added basic log file handler

common/log.h

@@ -1,39 +1,57 @@
 #pragma once
 
+#ifndef _GNU_SOURCE
+#define _GNU_SOURCE
+#endif
+
 #include <chrono>
+#include <atomic>
+#include <cstring>
 
 // Specifies a log target.
-//  default simply prints log to stderr
+//  default uses log_handler() with "llama.log" log file
 //  this can be changed, by defining LOG_TARGET
 //  like so:
 //
 //  #define LOG_TARGET (a valid FILE*)
 //  #include "log.h"
 //
-//  The log target can also be redirected to a function
+//  or it can be simply redirected to stdout or stderr
 //  like so:
 //
-//  #define LOG_TARGET log_handler()
+//  #define LOG_TARGET stderr
 //  #include "log.h"
 //
-//  FILE* log_handler()
+//  The log target can also be redirected to a diffrent function
+//  like so:
+//
+//  #define LOG_TARGET log_handler_diffrent()
+//  #include "log.h"
+//
+//  FILE* log_handler_diffrent()
 //  {
 //      return stderr;
 //  }
 //
 //  or:
 //
-//  #define LOG_TARGET log_handler("somelog.log")
+//  #define LOG_TARGET log_handler_another_one("somelog.log")
 //  #include "log.h"
 //
-//  FILE* log_handler(char*filename)
+//  FILE* log_handler_another_one(char*filename)
 //  {
+//      static FILE* logfile = nullptr;
 //      (...)
-//      return fopen(...)
+//      if( !logfile )
+//      {
+//          fopen(...)
+//      }
+//      (...)
+//      return logfile
 //  }
 //
 #ifndef LOG_TARGET
-#define LOG_TARGET stderr
+#define LOG_TARGET log_handler()
 #endif
 
 // Allows disabling timestamps.
@@ -75,4 +93,57 @@
 // This us a trick to bypass the silly
 // "warning: ISO C++11 requires at least one argument for the "..." in a variadic macro"
 // so we xan gave a single macro which can be called just like printf.
-#define LOG(...) _LOG(__VA_ARGS__, '\n')
+#define LOG(...) _LOG(__VA_ARGS__, '\n')
+
+inline FILE *log_handler(std::string s = "llama.log")
+{
+    static std::atomic_bool _initialized{false};
+    static std::atomic_bool _logfileopened{false};
+
+    static FILE* logfile = nullptr;
+
+    if (_initialized)[[likely]]
+    {
+        // with fallback in case something went wrong
+        return logfile ? logfile : stderr;
+    }
+    else
+    {
+        // Mutex-less threadsafe synchronisation.
+        //  we need to make sure not more than one invocation of this function
+        //  attempts to open a file at once.
+        //  compare_exchange_strong checks and updates a flag
+        //  in a single atomic operation.
+        bool expected{false};
+        if( _logfileopened.compare_exchange_strong(expected,true) )
+        {
+            // If the flag was previously false, and we managed to turn it true
+            //  ew are now responsible for opening the log file
+            logfile = fopen( s.c_str(), "wa" );
+
+            if( !logfile )
+            {
+                // Verify whether the file was opened, otherwise fallback to stderr
+                logfile = stderr;
+
+                fprintf(stderr, "Failed to open logfile '%s' with error '%s'\n", s.c_str(), std::strerror(errno));
+                fflush(stderr);
+            }
+
+            _initialized.store(true);
+        }
+        else
+        {
+            // We are not first to open the log file
+            //
+            //  TODO: Better thread-safe option, possibly std::condition_variable
+
+            return stderr;
+        }
+
+        // with fallback in case something went wrong
+        return logfile ? logfile : stderr;
+    }
+
+    return stderr;
+}

examples/main/main.cpp

@@ -3,7 +3,7 @@
 #define _GNU_SOURCE
 #endif
 
-#define LOG_TARGET log_handler("asd")
+//#define LOG_TARGET log_handler("asd")
 //#define LOG_NO_TIMESTAMPS
 #include "common.h"
 
@@ -58,19 +58,6 @@ void sigint_handler(int signo) {
 }
 #endif
 
-inline FILE *log_handler(std::string s)
-{
-    static bool initialized{false};
-
-    if (!initialized)[[unlikely]]
-    {
-        fprintf(stderr,"arg: %s", s.c_str());
-        initialized=true;
-    }
-
-    return stderr;
-}
-
 int main(int argc, char ** argv) {
     gpt_params params;