llvm-project/lldb/source/Host/posix/MainLoopPosix.cpp

//===-- MainLoopPosix.cpp ---------------------------------------*- C++ -*-===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//

#include "lldb/Host/posix/MainLoopPosix.h"

#include <vector>

#include "lldb/Core/Error.h"

using namespace lldb;
using namespace lldb_private;

static sig_atomic_t g_signal_flags[NSIG];

static void
SignalHandler(int signo, siginfo_t *info, void *)
{
    assert(signo < NSIG);
    g_signal_flags[signo] = 1;
}


MainLoopPosix::~MainLoopPosix()
{
    assert(m_read_fds.size() == 0);
    assert(m_signals.size() == 0);
}

MainLoopPosix::ReadHandleUP
MainLoopPosix::RegisterReadObject(const IOObjectSP &object_sp, const Callback &callback, Error &error)
{
    if (!object_sp || !object_sp->IsValid())
    {
        error.SetErrorString("IO object is not valid.");
        return nullptr;
    }

    const bool inserted = m_read_fds.insert({object_sp->GetWaitableHandle(), callback}).second;
    if (! inserted)
    {
        error.SetErrorStringWithFormat("File descriptor %d already monitored.",
                object_sp->GetWaitableHandle());
        return nullptr;
    }

    return CreateReadHandle(object_sp);
}

// We shall block the signal, then install the signal handler. The signal will be unblocked in
// the Run() function to check for signal delivery.
MainLoopPosix::SignalHandleUP
MainLoopPosix::RegisterSignal(int signo, const Callback &callback, Error &error)
{
    if (m_signals.find(signo) != m_signals.end())
    {
        error.SetErrorStringWithFormat("Signal %d already monitored.", signo);
        return nullptr;
    }

    SignalInfo info;
    info.callback = callback;
    struct sigaction new_action;
    new_action.sa_sigaction = &SignalHandler;
    new_action.sa_flags = SA_SIGINFO;
    sigemptyset(&new_action.sa_mask);
    sigaddset(&new_action.sa_mask, signo);

    sigset_t old_set;
    if (int ret = pthread_sigmask(SIG_BLOCK, &new_action.sa_mask, &old_set))
    {
        error.SetErrorStringWithFormat("pthread_sigmask failed with error %d\n", ret);
        return nullptr;
    }

    info.was_blocked = sigismember(&old_set, signo);
    if (sigaction(signo, &new_action, &info.old_action) == -1)
    {
        error.SetErrorToErrno();
        if (!info.was_blocked)
            pthread_sigmask(SIG_UNBLOCK, &new_action.sa_mask, nullptr);
        return nullptr;
    }

    m_signals.insert({signo, info});
    g_signal_flags[signo] = 0;

    return SignalHandleUP(new SignalHandle(*this, signo));
}

void
MainLoopPosix::UnregisterReadObject(IOObject::WaitableHandle handle)
{
    bool erased = m_read_fds.erase(handle);
    (void) erased;
    assert(erased);
}

void
MainLoopPosix::UnregisterSignal(int signo)
{
    // We undo the actions of RegisterSignal on a best-effort basis.
    auto it = m_signals.find(signo);
    assert(it != m_signals.end());

    sigaction(signo, &it->second.old_action, nullptr);

    sigset_t set;
    sigemptyset(&set);
    sigaddset(&set, signo);
    pthread_sigmask(it->second.was_blocked ? SIG_BLOCK : SIG_UNBLOCK, &set, nullptr);

    m_signals.erase(it);
}

Error
MainLoopPosix::Run()
{
    std::vector<int> signals;
    sigset_t sigmask;
    std::vector<int> read_fds;
    fd_set read_fd_set;
    m_terminate_request = false;

    // run until termination or until we run out of things to listen to
    while (! m_terminate_request && (!m_read_fds.empty() || !m_signals.empty()))
    {
        // To avoid problems with callbacks changing the things we're supposed to listen to, we
        // will store the *real* list of events separately.
        signals.clear();
        read_fds.clear();
        FD_ZERO(&read_fd_set);
        int nfds = 0;

        if (int ret = pthread_sigmask(SIG_SETMASK, nullptr, &sigmask))
            return Error("pthread_sigmask failed with error %d\n", ret);

        for (const auto &fd: m_read_fds)
        {
            read_fds.push_back(fd.first);
            FD_SET(fd.first, &read_fd_set);
            nfds = std::max(nfds, fd.first+1);
        }

        for (const auto &sig: m_signals)
        {
            signals.push_back(sig.first);
            sigdelset(&sigmask, sig.first);
        }

        if (pselect(nfds, &read_fd_set, nullptr, nullptr, nullptr, &sigmask) == -1 && errno != EINTR)
            return Error(errno, eErrorTypePOSIX);

        for (int sig: signals)
        {
            if (g_signal_flags[sig] == 0)
                continue; // No signal
            g_signal_flags[sig] = 0;

            auto it = m_signals.find(sig);
            if (it == m_signals.end())
                continue; // Signal must have gotten unregistered in the meantime

            it->second.callback(*this); // Do the work

            if (m_terminate_request)
                return Error();
        }

        for (int fd: read_fds)
        {
            if (!FD_ISSET(fd, &read_fd_set))
                continue; // Not ready

            auto it = m_read_fds.find(fd);
            if (it == m_read_fds.end())
                continue; // File descriptor must have gotten unregistered in the meantime

            it->second(*this); // Do the work

            if (m_terminate_request)
                return Error();
        }
    }
    return Error();
}