support multiple log message handlers in base/logging.h

base/logging.cc

Index: base/logging.cc
diff --git a/base/logging.cc b/base/logging.cc
index 0771b47c182e5c18c868f1124a0784bf411d74a9..316843bba603ded5ab16c72fcd20c5e2db75789f 100644
--- a/base/logging.cc
+++ b/base/logging.cc
@@ -52,6 +52,7 @@ typedef pthread_mutex_t* MutexHandle;
 #include <iomanip>
 #include <ostream>
 #include <string>
+#include <vector>
 
 #include "base/base_switches.h"
 #include "base/command_line.h"
@@ -123,8 +124,8 @@ 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.
+std::vector<LogMessageHandlerFunction>* log_message_handlers = nullptr;
 
 // Helper functions to wrap platform differences.
 
@@ -409,7 +410,8 @@ bool ShouldCreateLogMessage(int severity) {
   // 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 ||
+  return g_logging_destination != LOG_NONE ||
+         (log_message_handlers && log_message_handlers->size() > 0) ||
          severity >= kAlwaysPrintErrorLevel;
 }
 
@@ -443,12 +445,24 @@ void SetLogAssertHandler(LogAssertHandlerFunction handler) {
   log_assert_handler = handler;
 }
 
-void SetLogMessageHandler(LogMessageHandlerFunction handler) {
-  log_message_handler = handler;
+void AddLogMessageHandler(LogMessageHandlerFunction handler) {
+  if (!log_message_handlers)
+    log_message_handlers = new std::vector<LogMessageHandlerFunction>;
+  DCHECK_EQ(0, std::count(log_message_handlers->begin(),
+                          log_message_handlers->end(), handler));
+  log_message_handlers->push_back(handler);
 }
 
-LogMessageHandlerFunction GetLogMessageHandler() {
-  return log_message_handler;
+void RemoveLogMessageHandler(LogMessageHandlerFunction handler) {
+  if (log_message_handlers) {
+    auto it = std::find(log_message_handlers->begin(),
+                        log_message_handlers->end(), handler);
+    if (it != log_message_handlers->end()) {
+      log_message_handlers->erase(it);
+      return;
+    }
+  }
+  NOTREACHED();
 }
 
 // Explicit instantiations for commonly used comparisons.
@@ -538,11 +552,16 @@ LogMessage::~LogMessage() {
   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;
+  if (log_message_handlers) {
+    const std::string message = str_newline.substr(message_start_);
+    if (std::count_if(log_message_handlers->begin(),
+                      log_message_handlers->end(),
+                      [this, &message](auto handler) {
+                        return handler(severity_, file_, line_, message);
+                      }) > 0) {
+      // At least one of the handlers took care of it, no further processing.
+      return;
+    }
   }
 
   if ((g_logging_destination & LOG_TO_SYSTEM_DEBUG_LOG) != 0) {