Author: Pavel Labath Date: 2024-10-17T17:29:38+02:00 New Revision: 98b419ca7688aa2823df1e87f58051aaa8d9c37f
URL: https://github.com/llvm/llvm-project/commit/98b419ca7688aa2823df1e87f58051aaa8d9c37f DIFF: https://github.com/llvm/llvm-project/commit/98b419ca7688aa2823df1e87f58051aaa8d9c37f.diff LOG: [lldb] Don't exit the main loop when in runs out of things to listen on (#112565) This behavior made sense in the beginning as the class was completely single threaded, so if the source count ever reached zero, there was no way to add new ones. In https://reviews.llvm.org/D131160, the class gained the ability to add events (callbacks) from other threads, which means that is no longer the case (and indeed, one possible use case for this class -- acting as a sort of arbiter for multiple threads wanting to run code while making sure it runs serially -- has this class sit in an empty Run call most of the time). I'm not aware of us having a use for such a thing right now, but one of my tests in another patch turned into something similar by accident. Another problem with the current approach is that, in a distributed/dynamic setup (multiple things using the main loop without a clear coordinator), one can never be sure whether unregistering a specific event will terminate the loop (it depends on whether there are other listeners). We had this problem in lldb-platform.cpp, where we had to add an additional layer of synchronization to avoid premature termination. We can remove this if we can rely on the loop terminating only when we tell it to. Added: Modified: lldb/source/Host/posix/MainLoopPosix.cpp lldb/source/Host/windows/MainLoopWindows.cpp lldb/tools/lldb-server/lldb-platform.cpp lldb/unittests/Host/MainLoopTest.cpp Removed: ################################################################################ diff --git a/lldb/source/Host/posix/MainLoopPosix.cpp b/lldb/source/Host/posix/MainLoopPosix.cpp index 816581e70294a7..6f8eaa55cfdf09 100644 --- a/lldb/source/Host/posix/MainLoopPosix.cpp +++ b/lldb/source/Host/posix/MainLoopPosix.cpp @@ -365,10 +365,7 @@ Status MainLoopPosix::Run() { Status error; RunImpl impl(*this); - // run until termination or until we run out of things to listen to - // (m_read_fds will always contain m_trigger_pipe fd, so check for > 1) - while (!m_terminate_request && - (m_read_fds.size() > 1 || !m_signals.empty())) { + while (!m_terminate_request) { error = impl.Poll(); if (error.Fail()) return error; diff --git a/lldb/source/Host/windows/MainLoopWindows.cpp b/lldb/source/Host/windows/MainLoopWindows.cpp index 88d929535ab6c5..c9aa6d339d8f48 100644 --- a/lldb/source/Host/windows/MainLoopWindows.cpp +++ b/lldb/source/Host/windows/MainLoopWindows.cpp @@ -116,9 +116,7 @@ Status MainLoopWindows::Run() { Status error; - // run until termination or until we run out of things to listen to - while (!m_terminate_request && !m_read_fds.empty()) { - + while (!m_terminate_request) { llvm::Expected<size_t> signaled_event = Poll(); if (!signaled_event) return Status::FromError(signaled_event.takeError()); diff --git a/lldb/tools/lldb-server/lldb-platform.cpp b/lldb/tools/lldb-server/lldb-platform.cpp index 2ef780578d0a28..735a558810da58 100644 --- a/lldb/tools/lldb-server/lldb-platform.cpp +++ b/lldb/tools/lldb-server/lldb-platform.cpp @@ -260,8 +260,7 @@ static void client_handle(GDBRemoteCommunicationServerPlatform &platform, static Status spawn_process(const char *progname, const Socket *conn_socket, uint16_t gdb_port, const lldb_private::Args &args, const std::string &log_file, - const StringRef log_channels, MainLoop &main_loop, - std::promise<void> &child_exited) { + const StringRef log_channels, MainLoop &main_loop) { Status error; SharedSocket shared_socket(conn_socket, error); if (error.Fail()) @@ -301,12 +300,10 @@ static Status spawn_process(const char *progname, const Socket *conn_socket, if (g_server) launch_info.SetMonitorProcessCallback([](lldb::pid_t, int, int) {}); else - launch_info.SetMonitorProcessCallback( - [&child_exited, &main_loop](lldb::pid_t, int, int) { - main_loop.AddPendingCallback( - [](MainLoopBase &loop) { loop.RequestTermination(); }); - child_exited.set_value(); - }); + launch_info.SetMonitorProcessCallback([&main_loop](lldb::pid_t, int, int) { + main_loop.AddPendingCallback( + [](MainLoopBase &loop) { loop.RequestTermination(); }); + }); // Copy the current environment. launch_info.GetEnvironment() = Host::GetEnvironment(); @@ -550,27 +547,24 @@ int main_platform(int argc, char *argv[]) { return socket_error; } - std::promise<void> child_exited; MainLoop main_loop; { llvm::Expected<std::vector<MainLoopBase::ReadHandleUP>> platform_handles = platform_sock->Accept( main_loop, [progname, gdbserver_port, &inferior_arguments, log_file, - log_channels, &main_loop, &child_exited, + log_channels, &main_loop, &platform_handles](std::unique_ptr<Socket> sock_up) { printf("Connection established.\n"); - Status error = spawn_process( - progname, sock_up.get(), gdbserver_port, inferior_arguments, - log_file, log_channels, main_loop, child_exited); + Status error = spawn_process(progname, sock_up.get(), + gdbserver_port, inferior_arguments, + log_file, log_channels, main_loop); if (error.Fail()) { Log *log = GetLog(LLDBLog::Platform); LLDB_LOGF(log, "spawn_process failed: %s", error.AsCString()); WithColor::error() << "spawn_process failed: " << error.AsCString() << "\n"; - if (!g_server) { + if (!g_server) main_loop.RequestTermination(); - child_exited.set_value(); - } } if (!g_server) platform_handles->clear(); @@ -592,7 +586,6 @@ int main_platform(int argc, char *argv[]) { main_loop.Run(); } - child_exited.get_future().get(); fprintf(stderr, "lldb-server exiting...\n"); diff --git a/lldb/unittests/Host/MainLoopTest.cpp b/lldb/unittests/Host/MainLoopTest.cpp index b8417c9f00aa86..4688d4fed475b6 100644 --- a/lldb/unittests/Host/MainLoopTest.cpp +++ b/lldb/unittests/Host/MainLoopTest.cpp @@ -194,9 +194,6 @@ TEST_F(MainLoopTest, PendingCallbackTrigger) { add_callback2.set_value(); }); Status error; - auto socket_handle = loop.RegisterReadObject( - socketpair[1], [](MainLoopBase &) {}, error); - ASSERT_TRUE(socket_handle); ASSERT_THAT_ERROR(error.ToError(), llvm::Succeeded()); bool callback2_called = false; std::thread callback2_adder([&]() { @@ -212,15 +209,18 @@ TEST_F(MainLoopTest, PendingCallbackTrigger) { ASSERT_TRUE(callback2_called); } -// Regression test for assertion failure if a lot of callbacks end up -// being queued after loop exits. -TEST_F(MainLoopTest, PendingCallbackAfterLoopExited) { +TEST_F(MainLoopTest, ManyPendingCallbacks) { MainLoop loop; Status error; - ASSERT_TRUE(loop.Run().Success()); - // Try to fill the pipe buffer in. + // Try to fill up the pipe buffer and make sure bad things don't happen. This + // is a regression test for the case where writing to the interrupt pipe + // caused a deadlock when the pipe filled up (either because the main loop was + // not running, because it was slow, or because it was busy/blocked doing + // something else). for (int i = 0; i < 65536; ++i) - loop.AddPendingCallback([&](MainLoopBase &loop) {}); + loop.AddPendingCallback( + [&](MainLoopBase &loop) { loop.RequestTermination(); }); + ASSERT_TRUE(loop.Run().Success()); } #ifdef LLVM_ON_UNIX _______________________________________________ lldb-commits mailing list lldb-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/lldb-commits
