chore: call debug stacktrace on SIGUSR1 (#2012)

* add macro to install a signal handler that prints the contents of debug stacktrace on SIGUSR1
* add this on regTests

.github/workflows/regression-tests.yml

@@ -28,7 +28,7 @@ jobs:
       - name: Configure & Build
         run: |
           cmake -B ${GITHUB_WORKSPACE}/build -DCMAKE_BUILD_TYPE=${{matrix.build-type}} -GNinja \
-                -DCMAKE_CXX_COMPILER_LAUNCHER=ccache
+                -DCMAKE_CXX_COMPILER_LAUNCHER=ccache -DPRINT_STACKTRACES_ON_SIGNAL=ON
 
           cd ${GITHUB_WORKSPACE}/build  && ninja dragonfly
           pwd

src/server/CMakeLists.txt

@@ -21,8 +21,6 @@ add_library(dfly_transaction db_slice.cc malloc_stats.cc blocking_controller.cc
             serializer_commons.cc journal/serializer.cc journal/executor.cc journal/streamer.cc
             ${TX_LINUX_SRCS} acl/acl_log.cc slowlog.cc
             )
-cxx_link(dfly_transaction dfly_core strings_lib TRDP::fast_float)
-
 
 if (NOT APPLE)
   SET(SEARCH_FILES search/search_family.cc search/doc_index.cc search/doc_accessors.cc)
@@ -44,6 +42,13 @@ add_library(dragonfly_lib engine_shard_set.cc channel_store.cc command_registry.
             cluster/cluster_family.cc acl/user.cc acl/user_registry.cc acl/acl_family.cc
             acl/validator.cc acl/helpers.cc)
 
+cxx_link(dfly_transaction dfly_core strings_lib TRDP::fast_float)
+
+option(PRINT_STACKTRACES_ON_SIGNAL "Enables DF to print all fiber stacktraces on SIGUSR1" OFF)
+
+if (PRINT_STACKTRACES_ON_SIGNAL)
+  target_compile_definitions(dragonfly_lib PRIVATE PRINT_STACKTRACES_ON_SIGNAL)
+endif()
 
 find_library(ZSTD_LIB NAMES libzstd.a libzstdstatic.a zstd NAMES_PER_DIR REQUIRED)
 

src/server/main_service.cc

@@ -19,6 +19,7 @@ extern "C" {
 #include <absl/strings/str_format.h>
 #include <xxhash.h>
 
+#include <csignal>
 #include <filesystem>
 
 #include "base/flags.h"
@@ -647,6 +648,18 @@ Service::Service(ProactorPool* pp)
     exit(1);
   }
 
+#ifdef PRINT_STACKTRACES_ON_SIGNAL
+  LOG(INFO) << "PRINT STACKTRACES REGISTERED";
+  pp_.GetNextProactor()->RegisterSignal({SIGUSR1}, [this](int signal) {
+    LOG(INFO) << "Received " << strsignal(signal);
+    util::fb2::Mutex m;
+    pp_.AwaitFiberOnAll([&m](unsigned index, util::ProactorBase* base) {
+      std::unique_lock lk(m);
+      util::fb2::detail::FiberInterface::PrintAllFiberStackTraces();
+    });
+  });
+#endif
+
   shard_set = new EngineShardSet(pp);
 
   // We support less than 1024 threads and we support less than 1024 shards.

tests/dragonfly/instance.py

@@ -160,6 +160,14 @@ class DflyInstance:
                 proc.terminate()
             proc.communicate(timeout=15)
         except subprocess.TimeoutExpired:
+            # We need to send SIGUSR1 to DF such that it prints the stacktrace
+            proc.send_signal(signal.SIGUSR1)
+            # Then we sleep for 5 seconds such that DF has enough time to print the stacktraces
+            # We can't really synchronize here because SIGTERM and SIGKILL do not block even if
+            # sigaction explicitly blocks other incoming signals until it handles SIGUSR1.
+            # Even worse, on SIGTERM and SIGKILL none of the handlers registered via sigaction
+            # are guranteed to run
+            time.sleep(5)
             logging.debug(f"Unable to kill the process on port {self._port}")
             logging.debug(f"INFO LOGS of DF are:")
             self.print_info_logs_to_debug_log()