xref: /llvm-project-15.0.7/lldb/source/Utility/SelectHelper.cpp (revision fdb2d99e)

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

#if defined(__APPLE__)
// Enable this special support for Apple builds where we can have unlimited
// select bounds. We tried switching to poll() and kqueue and we were panicing
// the kernel, so we have to stick with select for now.
#define _DARWIN_UNLIMITED_SELECT
#endif

// C Includes
#include <errno.h>
#if defined(_WIN32)
// Define NOMINMAX to avoid macros that conflict with std::min and std::max
#define NOMINMAX
#include <winsock2.h>
#else
#include <sys/select.h>
#endif

// C++ Includes
#include <algorithm>

// Other libraries and framework includes
#include "llvm/ADT/SmallVector.h"

// Project includes
#include "lldb/Core/Error.h"
#include "lldb/Utility/SelectHelper.h"
#include "lldb/Utility/LLDBAssert.h"

SelectHelper::SelectHelper() :
    m_fd_map(),
    m_end_time() // Infinite timeout unless SelectHelper::SetTimeout() gets called
{
}

void
SelectHelper::SetTimeout(const std::chrono::microseconds &timeout)
{
    using namespace std::chrono;
    m_end_time = steady_clock::time_point(steady_clock::now() + timeout);
}

void
SelectHelper::FDSetRead(int fd)
{
    m_fd_map[fd].read_set = true;
}

void
SelectHelper::FDSetWrite(int fd)
{
    m_fd_map[fd].write_set = true;
}

void
SelectHelper::FDSetError(int fd)
{
    m_fd_map[fd].error_set = true;
}

bool
SelectHelper::FDIsSetRead(int fd) const
{
    auto pos = m_fd_map.find(fd);
    if (pos != m_fd_map.end())
        return pos->second.read_is_set;
    else
        return false;
}

bool
SelectHelper::FDIsSetWrite(int fd) const
{
    auto pos = m_fd_map.find(fd);
    if (pos != m_fd_map.end())
        return pos->second.write_is_set;
    else
        return false;
}

bool
SelectHelper::FDIsSetError(int fd) const
{
    auto pos = m_fd_map.find(fd);
    if (pos != m_fd_map.end())
        return pos->second.error_is_set;
    else
        return false;
}

lldb_private::Error
SelectHelper::Select()
{
    lldb_private::Error error;
#ifdef _MSC_VER
    // On windows FD_SETSIZE limits the number of file descriptors, not their numeric value.
    lldbassert(m_fd_map.size() <= FD_SETSIZE);
    if (m_fd_map.size() > FD_SETSIZE)
        return lldb_private::Error("Too many file descriptors for select()");
#endif

    int max_read_fd = -1;
    int max_write_fd = -1;
    int max_error_fd = -1;
    int max_fd = -1;
    for (auto &pair : m_fd_map)
    {
        pair.second.PrepareForSelect();
        const int fd = pair.first;
#if !defined(__APPLE__) && !defined(_MSC_VER)
        lldbassert(fd < FD_SETSIZE);
        if (fd >= FD_SETSIZE)
        {
            error.SetErrorStringWithFormat("%i is too large for select()", fd);
            return error;
        }
#endif
        if (pair.second.read_set)
        {
            max_read_fd = std::max<int>(fd, max_read_fd);
            max_fd = std::max<int>(fd, max_fd);
        }
        if (pair.second.write_set)
        {
            max_write_fd = std::max<int>(fd, max_write_fd);
            max_fd = std::max<int>(fd, max_fd);
        }
        if (pair.second.error_set)
        {
            max_error_fd = std::max<int>(fd, max_error_fd);
            max_fd = std::max<int>(fd, max_fd);
        }
    }

    if (max_fd == -1)
    {
        error.SetErrorString("no valid file descriptors");
        return error;
    }

    const int nfds = max_fd + 1;
    fd_set *read_fdset_ptr = nullptr;
    fd_set *write_fdset_ptr = nullptr;
    fd_set *error_fdset_ptr = nullptr;
    //----------------------------------------------------------------------
    // Initialize and zero out the fdsets
    //----------------------------------------------------------------------
#if defined(__APPLE__)
    llvm::SmallVector<fd_set, 1> read_fdset;
    llvm::SmallVector<fd_set, 1> write_fdset;
    llvm::SmallVector<fd_set, 1> error_fdset;

    if (max_read_fd >= 0)
    {
        read_fdset.resize((nfds / FD_SETSIZE) + 1);
        read_fdset_ptr = read_fdset.data();
    }
    if (max_write_fd >= 0)
    {
        write_fdset.resize((nfds / FD_SETSIZE) + 1);
        write_fdset_ptr = write_fdset.data();
    }
    if (max_error_fd >= 0)
    {
        error_fdset.resize((nfds / FD_SETSIZE) + 1);
        error_fdset_ptr = error_fdset.data();
    }
    for (auto &fd_set : read_fdset)
        FD_ZERO(&fd_set);
    for (auto &fd_set : write_fdset)
        FD_ZERO(&fd_set);
    for (auto &fd_set : error_fdset)
        FD_ZERO(&fd_set);
#else
    fd_set read_fdset;
    fd_set write_fdset;
    fd_set error_fdset;

    if (max_read_fd >= 0)
    {
        FD_ZERO(&read_fdset);
        read_fdset_ptr = &read_fdset;
    }
    if (max_write_fd >= 0)
    {
        FD_ZERO(&write_fdset);
        write_fdset_ptr = &write_fdset;
    }
    if (max_error_fd >= 0)
    {
        FD_ZERO(&error_fdset);
        error_fdset_ptr = &error_fdset;
    }
#endif
    //----------------------------------------------------------------------
    // Set the FD bits in the fdsets for read/write/error
    //----------------------------------------------------------------------
    for (auto &pair : m_fd_map)
    {
        const int fd = pair.first;

        if (pair.second.read_set)
            FD_SET(fd, read_fdset_ptr);

        if (pair.second.write_set)
            FD_SET(fd, write_fdset_ptr);

        if (pair.second.error_set)
            FD_SET(fd, error_fdset_ptr);
    }

    //----------------------------------------------------------------------
    // Setup our timeout time value if needed
    //----------------------------------------------------------------------
    struct timeval *tv_ptr = nullptr;
    struct timeval tv = {0, 0};

    while (1)
    {
        using namespace std::chrono;
        //------------------------------------------------------------------
        // Setup out relative timeout based on the end time if we have one
        //------------------------------------------------------------------
        if (m_end_time.hasValue())
        {
            tv_ptr = &tv;
            const auto remaining_dur = duration_cast<microseconds>(m_end_time.getValue() - steady_clock::now());
            if (remaining_dur.count() > 0)
            {
                // Wait for a specific amount of time
                const auto dur_secs = duration_cast<seconds>(remaining_dur);
                const auto dur_usecs = remaining_dur % seconds(1);
                tv.tv_sec = dur_secs.count();
                tv.tv_usec = dur_usecs.count();
            }
            else
            {
                // Just poll once with no timeout
                tv.tv_sec = 0;
                tv.tv_usec = 0;
            }
        }
        const int num_set_fds = ::select(nfds, read_fdset_ptr, write_fdset_ptr, error_fdset_ptr, tv_ptr);
        if (num_set_fds < 0)
        {
            // We got an error
            error.SetErrorToErrno();
            if (error.GetError() == EINTR)
            {
                error.Clear();
                continue; // Keep calling select if we get EINTR
            }
            else
                return error;
        }
        else if (num_set_fds == 0)
        {
            // Timeout
            error.SetError(ETIMEDOUT, lldb::eErrorTypePOSIX);
            error.SetErrorString("timed out");
            return error;
        }
        else
        {
            // One or more descriptors were set, update the FDInfo::select_is_set mask
            // so users can ask the SelectHelper class so clients can call one of:

            for (auto &pair : m_fd_map)
            {
                const int fd = pair.first;

                if (pair.second.read_set)
                {
                    if (FD_ISSET(fd, read_fdset_ptr))
                        pair.second.read_is_set = true;
                }
                if (pair.second.write_set)
                {
                    if (FD_ISSET(fd, write_fdset_ptr))
                        pair.second.write_is_set = true;
                }
                if (pair.second.error_set)
                {
                    if (FD_ISSET(fd, error_fdset_ptr))
                        pair.second.error_is_set = true;
                }
            }
            break;
        }
    }
    return error;
}