Allow to enable shard/cdc debugging at runtime using USR2

cpp/cdc/CDC.cpp

@@ -614,7 +614,7 @@ void runCDC(const std::string& dbDir, const CDCOptions& options) {
         }
         logOut = &fileOut;
     }
-    Logger logger(options.logLevel, *logOut);
+    Logger logger(options.logLevel, *logOut, true);
 
     {
         Env env(logger, "startup");

cpp/core/Env.cpp

@@ -1,5 +1,9 @@
+#include <atomic>
+#include <signal.h>
+
 #include "Env.hpp"
 #include "Assert.hpp"
+#include "Exception.hpp"
 
 std::ostream& operator<<(std::ostream& out, LogLevel ll) {
     switch (ll) {
@@ -20,3 +24,56 @@ std::ostream& operator<<(std::ostream& out, LogLevel ll) {
     }
     return out;
 }
+
+void Logger::toggleDebug() {
+    if (_logLevel == LogLevel::LOG_DEBUG) {
+        _logLevel = _savedLogLevel; 
+    } else {
+        _logLevel = LogLevel::LOG_DEBUG;
+    }
+}
+
+static std::atomic<Logger*> debuggableLogger(nullptr);
+
+extern "C" {
+static void loggerSignalHandler(int signal_number) {
+    (*debuggableLogger).toggleDebug();
+}
+}
+
+void installLoggerSignalHandler(void* logger) {
+    Logger* old = nullptr;
+    if (!debuggableLogger.compare_exchange_strong(old, (Logger*)logger)) {
+        throw EGGS_EXCEPTION("Could not install logger signal handler, some other logger is already here.");
+    }
+
+    struct sigaction act;
+    act.sa_handler = loggerSignalHandler;
+    if (sigemptyset(&act.sa_mask) != 0) {
+        SYSCALL_EXCEPTION("sigemptyset");
+    }
+    act.sa_flags = 0;
+
+    // USR1 is used by undertaker
+    if (sigaction(SIGUSR2, &act, NULL) < 0) {
+        throw SYSCALL_EXCEPTION("sigaction");
+    }
+}
+
+void tearDownLoggerSignalHandler(void* logger) {
+    Logger* old = (Logger*)logger;
+    if (!debuggableLogger.compare_exchange_strong(old, nullptr)) {
+        throw EGGS_EXCEPTION("Could not tear down logger signal handler, bad preexisting logger");
+    }
+
+    struct sigaction act;
+    act.sa_handler = SIG_DFL;
+    if (sigemptyset(&act.sa_mask) != 0) {
+        SYSCALL_EXCEPTION("sigemptyset");
+    }
+    act.sa_flags = 0;
+
+    if (sigaction(SIGUSR2, &act, NULL) < 0) {
+        throw SYSCALL_EXCEPTION("sigaction");
+    }
+}

cpp/core/Env.hpp

@@ -4,8 +4,10 @@
 #include <mutex>
 #include <sstream>
 #include <string>
+#include <signal.h>
 
 #include "Common.hpp"
+#include "Exception.hpp"
 #include "Time.hpp"
 
 enum class LogLevel : uint32_t {
@@ -17,13 +19,25 @@ enum class LogLevel : uint32_t {
 
 std::ostream& operator<<(std::ostream& out, LogLevel ll);
 
+void installLoggerSignalHandler(void* logger);
+void tearDownLoggerSignalHandler(void* logger);
+
 struct Logger {
 private:
     LogLevel _logLevel;
+    LogLevel _savedLogLevel;
     std::ostream& _out;
     std::mutex _mutex;
 public:
-    Logger(LogLevel logLevel, std::ostream& out): _logLevel(logLevel), _out(out) {}
+    Logger(LogLevel logLevel, std::ostream& out, bool usr1ToDebug): _logLevel(logLevel), _savedLogLevel(logLevel), _out(out) {
+        if (usr1ToDebug) {
+            installLoggerSignalHandler(this);
+        }
+    }
+
+    ~Logger() {
+        tearDownLoggerSignalHandler(this);
+    }
 
     template<typename ...Args>
     void _log(LogLevel level, const std::string& prefix, const char* fmt, Args&&... args) {
@@ -45,6 +59,8 @@ public:
         std::scoped_lock lock(_mutex);
         _out.flush();
     }
+
+    void toggleDebug();
 };
 
 struct Env {

cpp/shard/Shard.cpp

@@ -410,7 +410,7 @@ void runShard(ShardId shid, const std::string& dbDir, const ShardOptions& option
         }
         logOut = &fileOut;
     }
-    Logger logger(options.logLevel, *logOut);
+    Logger logger(options.logLevel, *logOut, true);
 
     {
         Env env(logger, "startup");

cpp/tests/tests.cpp

@@ -399,7 +399,7 @@ struct TempShardDB {
     ShardId shid;
     std::unique_ptr<ShardDB> db;
 
-    TempShardDB(LogLevel level, ShardId shid_): logger(level, std::cerr), shid(shid_) {
+    TempShardDB(LogLevel level, ShardId shid_): logger(level, std::cerr, false), shid(shid_) {
         dbDir = std::string("temp-shard-db.XXXXXX");
         if (mkdtemp(dbDir.data()) == nullptr) {
             throw SYSCALL_EXCEPTION("mkdtemp");