Add missing concurrency protection in logger (#12325)

src/log.cpp

@@ -152,12 +152,14 @@ void Logger::addOutput(ILogOutput *out)
 
 void Logger::addOutput(ILogOutput *out, LogLevel lev)
 {
+	MutexAutoLock lock(m_mutex);
 	m_outputs[lev].push_back(out);
 	m_has_outputs[lev] = true;
 }
 
 void Logger::addOutputMasked(ILogOutput *out, LogLevelMask mask)
 {
+	MutexAutoLock lock(m_mutex);
 	for (size_t i = 0; i < LL_MAX; i++) {
 		if (mask & LOGLEVEL_TO_MASKLEVEL(i)) {
 			m_outputs[i].push_back(out);
@@ -168,6 +170,7 @@ void Logger::addOutputMasked(ILogOutput *out, LogLevelMask mask)
 
 void Logger::addOutputMaxLevel(ILogOutput *out, LogLevel lev)
 {
+	MutexAutoLock lock(m_mutex);
 	assert(lev < LL_MAX);
 	for (size_t i = 0; i <= lev; i++) {
 		m_outputs[i].push_back(out);
@@ -177,6 +180,7 @@ void Logger::addOutputMaxLevel(ILogOutput *out, LogLevel lev)
 
 LogLevelMask Logger::removeOutput(ILogOutput *out)
 {
+	MutexAutoLock lock(m_mutex);
 	LogLevelMask ret_mask = 0;
 	for (size_t i = 0; i < LL_MAX; i++) {
 		std::vector<ILogOutput *>::iterator it;
@@ -386,6 +390,6 @@ void LogOutputBuffer::logRaw(LogLevel lev, const std::string &line)
 		default: break;
 		}
 	}
-
-	m_buffer.push(color.append(line));
+	MutexAutoLock lock(m_buffer_mutex);
+	m_buffer.emplace(color.append(line));
 }

src/log.h

@@ -29,6 +29,7 @@ with this program; if not, write to the Free Software Foundation, Inc.,
 #if !defined(_WIN32)  // POSIX
 	#include <unistd.h>
 #endif
+#include "threading/mutex_auto_lock.h"
 #include "util/basic_macros.h"
 #include "util/stream.h"
 #include "irrlichttypes.h"
@@ -168,24 +169,31 @@ public:
 
 	void clear()
 	{
+		MutexAutoLock lock(m_buffer_mutex);
 		m_buffer = std::queue<std::string>();
 	}
 
 	bool empty() const
 	{
+		MutexAutoLock lock(m_buffer_mutex);
 		return m_buffer.empty();
 	}
 
 	std::string get()
 	{
-		if (empty())
+		MutexAutoLock lock(m_buffer_mutex);
+		if (m_buffer.empty())
 			return "";
-		std::string s = m_buffer.front();
+		std::string s = std::move(m_buffer.front());
 		m_buffer.pop();
 		return s;
 	}
 
 private:
+	// g_logger serializes calls to logRaw() with a mutex, but that
+	// doesn't prevent get() / clear() from being called on top of it.
+	// This mutex prevents that.
+	mutable std::mutex m_buffer_mutex;
 	std::queue<std::string> m_buffer;
 	Logger &m_logger;
 };