[Lldb-commits] [lldb] [lldb] Add an Alarm class for coalescing progress reports (PR #85329)

[Adrian Prantl via lldb-commits]

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@@ -0,0 +1,193 @@
+//===-- Alarm.cpp ---------------------------------------------------------===//
+//
+// 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 "lldb/Host/Alarm.h"
+#include "lldb/Host/ThreadLauncher.h"
+#include "lldb/Utility/LLDBLog.h"
+#include "lldb/Utility/Log.h"
+
+using namespace lldb;
+using namespace lldb_private;
+
+Alarm::Alarm(Duration timeout, bool run_callback_on_exit)
+    : m_timeout(timeout), m_run_callbacks_on_exit(run_callback_on_exit) {
+  StartAlarmThread();
+}
+
+Alarm::~Alarm() { StopAlarmThread(); }
+
+Alarm::Handle Alarm::Create(std::function<void()> callback) {
+  // Gracefully deal with the unlikely event that the alarm thread failed to
+  // launch.
+  if (!AlarmThreadRunning())
+    return INVALID_HANDLE;
+
+  // Compute the next expiration before we take the lock. This ensures that
+  // waiting on the lock doesn't eat into the timeout.
+  const TimePoint expiration = GetNextExpiration();
+
+  Handle handle = INVALID_HANDLE;
+
+  {
+    std::lock_guard alarm_guard(m_alarm_mutex);
+
+    // Create a new unique entry and remember its handle.
+    m_entries.emplace_back(callback, expiration);
+    handle = m_entries.back().handle;
+
+    // Tell the alarm thread we need to recompute the next alarm.
+    m_recompute_next_alarm = true;
+  }
+
+  m_alarm_cv.notify_one();
+  return handle;
+}
+
+bool Alarm::Restart(Handle handle) {
+  // Gracefully deal with the unlikely event that the alarm thread failed to
+  // launch.
+  if (!AlarmThreadRunning())
+    return false;
+
+  // Compute the next expiration before we take the lock. This ensures that
+  // waiting on the lock doesn't eat into the timeout.
+  const TimePoint expiration = GetNextExpiration();
+
+  {
+    std::lock_guard alarm_guard(m_alarm_mutex);
+
+    // Find the entry corresponding to the given handle.
+    const auto it =
+        std::find_if(m_entries.begin(), m_entries.end(),
+                     [handle](Entry &entry) { return entry.handle == handle; });
+    if (it == m_entries.end())
+      return false;
+
+    // Update the expiration.
+    it->expiration = expiration;
+
+    // Tell the alarm thread we need to recompute the next alarm.
+    m_recompute_next_alarm = true;
+  }
+
+  m_alarm_cv.notify_one();
+  return true;
+}
+
+bool Alarm::Cancel(Handle handle) {
+  // Gracefully deal with the unlikely event that the alarm thread failed to
+  // launch.
+  if (!AlarmThreadRunning())
+    return false;
+
+  {
+    std::lock_guard alarm_guard(m_alarm_mutex);
+
+    const auto it =
+        std::find_if(m_entries.begin(), m_entries.end(),
+                     [handle](Entry &entry) { return entry.handle == handle; });
+
+    if (it == m_entries.end())
+      return false;
+
+    m_entries.erase(it);
+  }
+
+  // No need to notify the alarm thread. This only affects the alarm thread if
+  // we removed the entry that corresponds to the next alarm. If that's the
+  // case, the thread will wake up as scheduled, find no expired events, and
+  // recompute the next alarm time.
+  return true;
+}
+
+Alarm::Entry::Entry(Alarm::Callback callback, Alarm::TimePoint expiration)
+    : handle(Alarm::GetNextUniqueHandle()), callback(std::move(callback)),
+      expiration(std::move(expiration)) {}
+
+void Alarm::StartAlarmThread() {
+  if (!m_alarm_thread.IsJoinable()) {
+    llvm::Expected<HostThread> alarm_thread = ThreadLauncher::LaunchThread(
+        "lldb.debugger.alarm-thread", [this] { return AlarmThread(); },
+        8 * 1024 * 1024); // Use larger 8MB stack for this thread
+    if (alarm_thread) {
+      m_alarm_thread = *alarm_thread;
+    } else {
+      LLDB_LOG_ERROR(GetLog(LLDBLog::Host), alarm_thread.takeError(),
+                     "failed to launch host thread: {0}");
+    }
+  }
+}
+
+void Alarm::StopAlarmThread() {
+  if (m_alarm_thread.IsJoinable()) {
+    {
+      std::lock_guard alarm_guard(m_alarm_mutex);
+      m_exit = true;
+    }
+    m_alarm_cv.notify_one();
+    m_alarm_thread.Join(nullptr);
+  }
+}
+
+bool Alarm::AlarmThreadRunning() { return m_alarm_thread.IsJoinable(); }
+
+lldb::thread_result_t Alarm::AlarmThread() {
----------------
adrian-prantl wrote:

I feel like this function could use some high-level comments above each code block

https://github.com/llvm/llvm-project/pull/85329