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JDevlieghereJDevlieghere
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[lldb-dap] Implement a MemoryMonitor (#129332)
This implements a memory monitor for macOS, Linux and Windows. It registers a callback that invokes `SBDebugger::MemoryPressureDetected` when a low memory event is detected. This is motivated by the new server mode, where the lldb-dap process will live across multiple debug sessions and will use more memory due to caching.
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‎lldb/include/lldb/Host/MemoryMonitor.h‎

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//===-- MemoryMonitor.h ---------------------------------------------------===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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#ifndef LLDB_HOST_MEMORYMONITOR_H
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#define LLDB_HOST_MEMORYMONITOR_H
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#include <functional>
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#include <memory>
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namespace lldb_private {
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class MemoryMonitor {
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public:
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using Callback = std::function<void()>;
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MemoryMonitor(Callback callback) : m_callback(callback) {}
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virtual ~MemoryMonitor() = default;
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/// MemoryMonitor is not copyable.
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/// @{
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MemoryMonitor(const MemoryMonitor &) = delete;
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MemoryMonitor &operator=(const MemoryMonitor &) = delete;
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/// @}
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static std::unique_ptr<MemoryMonitor> Create(Callback callback);
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virtual void Start() = 0;
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virtual void Stop() = 0;
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protected:
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Callback m_callback;
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};
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} // namespace lldb_private
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#endif

‎lldb/source/Host/CMakeLists.txt‎

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@@ -27,6 +27,7 @@ add_host_subdirectory(common
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common/LockFileBase.cpp
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common/LZMA.cpp
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common/MainLoopBase.cpp
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common/MemoryMonitor.cpp
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common/MonitoringProcessLauncher.cpp
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common/NativeProcessProtocol.cpp
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common/NativeRegisterContext.cpp
@@ -136,7 +137,7 @@ else()
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elseif (CMAKE_SYSTEM_NAME MATCHES "AIX")
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add_host_subdirectory(aix
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aix/HostInfoAIX.cpp
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)
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)
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endif()
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endif()
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‎lldb/source/Host/common/MemoryMonitor.cpp‎

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//===-- MemoryMonitor.cpp -------------------------------------------------===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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#include "lldb/Host/MemoryMonitor.h"
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#include "lldb/Host/HostThread.h"
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#include "lldb/Host/ThreadLauncher.h"
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#include "lldb/Utility/LLDBLog.h"
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#include "lldb/Utility/Log.h"
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#include "llvm/ADT/ScopeExit.h"
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#include "llvm/Support/Error.h"
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#include <atomic>
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#include <cstddef>
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#include <cstdio>
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#include <cstring>
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#if defined(__linux__)
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#include <fcntl.h>
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#include <poll.h>
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#include <unistd.h>
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#endif
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#if defined(_WIN32)
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#include <windows.h>
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#endif
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using namespace lldb_private;
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class MemoryMonitorPoll : public MemoryMonitor {
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public:
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using MemoryMonitor::MemoryMonitor;
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lldb::thread_result_t MonitorThread() {
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#if defined(__linux__)
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struct pollfd fds;
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fds.fd = open("/proc/pressure/memory", O_RDWR | O_NONBLOCK);
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if (fds.fd < 0)
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return {};
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fds.events = POLLPRI;
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auto cleanup = llvm::make_scope_exit([&]() { close(fds.fd); });
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// Detect a 50ms stall in a 2 second time window.
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const char trig[] = "some 50000 2000000";
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if (write(fds.fd, trig, strlen(trig) + 1) < 0)
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return {};
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while (!m_done) {
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int n = poll(&fds, 1, g_timeout);
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if (n > 0) {
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if (fds.revents & POLLERR)
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return {};
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if (fds.revents & POLLPRI)
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m_callback();
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}
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}
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#endif
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#if defined(_WIN32)
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HANDLE low_memory_notification =
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CreateMemoryResourceNotification(LowMemoryResourceNotification);
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if (!low_memory_notification)
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return {};
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while (!m_done) {
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if (WaitForSingleObject(low_memory_notification, g_timeout) ==
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WAIT_OBJECT_0) {
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m_callback();
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}
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}
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#endif
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return {};
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}
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void Start() override {
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llvm::Expected<HostThread> memory_monitor_thread =
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ThreadLauncher::LaunchThread("lldb.debugger.memory-monitor",
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[this] { return MonitorThread(); });
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if (memory_monitor_thread) {
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m_memory_monitor_thread = *memory_monitor_thread;
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} else {
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LLDB_LOG_ERROR(GetLog(LLDBLog::Host), memory_monitor_thread.takeError(),
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"failed to launch host thread: {0}");
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}
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}
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void Stop() override {
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if (m_memory_monitor_thread.IsJoinable()) {
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m_done = true;
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m_memory_monitor_thread.Join(nullptr);
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}
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}
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private:
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static constexpr uint32_t g_timeout = 1000;
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std::atomic<bool> m_done = false;
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HostThread m_memory_monitor_thread;
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};
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#if !defined(__APPLE__)
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std::unique_ptr<MemoryMonitor> MemoryMonitor::Create(Callback callback) {
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return std::make_unique<MemoryMonitorPoll>(callback);
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}
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#endif

‎lldb/source/Host/macosx/objcxx/CMakeLists.txt‎

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@@ -6,6 +6,7 @@ add_lldb_library(lldbHostMacOSXObjCXX NO_PLUGIN_DEPENDENCIES
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Host.mm
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HostInfoMacOSX.mm
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HostThreadMacOSX.mm
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MemoryMonitorMacOSX.mm
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LINK_LIBS
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lldbUtility

‎lldb/source/Host/macosx/objcxx/MemoryMonitorMacOSX.mm‎

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//===-- MemoryMonitorMacOSX.mm --------------------------------------------===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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#include "lldb/Host/MemoryMonitor.h"
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#include <cassert>
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#include <dispatch/dispatch.h>
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using namespace lldb_private;
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class MemoryMonitorMacOSX : public MemoryMonitor {
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using MemoryMonitor::MemoryMonitor;
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void Start() override {
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m_memory_pressure_source = dispatch_source_create(
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DISPATCH_SOURCE_TYPE_MEMORYPRESSURE, 0,
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DISPATCH_MEMORYPRESSURE_WARN | DISPATCH_MEMORYPRESSURE_CRITICAL,
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dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0));
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if (!m_memory_pressure_source)
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return;
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dispatch_source_set_event_handler(m_memory_pressure_source, ^{
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dispatch_source_memorypressure_flags_t pressureLevel =
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dispatch_source_get_data(m_memory_pressure_source);
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if (pressureLevel &
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(DISPATCH_MEMORYPRESSURE_WARN | DISPATCH_MEMORYPRESSURE_CRITICAL)) {
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m_callback();
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}
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});
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dispatch_activate(m_memory_pressure_source);
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printf("Started\n");
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}
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void Stop() override {
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if (m_memory_pressure_source) {
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dispatch_source_cancel(m_memory_pressure_source);
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dispatch_release(m_memory_pressure_source);
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}
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}
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private:
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dispatch_source_t m_memory_pressure_source;
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};
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std::unique_ptr<MemoryMonitor> MemoryMonitor::Create(Callback callback) {
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return std::make_unique<MemoryMonitorMacOSX>(callback);
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}

‎lldb/tools/lldb-dap/lldb-dap.cpp‎

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#include "EventHelper.h"
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#include "Handler/RequestHandler.h"
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#include "RunInTerminal.h"
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#include "lldb/API/SBDebugger.h"
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#include "lldb/API/SBStream.h"
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#include "lldb/Host/Config.h"
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#include "lldb/Host/File.h"
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#include "lldb/Host/MainLoop.h"
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#include "lldb/Host/MainLoopBase.h"
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#include "lldb/Host/MemoryMonitor.h"
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#include "lldb/Host/Socket.h"
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#include "lldb/Utility/Status.h"
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#include "lldb/Utility/UriParser.h"
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return EXIT_FAILURE;
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}
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// Create a memory monitor. This can return nullptr if the host platform is
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// not supported.
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std::unique_ptr<lldb_private::MemoryMonitor> memory_monitor =
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lldb_private::MemoryMonitor::Create([&]() {
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if (log)
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*log << "memory pressure detected\n";
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lldb::SBDebugger::MemoryPressureDetected();
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});
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if (memory_monitor)
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memory_monitor->Start();
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// Terminate the debugger before the C++ destructor chain kicks in.
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auto terminate_debugger =
509-
llvm::make_scope_exit([] { lldb::SBDebugger::Terminate(); });
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auto terminate_debugger = llvm::make_scope_exit([&] {
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if (memory_monitor)
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memory_monitor->Stop();
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lldb::SBDebugger::Terminate();
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});
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std::vector<std::string> pre_init_commands;
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for (const std::string &arg :

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