Making message print thread safe to prevent output mangling

lib/message.cc

@@ -40,6 +40,8 @@
 #include <unistd.h>
 #include <sys/time.h>
 
+#include <mutex>
+
 #define BACKTRACE_ON_PANIC 1
 #if BACKTRACE_ON_PANIC
 #include <execinfo.h>
@@ -48,6 +50,8 @@
 #define TIMESTAMP_BASE62 0
 #define TIMESTAMP_NUMERIC 1
 
+std::mutex mtx;
+
 void __attribute__((weak))
 Message_VA(enum Message_Type type,
            const char *fname, int line, const char *func,
@@ -74,6 +78,9 @@ _Message_VA(enum Message_Type type, FILE *fp,
             const char *fname, int line, const char *func,
             const char *fmt, va_list args)
 {
+    // Lock mutex to make sure the output is not mangled.
+    mtx.lock();
+
     static int haveColor = -1;
     struct msg_desc {
         const char *prefix;
@@ -150,6 +157,9 @@ _Message_VA(enum Message_Type type, FILE *fp,
         fputs("\033[0m", fp);
     fprintf(fp, "\n");
     fflush(fp);
+
+    // Unlock mutex.
+    mtx.unlock();
 }
 
 void _Panic(void)