Merge #16112: util: Log early messages

faa2a47cd7 logging: Add threadsafety comments (MarcoFalke)
0b282f9b00 Log early messages with -printtoconsole (Anthony Towns)
412987430c Replace OpenDebugLog() with StartLogging() (Anthony Towns)

Pull request description:

  Early log messages are dropped on the floor and they'd never make it to the console or debug log. This can be tested by running the test included in this pull request without re-compiling the `bitcoind`.

  Fix that by buffering early messages and flushing them as soon as all logging options have been initialized and logging has been started.

  This pull request is identical to  "Log early messages with -printtoconsole" (#13088)  by **ajtowns**, with the following changes:
  * Rebased
  * Added docstrings for `m_buffering` and `StartLogging`
  * Switch `CCriticalSection` (aka `RecursiveMutex`) to just `Mutex` in the last commit
  * Added tests

  Fixes #16098
  Fixes #13157
  Closes #13088

ACKs for commit faa2a4:
  ajtowns:
    utACK faa2a47cd7bcdbd187035c76f8dbd0442f6818dc
  hebasto:
    ACK faa2a47cd7bcdbd187035c76f8dbd0442f6818dc
  kristapsk:
    ACK faa2a47cd7bcdbd187035c76f8dbd0442f6818dc (ran added functional test before / after recompiling, didn't do additional testing)

Tree-SHA512: 685e2882642fe2a43ce171d42862582dadb840d03cda8236a994322c389ca2a1f3f431b179b2726c155c61793543bb340c568a5455d97f8b83bc7d307a85d387

4 files changed, 63 insertions, 41 deletions

diff --git a/src/init.cpp b/src/init.cpp
index 2a10f28a84..6625080c6e 100644
--- a/src/init.cpp
+++ b/src/init.cpp
@@ -852,12 +852,6 @@ void InitLogging()
 {
     LogInstance().m_print_to_file = !gArgs.IsArgNegated("-debuglogfile");
     LogInstance().m_file_path = AbsPathForConfigVal(gArgs.GetArg("-debuglogfile", DEFAULT_DEBUGLOGFILE));
-
-    // Add newlines to the logfile to distinguish this execution from the last
-    // one; called before console logging is set up, so this is only sent to
-    // debug.log.
-    LogPrintf("\n\n\n\n\n");
-
     LogInstance().m_print_to_console = gArgs.GetBoolArg("-printtoconsole", !gArgs.GetBoolArg("-daemon", false));
     LogInstance().m_log_timestamps = gArgs.GetBoolArg("-logtimestamps", DEFAULT_LOGTIMESTAMPS);
     LogInstance().m_log_time_micros = gArgs.GetBoolArg("-logtimemicros", DEFAULT_LOGTIMEMICROS);
@@ -1237,10 +1231,10 @@ bool AppInitMain(InitInterfaces& interfaces)
             // and because this needs to happen before any other debug.log printing
             LogInstance().ShrinkDebugFile();
         }
-        if (!LogInstance().OpenDebugLog()) {
+    }
+    if (!LogInstance().StartLogging()) {
             return InitError(strprintf("Could not open debug log file %s",
                 LogInstance().m_file_path.string()));
-        }
     }
 
     if (!LogInstance().m_log_timestamps)
diff --git a/src/logging.cpp b/src/logging.cpp
index 3eda4995db..418a701179 100644
--- a/src/logging.cpp
+++ b/src/logging.cpp
@@ -39,24 +39,38 @@ static int FileWriteStr(const std::string &str, FILE *fp)
     return fwrite(str.data(), 1, str.size(), fp);
 }
 
-bool BCLog::Logger::OpenDebugLog()
+bool BCLog::Logger::StartLogging()
 {
-    std::lock_guard<std::mutex> scoped_lock(m_file_mutex);
+    std::lock_guard<std::mutex> scoped_lock(m_cs);
 
+    assert(m_buffering);
     assert(m_fileout == nullptr);
-    assert(!m_file_path.empty());
 
-    m_fileout = fsbridge::fopen(m_file_path, "a");
-    if (!m_fileout) {
-        return false;
+    if (m_print_to_file) {
+        assert(!m_file_path.empty());
+        m_fileout = fsbridge::fopen(m_file_path, "a");
+        if (!m_fileout) {
+            return false;
+        }
+
+        setbuf(m_fileout, nullptr); // unbuffered
+
+        // Add newlines to the logfile to distinguish this execution from the
+        // last one.
+        FileWriteStr("\n\n\n\n\n", m_fileout);
     }
 
-    setbuf(m_fileout, nullptr); // unbuffered
     // dump buffered messages from before we opened the log
+    m_buffering = false;
     while (!m_msgs_before_open.empty()) {
-        FileWriteStr(m_msgs_before_open.front(), m_fileout);
+        const std::string& s = m_msgs_before_open.front();
+
+        if (m_print_to_file) FileWriteStr(s, m_fileout);
+        if (m_print_to_console) fwrite(s.data(), 1, s.size(), stdout);
+
         m_msgs_before_open.pop_front();
     }
+    if (m_print_to_console) fflush(stdout);
 
     return true;
 }
@@ -202,8 +216,9 @@ std::string BCLog::Logger::LogTimestampStr(const std::string& str)
     return strStamped;
 }
 
-void BCLog::Logger::LogPrintStr(const std::string &str)
+void BCLog::Logger::LogPrintStr(const std::string& str)
 {
+    std::lock_guard<std::mutex> scoped_lock(m_cs);
     std::string str_prefixed = str;
 
     if (m_log_threadnames && m_started_new_line) {
@@ -214,32 +229,31 @@ void BCLog::Logger::LogPrintStr(const std::string &str)
 
     m_started_new_line = !str.empty() && str[str.size()-1] == '\n';
 
+    if (m_buffering) {
+        // buffer if we haven't started logging yet
+        m_msgs_before_open.push_back(str_prefixed);
+        return;
+    }
+
     if (m_print_to_console) {
         // print to console
         fwrite(str_prefixed.data(), 1, str_prefixed.size(), stdout);
         fflush(stdout);
     }
     if (m_print_to_file) {
-        std::lock_guard<std::mutex> scoped_lock(m_file_mutex);
-
-        // buffer if we haven't opened the log yet
-        if (m_fileout == nullptr) {
-            m_msgs_before_open.push_back(str_prefixed);
-        }
-        else
-        {
-            // reopen the log file, if requested
-            if (m_reopen_file) {
-                m_reopen_file = false;
-                FILE* new_fileout = fsbridge::fopen(m_file_path, "a");
-                if (new_fileout) {
-                    setbuf(new_fileout, nullptr); // unbuffered
-                    fclose(m_fileout);
-                    m_fileout = new_fileout;
-                }
+        assert(m_fileout != nullptr);
+
+        // reopen the log file, if requested
+        if (m_reopen_file) {
+            m_reopen_file = false;
+            FILE* new_fileout = fsbridge::fopen(m_file_path, "a");
+            if (new_fileout) {
+                setbuf(new_fileout, nullptr); // unbuffered
+                fclose(m_fileout);
+                m_fileout = new_fileout;
             }
-            FileWriteStr(str_prefixed, m_fileout);
         }
+        FileWriteStr(str_prefixed, m_fileout);
     }
 }
 
diff --git a/src/logging.h b/src/logging.h
index e399d4c307..36b1a4045d 100644
--- a/src/logging.h
+++ b/src/logging.h
@@ -60,9 +60,10 @@ namespace BCLog {
     class Logger
     {
     private:
-        FILE* m_fileout = nullptr;
-        std::mutex m_file_mutex;
-        std::list<std::string> m_msgs_before_open;
+        mutable std::mutex m_cs;                   // Can not use Mutex from sync.h because in debug mode it would cause a deadlock when a potential deadlock was detected
+        FILE* m_fileout = nullptr;                 // GUARDED_BY(m_cs)
+        std::list<std::string> m_msgs_before_open; // GUARDED_BY(m_cs)
+        bool m_buffering{true};                    //!< Buffer messages before logging can be started. GUARDED_BY(m_cs)
 
         /**
          * m_started_new_line is a state variable that will suppress printing of
@@ -88,12 +89,18 @@ namespace BCLog {
         std::atomic<bool> m_reopen_file{false};
 
         /** Send a string to the log output */
-        void LogPrintStr(const std::string &str);
+        void LogPrintStr(const std::string& str);
 
         /** Returns whether logs will be written to any output */
-        bool Enabled() const { return m_print_to_console || m_print_to_file; }
+        bool Enabled() const
+        {
+            std::lock_guard<std::mutex> scoped_lock(m_cs);
+            return m_buffering || m_print_to_console || m_print_to_file;
+        }
+
+        /** Start logging (and flush all buffered messages) */
+        bool StartLogging();
 
-        bool OpenDebugLog();
         void ShrinkDebugFile();
 
         uint32_t GetCategoryMask() const { return m_categories.load(); }
diff --git a/test/functional/feature_config_args.py b/test/functional/feature_config_args.py
index 2b93e3c24d..074a832594 100755
--- a/test/functional/feature_config_args.py
+++ b/test/functional/feature_config_args.py
@@ -61,9 +61,16 @@ class ConfArgsTest(BitcoinTestFramework):
         with open(inc_conf_file2_path, 'w', encoding='utf-8') as conf:
             conf.write('')  # clear
 
+    def test_log_buffer(self):
+        with self.nodes[0].assert_debug_log(expected_msgs=['Warning: parsed potentially confusing double-negative -connect=0']):
+            self.start_node(0, extra_args=['-noconnect=0'])
+        self.stop_node(0)
+
     def run_test(self):
         self.stop_node(0)
 
+        self.test_log_buffer()
+
         self.test_config_file_parser()
 
         # Remove the -datadir argument so it doesn't override the config file