned long, unsigned int>(
     const unsigned long&, const unsigned int&, const char* names);
 template std::string* MakeCheckOpString<unsigned int, unsigned long>(
     const unsigned int&, const unsigned long&, const char* names);
 template std::string* MakeCheckOpString<std::string, std::string>(
@@ skipping 66 matching lines @@
   if (severity_ == LOG_FATAL && !base::debug::BeingDebugged()) {
     // Include a stack trace on a fatal, unless a debugger is attached.
     base::debug::StackTrace trace;
     stream_ << std::endl;  // Newline to separate from log message.
     trace.OutputToStream(&stream_);
   }
 #endif
   stream_ << std::endl;
   std::string str_newline(stream_.str());
 
-  // Give any log message handler first dibs on the message.
-  if (log_message_handler &&
-      log_message_handler(severity_, file_, line_,
-                          message_start_, str_newline)) {
-    // The handler took care of it, no further processing.
-    return;
+  {
+    base::subtle::AutoReadLock lock(log_message_listener_lock.Get());
+    // Broadcast to log message listeners first.
+    for (auto* listener : log_message_listeners.Get()) {
+      listener->OnMessage(severity_, file_, line_, message_start_, str_newline);
+    }
+  }
+
+  {
+    base::subtle::AutoReadLock lock(log_message_handler_lock.Get());
+    // Give log message handlers first dibs on the message.
+    for (auto* handler : log_message_handlers.Get()) {
+      if (handler->OnMessage(severity_, file_, line_, message_start_,
+                             str_newline)) {
+        // The handler took care of it, no further processing.
+        return;
+      }
+    }
   }
 
   if ((g_logging_destination & LOG_TO_SYSTEM_DEBUG_LOG) != 0) {
 #if defined(OS_WIN)
     OutputDebugStringA(str_newline.c_str());
 #elif defined(OS_MACOSX)
     // In LOG_TO_SYSTEM_DEBUG_LOG mode, log messages are always written to
     // stderr. If stderr is /dev/null, also log via ASL (Apple System Log). If
     // there's something weird about stderr, assume that log messages are going
     // nowhere and log via ASL too. Messages logged via ASL show up in
@@ skipping 386 matching lines @@
 BASE_EXPORT void LogErrorNotReached(const char* file, int line) {
   LogMessage(file, line, LOG_ERROR).stream()
       << "NOTREACHED() hit.";
 }
 
 }  // namespace logging
 
 std::ostream& std::operator<<(std::ostream& out, const wchar_t* wstr) {
   return out << (wstr ? base::WideToUTF8(wstr) : std::string());
 }