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/*
* Copyright (C) 2018 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#include <sys/types.h>
#include <sys/wait.h>
#include <assert.h>
#include <errno.h>
#include <signal.h>
#include <stdio.h>
#include <map>
#include <glog/logging.h>
#include "common/libs/fs/shared_select.h"
#include "host/commands/launch/process_monitor.h"
namespace cvd {
namespace {
void NotifyThread(SharedFD fd) {
// The restarter thread is (likely) blocked on a call to select, to make it
// wake up and do some work we write something (anything, the content is not
// important) into the main side of the socket pair so that the call to select
// returns and the notification fd (restarter side of the socket pair) is
// marked as ready to read.
char buffer = 'a';
fd->Write(&buffer, sizeof(buffer));
}
void ConsumeNotifications(SharedFD fd) {
// Once the starter thread is waken up due to a notification, the calls to
// select will continue to return immediately unless we read what was written
// on the main side of the socket pair. More than one notification can
// accumulate before the restarter thread consumes them, so we attempt to read
// more than it's written to consume them all at once. In the unlikely case of
// more than 8 notifications acummulating we simply read the first 8 and have
// another iteration on the restarter thread loop.
char buffer[8];
fd->Read(buffer, sizeof(buffer));
}
} // namespace
ProcessMonitor::ProcessMonitor() {
if (!SharedFD::SocketPair(AF_LOCAL, SOCK_STREAM, 0, &thread_comm_main_,
&thread_comm_monitor_)) {
LOG(ERROR) << "Unable to create restarter communication socket pair: "
<< strerror(errno);
return;
}
monitor_thread_ = std::thread([this]() { MonitorRoutine(); });
}
void ProcessMonitor::StartSubprocess(Command cmd, OnSocketReadyCb callback) {
auto proc = cmd.StartInGroup(true);
if (!proc.Started()) {
LOG(ERROR) << "Failed to start process";
return;
}
MonitorExistingSubprocess(std::move(cmd), std::move(proc), callback);
}
void ProcessMonitor::MonitorExistingSubprocess(Command cmd, Subprocess proc,
OnSocketReadyCb callback) {
{
std::lock_guard<std::mutex> lock(processes_mutex_);
monitored_processes_.push_back(MonitorEntry());
auto& entry = monitored_processes_.back();
entry.cmd.reset(new Command(std::move(cmd)));
entry.proc.reset(new Subprocess(std::move(proc)));
entry.on_control_socket_ready_cb = callback;
}
// Wake the restarter thread up so that it starts monitoring this subprocess
// Do this after releasing the lock so that the restarter thread is free to
// begin work as soon as select returns.
NotifyThread(thread_comm_main_);
}
bool ProcessMonitor::StopMonitoredProcesses() {
// Because the mutex is held while this function executes, the restarter
// thread is kept blocked and by the time it resumes execution there are no
// more processes to monitor
std::lock_guard<std::mutex> lock(processes_mutex_);
bool result = true;
// Processes were started in the order they appear in the vector, stop them in
// reverse order for symmetry.
for (auto entry_it = monitored_processes_.rbegin();
entry_it != monitored_processes_.rend(); ++entry_it) {
auto& entry = *entry_it;
result = result && entry.proc->Stop();
}
// Wait for all processes to actually exit.
for (auto& entry : monitored_processes_) {
// Most processes are being killed by signals, calling Wait(void) would be
// too verbose on the logs.
int wstatus;
auto ret = entry.proc->Wait(&wstatus, 0);
if (ret < 0) {
LOG(WARNING) << "Failed to wait for process "
<< entry.cmd->GetShortName();
}
}
// Clear the list to ensure they are not started again
monitored_processes_.clear();
return result;
}
bool ProcessMonitor::RestartOnExitCb(MonitorEntry* entry) {
// Make sure the process actually exited
char buffer[16];
auto bytes_read = entry->proc->control_socket()->Read(buffer, sizeof(buffer));
if (bytes_read > 0) {
LOG(WARNING) << "Subprocess " << entry->cmd->GetShortName() << " wrote "
<< bytes_read
<< " bytes on the control socket, this is unexpected";
// The process may not have exited, continue monitoring without restarting
return true;
}
LOG(INFO) << "Detected exit of monitored subprocess";
// Make sure the subprocess isn't left in a zombie state, and that the
// pid is logged
int wstatus;
auto wait_ret = TEMP_FAILURE_RETRY(entry->proc->Wait(&wstatus, 0));
// None of the error conditions specified on waitpid(2) apply
assert(wait_ret > 0);
if (WIFEXITED(wstatus)) {
LOG(INFO) << "Subprocess " << entry->cmd->GetShortName() << " (" << wait_ret
<< ") has exited with exit code " << WEXITSTATUS(wstatus);
} else if (WIFSIGNALED(wstatus)) {
LOG(ERROR) << "Subprocess " << entry->cmd->GetShortName() << " ("
<< wait_ret
<< ") was interrupted by a signal: " << WTERMSIG(wstatus);
} else {
LOG(INFO) << "subprocess " << entry->cmd->GetShortName() << " (" << wait_ret
<< ") has exited for unknown reasons";
}
entry->proc.reset(new Subprocess(entry->cmd->Start(true)));
return true;
}
bool ProcessMonitor::DoNotMonitorCb(MonitorEntry*) { return false; }
void ProcessMonitor::MonitorRoutine() {
LOG(INFO) << "Started monitoring subprocesses";
do {
SharedFDSet read_set;
read_set.Set(thread_comm_monitor_);
{
std::lock_guard<std::mutex> lock(processes_mutex_);
for (auto& monitored_process : monitored_processes_) {
auto control_socket = monitored_process.proc->control_socket();
if (!control_socket->IsOpen()) {
LOG(ERROR) << "The control socket for "
<< monitored_process.cmd->GetShortName()
<< " is closed, it's effectively NOT being monitored";
}
read_set.Set(control_socket);
}
}
// We can't call select while holding the lock as it would lead to a
// deadlock (restarter thread waiting for notifications from main thread,
// main thread waiting for the lock)
int num_fds = cvd::Select(&read_set, nullptr, nullptr, nullptr);
if (num_fds < 0) {
LOG(ERROR) << "Select call returned error on restarter thread: "
<< strerror(errno);
}
if (num_fds > 0) {
// Try the communication fd, it's the most likely to be set
if (read_set.IsSet(thread_comm_monitor_)) {
--num_fds;
ConsumeNotifications(thread_comm_monitor_);
}
}
{
std::lock_guard<std::mutex> lock(processes_mutex_);
// Keep track of the number of file descriptors ready for read, chances
// are we don't need to go over the entire list of subprocesses
auto it = monitored_processes_.begin();
while (it != monitored_processes_.end()) {
auto control_socket = it->proc->control_socket();
bool keep_monitoring = true;
if (read_set.IsSet(control_socket)) {
--num_fds;
keep_monitoring = it->on_control_socket_ready_cb(&(*it));
}
if (keep_monitoring) {
++it;
} else {
it = monitored_processes_.erase(it);
}
}
}
assert(num_fds == 0);
} while (true);
}
} // namespace cvd
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