Files
llvm/lldb/tools/lldb-dap/LLDBUtils.cpp
jeffreytan81 f838fa820f New ThreadPlanSingleThreadTimeout to resolve potential deadlock in single thread stepping (#90930)
This PR introduces a new `ThreadPlanSingleThreadTimeout` that will be
used to address potential deadlock during single-thread stepping.

While debugging a target with a non-trivial number of threads (around
5000 threads in one example target), we noticed that a simple step over
can take as long as 10 seconds. Enabling single-thread stepping mode
significantly reduces the stepping time to around 3 seconds. However,
this can introduce deadlock if we try to step over a method that depends
on other threads to release a lock.

To address this issue, we introduce a new
`ThreadPlanSingleThreadTimeout` that can be controlled by the
`target.process.thread.single-thread-plan-timeout` setting during
single-thread stepping mode. The concept involves counting the elapsed
time since the last internal stop to detect overall stepping progress.
Once a timeout occurs, we assume the target is not making progress due
to a potential deadlock, as mentioned above. We then send a new async
interrupt, resume all threads, and `ThreadPlanSingleThreadTimeout`
completes its task.

To support this design, the major changes made in this PR are:
1. `ThreadPlanSingleThreadTimeout` is popped during every internal stop
and reset (re-pushed) to the top of the stack (as a leaf node) during
resume. This is achieved by always returning `true` from
`ThreadPlanSingleThreadTimeout::DoPlanExplainsStop()` and
`ThreadPlanSingleThreadTimeout::MischiefManaged()`.
2. A new thread-specific async interrupt stop is introduced, which can
be detected/consumed by `ThreadPlanSingleThreadTimeout`.
3. The clearing of branch breakpoints in the range thread plan has been
moved from `DoPlanExplainsStop()` to `ShouldStop()`, as it is not
guaranteed that it will be called.

The detailed design is discussed in the RFC below:

[https://discourse.llvm.org/t/improve-single-thread-stepping/74599](https://discourse.llvm.org/t/improve-single-thread-stepping/74599)

---------

Co-authored-by: jeffreytan81 <jeffreytan@fb.com>
2024-08-05 17:26:39 -07:00

139 lines
4.3 KiB
C++

//===-- LLDBUtils.cpp -------------------------------------------*- C++ -*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
#include "LLDBUtils.h"
#include "DAP.h"
#include <mutex>
namespace lldb_dap {
bool RunLLDBCommands(llvm::StringRef prefix,
const llvm::ArrayRef<std::string> &commands,
llvm::raw_ostream &strm, bool parse_command_directives) {
if (commands.empty())
return true;
bool did_print_prefix = false;
lldb::SBCommandInterpreter interp = g_dap.debugger.GetCommandInterpreter();
for (llvm::StringRef command : commands) {
lldb::SBCommandReturnObject result;
bool quiet_on_success = false;
bool check_error = false;
while (parse_command_directives) {
if (command.starts_with("?")) {
command = command.drop_front();
quiet_on_success = true;
} else if (command.starts_with("!")) {
command = command.drop_front();
check_error = true;
} else {
break;
}
}
{
// Prevent simultaneous calls to HandleCommand, e.g. EventThreadFunction
// may asynchronously call RunExitCommands when we are already calling
// RunTerminateCommands.
static std::mutex handle_command_mutex;
std::lock_guard<std::mutex> locker(handle_command_mutex);
interp.HandleCommand(command.str().c_str(), result);
}
const bool got_error = !result.Succeeded();
// The if statement below is assuming we always print out `!` prefixed
// lines. The only time we don't print is when we have `quiet_on_success ==
// true` and we don't have an error.
if (quiet_on_success ? got_error : true) {
if (!did_print_prefix && !prefix.empty()) {
strm << prefix << "\n";
did_print_prefix = true;
}
strm << "(lldb) " << command << "\n";
auto output_len = result.GetOutputSize();
if (output_len) {
const char *output = result.GetOutput();
strm << output;
}
auto error_len = result.GetErrorSize();
if (error_len) {
const char *error = result.GetError();
strm << error;
}
}
if (check_error && got_error)
return false; // Stop running commands.
}
return true;
}
std::string RunLLDBCommands(llvm::StringRef prefix,
const llvm::ArrayRef<std::string> &commands,
bool &required_command_failed,
bool parse_command_directives) {
required_command_failed = false;
std::string s;
llvm::raw_string_ostream strm(s);
required_command_failed =
!RunLLDBCommands(prefix, commands, strm, parse_command_directives);
strm.flush();
return s;
}
std::string
RunLLDBCommandsVerbatim(llvm::StringRef prefix,
const llvm::ArrayRef<std::string> &commands) {
bool required_command_failed = false;
return RunLLDBCommands(prefix, commands, required_command_failed,
/*parse_command_directives=*/false);
}
bool ThreadHasStopReason(lldb::SBThread &thread) {
switch (thread.GetStopReason()) {
case lldb::eStopReasonTrace:
case lldb::eStopReasonPlanComplete:
case lldb::eStopReasonBreakpoint:
case lldb::eStopReasonWatchpoint:
case lldb::eStopReasonInstrumentation:
case lldb::eStopReasonSignal:
case lldb::eStopReasonException:
case lldb::eStopReasonExec:
case lldb::eStopReasonProcessorTrace:
case lldb::eStopReasonFork:
case lldb::eStopReasonVFork:
case lldb::eStopReasonVForkDone:
case lldb::eStopReasonInterrupt:
return true;
case lldb::eStopReasonThreadExiting:
case lldb::eStopReasonInvalid:
case lldb::eStopReasonNone:
break;
}
return false;
}
static uint32_t constexpr THREAD_INDEX_SHIFT = 19;
uint32_t GetLLDBThreadIndexID(uint64_t dap_frame_id) {
return dap_frame_id >> THREAD_INDEX_SHIFT;
}
uint32_t GetLLDBFrameID(uint64_t dap_frame_id) {
return dap_frame_id & ((1u << THREAD_INDEX_SHIFT) - 1);
}
int64_t MakeDAPFrameID(lldb::SBFrame &frame) {
return ((int64_t)frame.GetThread().GetIndexID() << THREAD_INDEX_SHIFT) |
frame.GetFrameID();
}
} // namespace lldb_dap