mgorny created this revision. mgorny added reviewers: labath, krytarowski, emaste, jingham. Herald added a project: All. mgorny requested review of this revision.
If lots of pending callbacks are added while the main loop has exited already, the trigger pipe buffer fills in, causing the write to fail and the related assertion to fail. To avoid this, add a boolean member indicating whether the callbacks have been triggered already. If the trigger was done, avoid writing to the pipe until loops proceeds to run them and resets the variable. Besides fixing the issue, this also avoids writing to the pipe multiple times if callbacks are added faster than the loop is able to process them. Previously, this would lead to the loop performing multiple read iterations from pipe unnecessarily. https://reviews.llvm.org/D135516 Files: lldb/include/lldb/Host/posix/MainLoopPosix.h lldb/source/Host/posix/MainLoopPosix.cpp lldb/unittests/Host/MainLoopTest.cpp Index: lldb/unittests/Host/MainLoopTest.cpp =================================================================== --- lldb/unittests/Host/MainLoopTest.cpp +++ lldb/unittests/Host/MainLoopTest.cpp @@ -171,6 +171,17 @@ 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) { + MainLoop loop; + Status error; + ASSERT_TRUE(loop.Run().Success()); + // Try to fill the pipe buffer in. + for (int i = 0; i < 65536; ++i) + loop.AddPendingCallback([&](MainLoopBase &loop) {}); +} + #ifdef LLVM_ON_UNIX TEST_F(MainLoopTest, DetectsEOF) { Index: lldb/source/Host/posix/MainLoopPosix.cpp =================================================================== --- lldb/source/Host/posix/MainLoopPosix.cpp +++ lldb/source/Host/posix/MainLoopPosix.cpp @@ -222,7 +222,7 @@ } #endif -MainLoopPosix::MainLoopPosix() { +MainLoopPosix::MainLoopPosix() : m_trigger_done(false) { Status error = m_trigger_pipe.CreateNew(/*child_process_inherit=*/false); assert(error.Success()); const int trigger_pipe_fd = m_trigger_pipe.GetReadFileDescriptor(); @@ -371,6 +371,7 @@ impl.ProcessEvents(); + m_trigger_done = false; ProcessPendingCallbacks(); } return Status(); @@ -395,10 +396,14 @@ } void MainLoopPosix::TriggerPendingCallbacks() { + if (m_trigger_done) + return; + char c = '.'; size_t bytes_written; Status error = m_trigger_pipe.Write(&c, 1, bytes_written); assert(error.Success()); UNUSED_IF_ASSERT_DISABLED(error); assert(bytes_written == 1); + m_trigger_done = true; } Index: lldb/include/lldb/Host/posix/MainLoopPosix.h =================================================================== --- lldb/include/lldb/Host/posix/MainLoopPosix.h +++ lldb/include/lldb/Host/posix/MainLoopPosix.h @@ -13,6 +13,7 @@ #include "lldb/Host/MainLoopBase.h" #include "lldb/Host/Pipe.h" #include "llvm/ADT/DenseMap.h" +#include <atomic> #include <csignal> #include <list> #include <vector> @@ -87,6 +88,7 @@ llvm::DenseMap<IOObject::WaitableHandle, Callback> m_read_fds; llvm::DenseMap<int, SignalInfo> m_signals; Pipe m_trigger_pipe; + std::atomic<bool> m_trigger_done; #if HAVE_SYS_EVENT_H int m_kqueue; #endif
Index: lldb/unittests/Host/MainLoopTest.cpp =================================================================== --- lldb/unittests/Host/MainLoopTest.cpp +++ lldb/unittests/Host/MainLoopTest.cpp @@ -171,6 +171,17 @@ 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) { + MainLoop loop; + Status error; + ASSERT_TRUE(loop.Run().Success()); + // Try to fill the pipe buffer in. + for (int i = 0; i < 65536; ++i) + loop.AddPendingCallback([&](MainLoopBase &loop) {}); +} + #ifdef LLVM_ON_UNIX TEST_F(MainLoopTest, DetectsEOF) { Index: lldb/source/Host/posix/MainLoopPosix.cpp =================================================================== --- lldb/source/Host/posix/MainLoopPosix.cpp +++ lldb/source/Host/posix/MainLoopPosix.cpp @@ -222,7 +222,7 @@ } #endif -MainLoopPosix::MainLoopPosix() { +MainLoopPosix::MainLoopPosix() : m_trigger_done(false) { Status error = m_trigger_pipe.CreateNew(/*child_process_inherit=*/false); assert(error.Success()); const int trigger_pipe_fd = m_trigger_pipe.GetReadFileDescriptor(); @@ -371,6 +371,7 @@ impl.ProcessEvents(); + m_trigger_done = false; ProcessPendingCallbacks(); } return Status(); @@ -395,10 +396,14 @@ } void MainLoopPosix::TriggerPendingCallbacks() { + if (m_trigger_done) + return; + char c = '.'; size_t bytes_written; Status error = m_trigger_pipe.Write(&c, 1, bytes_written); assert(error.Success()); UNUSED_IF_ASSERT_DISABLED(error); assert(bytes_written == 1); + m_trigger_done = true; } Index: lldb/include/lldb/Host/posix/MainLoopPosix.h =================================================================== --- lldb/include/lldb/Host/posix/MainLoopPosix.h +++ lldb/include/lldb/Host/posix/MainLoopPosix.h @@ -13,6 +13,7 @@ #include "lldb/Host/MainLoopBase.h" #include "lldb/Host/Pipe.h" #include "llvm/ADT/DenseMap.h" +#include <atomic> #include <csignal> #include <list> #include <vector> @@ -87,6 +88,7 @@ llvm::DenseMap<IOObject::WaitableHandle, Callback> m_read_fds; llvm::DenseMap<int, SignalInfo> m_signals; Pipe m_trigger_pipe; + std::atomic<bool> m_trigger_done; #if HAVE_SYS_EVENT_H int m_kqueue; #endif
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