cpl_spawn.cpp

/**********************************************************************
 *
 * Project:  CPL - Common Portability Library
 * Purpose:  Implement CPLSystem().
 * Author:   Even Rouault, <even dot rouault at spatialys.com>
 *
 **********************************************************************
 * Copyright (c) 2012-2013, Even Rouault <even dot rouault at spatialys.com>
 *
 * SPDX-License-Identifier: MIT
 ****************************************************************************/

#include "cpl_port.h"
#include "cpl_spawn.h"

#include <cstring>

#include "cpl_config.h"
#include "cpl_conv.h"
#include "cpl_error.h"
#include "cpl_multiproc.h"
#include "cpl_string.h"

#if defined(_WIN32)
#include <windows.h>
#else
#include <cassert>
#include <cerrno>
#include <csignal>
#include <cstdio>
#include <cstdlib>
#include <sys/types.h>
#include <sys/wait.h>
#include <unistd.h>
#ifdef HAVE_POSIX_SPAWNP
#include <spawn.h>
#ifdef __APPLE__
#include <TargetConditionals.h>
#endif
#if defined(__APPLE__) && (!defined(TARGET_OS_IPHONE) || TARGET_OS_IPHONE == 0)
#include <crt_externs.h>
#define environ (*_NSGetEnviron())
#else
#if defined(__FreeBSD__)
extern __attribute__((__weak__)) char **environ;
#else
extern char **environ;
#endif
#endif
#endif
#endif

constexpr int PIPE_BUFFER_SIZE = 4096;

constexpr int IN_FOR_PARENT = 0;
constexpr int OUT_FOR_PARENT = 1;

static void FillFileFromPipe(CPL_FILE_HANDLE pipe_fd, VSILFILE *fout);

/************************************************************************/
/*                        FillPipeFromFile()                            */
/************************************************************************/

static void FillPipeFromFile(VSILFILE *fin, CPL_FILE_HANDLE pipe_fd)
{
    char buf[PIPE_BUFFER_SIZE] = {};
    while (true)
    {
        const int nRead =
            static_cast<int>(VSIFReadL(buf, 1, PIPE_BUFFER_SIZE, fin));
        if (nRead <= 0)
            break;
        if (!CPLPipeWrite(pipe_fd, buf, nRead))
            break;
    }
}

/************************************************************************/
/*                            CPLSpawn()                                */
/************************************************************************/

/**
 * Runs an executable in another process.
 *
 * This function runs an executable, wait for it to finish and returns
 * its exit code.
 *
 * It is implemented as CreateProcess() on Windows platforms, and fork()/exec()
 * on other platforms.
 *
 * @param papszArgv argument list of the executable to run. papszArgv[0] is the
 *                  name of the executable
 * @param fin File handle for input data to feed to the standard input of the
 *            sub-process. May be NULL.
 * @param fout File handle for output data to extract from the standard output
 *            of the sub-process. May be NULL.
 * @param bDisplayErr Set to TRUE to emit the content of the standard error
 *                    stream of the sub-process with CPLError().
 *
 * @return the exit code of the spawned process, or -1 in case of error.
 *
 * @since GDAL 1.10.0
 */

int CPLSpawn(const char *const papszArgv[], VSILFILE *fin, VSILFILE *fout,
             int bDisplayErr)
{
    CPLSpawnedProcess *sp =
        CPLSpawnAsync(nullptr, papszArgv, TRUE, TRUE, TRUE, nullptr);
    if (sp == nullptr)
        return -1;

    CPL_FILE_HANDLE in_child = CPLSpawnAsyncGetOutputFileHandle(sp);
    if (fin != nullptr)
        FillPipeFromFile(fin, in_child);
    CPLSpawnAsyncCloseOutputFileHandle(sp);

    CPL_FILE_HANDLE out_child = CPLSpawnAsyncGetInputFileHandle(sp);
    if (fout != nullptr)
        FillFileFromPipe(out_child, fout);
    CPLSpawnAsyncCloseInputFileHandle(sp);

    CPL_FILE_HANDLE err_child = CPLSpawnAsyncGetErrorFileHandle(sp);
    CPLString osName;
    osName.Printf("/vsimem/child_stderr_" CPL_FRMT_GIB, CPLGetPID());
    VSILFILE *ferr = VSIFOpenL(osName.c_str(), "w");

    FillFileFromPipe(err_child, ferr);
    CPLSpawnAsyncCloseErrorFileHandle(sp);

    CPL_IGNORE_RET_VAL(VSIFCloseL(ferr));
    vsi_l_offset nDataLength = 0;
    GByte *pData = VSIGetMemFileBuffer(osName.c_str(), &nDataLength, TRUE);
    if (nDataLength > 0)
        pData[nDataLength - 1] = '\0';
    if (pData &&
        strstr(const_cast<const char *>(reinterpret_cast<char *>(pData)),
               "An error occurred while forking process") != nullptr)
        bDisplayErr = TRUE;
    if (pData && bDisplayErr)
        CPLError(CE_Failure, CPLE_AppDefined, "[%s error] %s", papszArgv[0],
                 pData);
    CPLFree(pData);

    return CPLSpawnAsyncFinish(sp, TRUE, FALSE);
}

#if defined(_WIN32)

/************************************************************************/
/*                          CPLPipeRead()                               */
/************************************************************************/

int CPLPipeRead(CPL_FILE_HANDLE fin, void *data, int length)
{
    GByte *pabyData = static_cast<GByte *>(data);
    int nRemain = length;
    while (nRemain > 0)
    {
        DWORD nRead = 0;
        if (!ReadFile(fin, pabyData, nRemain, &nRead, nullptr))
            return FALSE;
        pabyData += nRead;
        nRemain -= nRead;
    }
    return TRUE;
}

/************************************************************************/
/*                         CPLPipeWrite()                               */
/************************************************************************/

int CPLPipeWrite(CPL_FILE_HANDLE fout, const void *data, int length)
{
    const GByte *pabyData = static_cast<const GByte *>(data);
    int nRemain = length;
    while (nRemain > 0)
    {
        DWORD nWritten = 0;
        if (!WriteFile(fout, pabyData, nRemain, &nWritten, nullptr))
            return FALSE;
        pabyData += nWritten;
        nRemain -= nWritten;
    }
    return TRUE;
}

/************************************************************************/
/*                        FillFileFromPipe()                            */
/************************************************************************/

static void FillFileFromPipe(CPL_FILE_HANDLE pipe_fd, VSILFILE *fout)
{
    char buf[PIPE_BUFFER_SIZE] = {};
    while (true)
    {
        DWORD nRead = 0;
        if (!ReadFile(pipe_fd, buf, PIPE_BUFFER_SIZE, &nRead, nullptr))
            break;
        if (nRead <= 0)
            break;
        const int nWritten = static_cast<int>(VSIFWriteL(buf, 1, nRead, fout));
        if (nWritten < static_cast<int>(nRead))
            break;
    }
}

struct _CPLSpawnedProcess
{
    HANDLE hProcess;
    DWORD nProcessId;
    HANDLE hThread;
    CPL_FILE_HANDLE fin;
    CPL_FILE_HANDLE fout;
    CPL_FILE_HANDLE ferr;
};

/************************************************************************/
/*                            CPLSpawnAsync()                           */
/************************************************************************/

CPLSpawnedProcess *
CPLSpawnAsync(CPL_UNUSED int (*pfnMain)(CPL_FILE_HANDLE, CPL_FILE_HANDLE),
              const char *const papszArgv[], int bCreateInputPipe,
              int bCreateOutputPipe, int bCreateErrorPipe,
              char ** /* papszOptions */)
{
    if (papszArgv == nullptr)
    {
        CPLError(CE_Failure, CPLE_AppDefined,
                 "On Windows, papszArgv argument must not be NULL");
        return nullptr;
    }

    // TODO(schwehr): Consider initializing saAttr.
    SECURITY_ATTRIBUTES saAttr;
    saAttr.nLength = sizeof(SECURITY_ATTRIBUTES);
    saAttr.bInheritHandle = TRUE;
    saAttr.lpSecurityDescriptor = nullptr;

    // TODO(schwehr): Move these to where they are used after gotos are removed.
    HANDLE pipe_out[2] = {nullptr, nullptr};
    HANDLE pipe_err[2] = {nullptr, nullptr};
    CPLString osCommandLine;

    HANDLE pipe_in[2] = {nullptr, nullptr};
    if (bCreateInputPipe)
    {
        if (!CreatePipe(&pipe_in[IN_FOR_PARENT], &pipe_in[OUT_FOR_PARENT],
                        &saAttr, 0))
            goto err_pipe;
        // The child must not inherit from the write side of the pipe_in.
        if (!SetHandleInformation(pipe_in[OUT_FOR_PARENT], HANDLE_FLAG_INHERIT,
                                  0))
            goto err_pipe;
    }

    if (bCreateOutputPipe)
    {
        if (!CreatePipe(&pipe_out[IN_FOR_PARENT], &pipe_out[OUT_FOR_PARENT],
                        &saAttr, 0))
            goto err_pipe;
        // The child must not inherit from the read side of the pipe_out.
        if (!SetHandleInformation(pipe_out[IN_FOR_PARENT], HANDLE_FLAG_INHERIT,
                                  0))
            goto err_pipe;
    }

    if (bCreateErrorPipe)
    {
        if (!CreatePipe(&pipe_err[IN_FOR_PARENT], &pipe_err[OUT_FOR_PARENT],
                        &saAttr, 0))
            goto err_pipe;
        // The child must not inherit from the read side of the pipe_err.
        if (!SetHandleInformation(pipe_err[IN_FOR_PARENT], HANDLE_FLAG_INHERIT,
                                  0))
            goto err_pipe;
    }

    // TODO(schwehr): Consider initializing piProcInfo.
    PROCESS_INFORMATION piProcInfo;
    memset(&piProcInfo, 0, sizeof(PROCESS_INFORMATION));
    STARTUPINFO siStartInfo;
    memset(&siStartInfo, 0, sizeof(STARTUPINFO));
    siStartInfo.cb = sizeof(STARTUPINFO);
    siStartInfo.hStdInput = bCreateInputPipe ? pipe_in[IN_FOR_PARENT]
                                             : GetStdHandle(STD_INPUT_HANDLE);
    siStartInfo.hStdOutput = bCreateOutputPipe
                                 ? pipe_out[OUT_FOR_PARENT]
                                 : GetStdHandle(STD_OUTPUT_HANDLE);
    siStartInfo.hStdError = bCreateErrorPipe ? pipe_err[OUT_FOR_PARENT]
                                             : GetStdHandle(STD_ERROR_HANDLE);
    siStartInfo.dwFlags |= STARTF_USESTDHANDLES;

    for (int i = 0; papszArgv[i] != nullptr; i++)
    {
        if (i > 0)
            osCommandLine += " ";
        // We need to quote arguments with spaces in them (if not already done).
        if (strchr(papszArgv[i], ' ') != nullptr && papszArgv[i][0] != '"')
        {
            osCommandLine += "\"";
            osCommandLine += papszArgv[i];
            osCommandLine += "\"";
        }
        else
        {
            osCommandLine += papszArgv[i];
        }
    }

    if (!CreateProcess(nullptr, const_cast<CHAR *>(osCommandLine.c_str()),
                       nullptr,  // Process security attributes
                       nullptr,  // Primary thread security attributes
                       TRUE,     // Handles are inherited
                       CREATE_NO_WINDOW |
                           NORMAL_PRIORITY_CLASS,  // Creation flags
                       nullptr,                    // Use parent's environment
                       nullptr,  // Use parent's current directory
                       &siStartInfo, &piProcInfo))
    {
        CPLError(CE_Failure, CPLE_AppDefined, "Could not create process %s",
                 osCommandLine.c_str());
        goto err;
    }

    // Close unused end of pipe.
    if (bCreateInputPipe)
        CloseHandle(pipe_in[IN_FOR_PARENT]);
    if (bCreateOutputPipe)
        CloseHandle(pipe_out[OUT_FOR_PARENT]);
    if (bCreateErrorPipe)
        CloseHandle(pipe_err[OUT_FOR_PARENT]);

    {
        CPLSpawnedProcess *p = static_cast<CPLSpawnedProcess *>(
            CPLMalloc(sizeof(CPLSpawnedProcess)));
        p->hProcess = piProcInfo.hProcess;
        p->nProcessId = piProcInfo.dwProcessId;
        p->hThread = piProcInfo.hThread;
        p->fin = pipe_out[IN_FOR_PARENT];
        p->fout = pipe_in[OUT_FOR_PARENT];
        p->ferr = pipe_err[IN_FOR_PARENT];

        return p;
    }

err_pipe:
    CPLError(CE_Failure, CPLE_AppDefined, "Could not create pipe");
err:
    for (int i = 0; i < 2; i++)
    {
        if (pipe_in[i] != nullptr)
            CloseHandle(pipe_in[i]);
        if (pipe_out[i] != nullptr)
            CloseHandle(pipe_out[i]);
        if (pipe_err[i] != nullptr)
            CloseHandle(pipe_err[i]);
    }

    return nullptr;
}

/************************************************************************/
/*                  CPLSpawnAsyncGetChildProcessId()                    */
/************************************************************************/

CPL_PID CPLSpawnAsyncGetChildProcessId(CPLSpawnedProcess *p)
{
    return p->nProcessId;
}

/************************************************************************/
/*                        CPLSpawnAsyncFinish()                         */
/************************************************************************/

int CPLSpawnAsyncFinish(CPLSpawnedProcess *p, int bWait, int /* bKill */)
{
    // Get the exit code.
    DWORD exitCode = -1;

    if (bWait)
    {
        WaitForSingleObject(p->hProcess, INFINITE);
        GetExitCodeProcess(p->hProcess, &exitCode);
    }
    else
    {
        exitCode = 0;
    }

    CloseHandle(p->hProcess);
    CloseHandle(p->hThread);

    CPLSpawnAsyncCloseInputFileHandle(p);
    CPLSpawnAsyncCloseOutputFileHandle(p);
    CPLSpawnAsyncCloseErrorFileHandle(p);
    CPLFree(p);

    return static_cast<int>(exitCode);
}

/************************************************************************/
/*                 CPLSpawnAsyncCloseInputFileHandle()                  */
/************************************************************************/

void CPLSpawnAsyncCloseInputFileHandle(CPLSpawnedProcess *p)
{
    if (p->fin != nullptr)
        CloseHandle(p->fin);
    p->fin = nullptr;
}

/************************************************************************/
/*                 CPLSpawnAsyncCloseOutputFileHandle()                 */
/************************************************************************/

void CPLSpawnAsyncCloseOutputFileHandle(CPLSpawnedProcess *p)
{
    if (p->fout != nullptr)
        CloseHandle(p->fout);
    p->fout = nullptr;
}

/************************************************************************/
/*                 CPLSpawnAsyncCloseErrorFileHandle()                  */
/************************************************************************/

void CPLSpawnAsyncCloseErrorFileHandle(CPLSpawnedProcess *p)
{
    if (p->ferr != nullptr)
        CloseHandle(p->ferr);
    p->ferr = nullptr;
}

#else  // Not WIN32

/************************************************************************/
/*                          CPLPipeRead()                               */
/************************************************************************/

/**
 * Read data from the standard output of a forked process.
 *
 * @param fin handle returned by CPLSpawnAsyncGetInputFileHandle().
 * @param data buffer in which to write.
 * @param length number of bytes to read.
 *
 * @return TRUE in case of success.
 *
 * @since GDAL 1.10.0
 */
int CPLPipeRead(CPL_FILE_HANDLE fin, void *data, int length)
{
    GByte *pabyData = static_cast<GByte *>(data);
    int nRemain = length;
    while (nRemain > 0)
    {
        while (true)
        {
            // coverity[overflow_sink]
            const ssize_t n = read(fin, pabyData, nRemain);
            if (n < 0)
            {
                if (errno == EINTR)
                    continue;
                else
                    return FALSE;
            }
            else if (n == 0)
                return FALSE;
            pabyData += n;
            nRemain -= static_cast<int>(n);
            break;
        }
    }
    return TRUE;
}

/************************************************************************/
/*                          CPLPipeWrite()                              */
/************************************************************************/

/**
 * Write data to the standard input of a forked process.
 *
 * @param fout handle returned by CPLSpawnAsyncGetOutputFileHandle().
 * @param data buffer from which to read.
 * @param length number of bytes to write.
 *
 * @return TRUE in case of success.
 *
 * @since GDAL 1.10.0
 */
int CPLPipeWrite(CPL_FILE_HANDLE fout, const void *data, int length)
{
    const GByte *pabyData = static_cast<const GByte *>(data);
    int nRemain = length;
    while (nRemain > 0)
    {
        while (true)
        {
            // coverity[overflow_sink]
            const ssize_t n = write(fout, pabyData, nRemain);
            if (n < 0)
            {
                if (errno == EINTR)
                    continue;
                else
                    return FALSE;
            }
            pabyData += n;
            nRemain -= static_cast<int>(n);
            break;
        }
    }
    return TRUE;
}

/************************************************************************/
/*                          FillFileFromPipe()                              */
/************************************************************************/

static void FillFileFromPipe(CPL_FILE_HANDLE pipe_fd, VSILFILE *fout)
{
    char buf[PIPE_BUFFER_SIZE] = {};
    while (true)
    {
        const int nRead =
            static_cast<int>(read(pipe_fd, buf, PIPE_BUFFER_SIZE));
        if (nRead <= 0)
            break;
        const int nWritten = static_cast<int>(VSIFWriteL(buf, 1, nRead, fout));
        if (nWritten < nRead)
            break;
    }
}

/************************************************************************/
/*                            CPLSpawnAsync()                           */
/************************************************************************/

struct _CPLSpawnedProcess
{
    pid_t pid;
    CPL_FILE_HANDLE fin;
    CPL_FILE_HANDLE fout;
    CPL_FILE_HANDLE ferr;
#ifdef HAVE_POSIX_SPAWNP
    bool bFreeActions;
    posix_spawn_file_actions_t actions;
#endif
};

/**
 * Runs an executable in another process (or fork the current process)
 * and return immediately.
 *
 * This function launches an executable and returns immediately, while letting
 * the sub-process to run asynchronously.
 *
 * It is implemented as CreateProcess() on Windows platforms, and fork()/exec()
 * on other platforms.
 *
 * On Unix, a pointer of function can be provided to run in the child process,
 * without exec()'ing a new executable.
 *
 * @param pfnMain the function to run in the child process (Unix only).
 * @param papszArgv argument list of the executable to run. papszArgv[0] is the
 *                  name of the executable.
 * @param bCreateInputPipe set to TRUE to create a pipe for the child
 * input stream.
 * @param bCreateOutputPipe set to TRUE to create a pipe for the child
 * output stream.
 * @param bCreateErrorPipe set to TRUE to create a pipe for the child
 * error stream.
 * @param papszOptions unused. should be set to NULL.
 *
 * @return a handle, that must be freed with CPLSpawnAsyncFinish()
 *
 * @since GDAL 1.10.0
 */
CPLSpawnedProcess *
CPLSpawnAsync(int (*pfnMain)(CPL_FILE_HANDLE, CPL_FILE_HANDLE),
              const char *const papszArgv[], int bCreateInputPipe,
              int bCreateOutputPipe, int bCreateErrorPipe,
              CPL_UNUSED char **papszOptions)
{
    int pipe_in[2] = {-1, -1};
    int pipe_out[2] = {-1, -1};
    int pipe_err[2] = {-1, -1};

    if ((bCreateInputPipe && pipe(pipe_in)) ||
        (bCreateOutputPipe && pipe(pipe_out)) ||
        (bCreateErrorPipe && pipe(pipe_err)))
    {
        CPLError(CE_Failure, CPLE_AppDefined, "Could not create pipe");
        return nullptr;
    }

    bool bDup2In = CPL_TO_BOOL(bCreateInputPipe);
    bool bDup2Out = CPL_TO_BOOL(bCreateOutputPipe);
    bool bDup2Err = CPL_TO_BOOL(bCreateErrorPipe);

    char **papszArgvDup = CSLDuplicate(const_cast<char **>(papszArgv));

    // If we don't do any file actions, posix_spawnp() might be implemented
    // efficiently as a vfork()/exec() pair (or if it is not available, we
    // can use vfork()/exec()), so if the child is cooperative
    // we pass the pipe handles as commandline arguments.
    if (papszArgv != nullptr)
    {
        for (int i = 0; papszArgvDup[i] != nullptr; i++)
        {
            if (bCreateInputPipe && strcmp(papszArgvDup[i], "{pipe_in}") == 0)
            {
                CPLFree(papszArgvDup[i]);
                papszArgvDup[i] = CPLStrdup(CPLSPrintf(
                    "%d,%d", pipe_in[IN_FOR_PARENT], pipe_in[OUT_FOR_PARENT]));
                bDup2In = false;
            }
            else if (bCreateOutputPipe &&
                     strcmp(papszArgvDup[i], "{pipe_out}") == 0)
            {
                CPLFree(papszArgvDup[i]);
                papszArgvDup[i] =
                    CPLStrdup(CPLSPrintf("%d,%d", pipe_out[OUT_FOR_PARENT],
                                         pipe_out[IN_FOR_PARENT]));
                bDup2Out = false;
            }
            else if (bCreateErrorPipe &&
                     strcmp(papszArgvDup[i], "{pipe_err}") == 0)
            {
                CPLFree(papszArgvDup[i]);
                papszArgvDup[i] =
                    CPLStrdup(CPLSPrintf("%d,%d", pipe_err[OUT_FOR_PARENT],
                                         pipe_err[IN_FOR_PARENT]));
                bDup2Err = false;
            }
        }
    }

#ifdef HAVE_POSIX_SPAWNP
    if (papszArgv != nullptr)
    {
        bool bHasActions = false;
        posix_spawn_file_actions_t actions;

        if (bDup2In)
        {
            /*if( !bHasActions )*/ posix_spawn_file_actions_init(&actions);
            posix_spawn_file_actions_adddup2(&actions, pipe_in[IN_FOR_PARENT],
                                             fileno(stdin));
            posix_spawn_file_actions_addclose(&actions,
                                              pipe_in[OUT_FOR_PARENT]);
            bHasActions = true;
        }

        if (bDup2Out)
        {
            if (!bHasActions)
                posix_spawn_file_actions_init(&actions);
            posix_spawn_file_actions_adddup2(&actions, pipe_out[OUT_FOR_PARENT],
                                             fileno(stdout));
            posix_spawn_file_actions_addclose(&actions,
                                              pipe_out[IN_FOR_PARENT]);
            bHasActions = true;
        }

        if (bDup2Err)
        {
            if (!bHasActions)
                posix_spawn_file_actions_init(&actions);
            posix_spawn_file_actions_adddup2(&actions, pipe_err[OUT_FOR_PARENT],
                                             fileno(stderr));
            posix_spawn_file_actions_addclose(&actions,
                                              pipe_err[IN_FOR_PARENT]);
            bHasActions = true;
        }

        pid_t pid = 0;
        assert(papszArgvDup[0] != nullptr);
        if (posix_spawnp(&pid, papszArgvDup[0],
                         bHasActions ? &actions : nullptr, nullptr,
                         papszArgvDup, environ) != 0)
        {
            if (bHasActions)
                posix_spawn_file_actions_destroy(&actions);
            CPLError(CE_Failure, CPLE_AppDefined, "posix_spawnp() failed");
            CSLDestroy(papszArgvDup);
            for (int i = 0; i < 2; i++)
            {
                if (pipe_in[i] >= 0)
                    close(pipe_in[i]);
                if (pipe_out[i] >= 0)
                    close(pipe_out[i]);
                if (pipe_err[i] >= 0)
                    close(pipe_err[i]);
            }

            return nullptr;
        }

        CSLDestroy(papszArgvDup);

        // Close unused end of pipe.
        if (bCreateInputPipe)
            close(pipe_in[IN_FOR_PARENT]);
        if (bCreateOutputPipe)
            close(pipe_out[OUT_FOR_PARENT]);
        if (bCreateErrorPipe)
            close(pipe_err[OUT_FOR_PARENT]);

            // Ignore SIGPIPE.
#ifdef SIGPIPE
        std::signal(SIGPIPE, SIG_IGN);
#endif
        CPLSpawnedProcess *p = static_cast<CPLSpawnedProcess *>(
            CPLMalloc(sizeof(CPLSpawnedProcess)));
        if (bHasActions)
            memcpy(&p->actions, &actions, sizeof(actions));
        p->bFreeActions = bHasActions;
        p->pid = pid;
        p->fin = pipe_out[IN_FOR_PARENT];
        p->fout = pipe_in[OUT_FOR_PARENT];
        p->ferr = pipe_err[IN_FOR_PARENT];
        return p;
    }
#endif  // #ifdef HAVE_POSIX_SPAWNP

    pid_t pid = 0;

#if defined(HAVE_VFORK) && !defined(HAVE_POSIX_SPAWNP)
    if (papszArgv != nullptr && !bDup2In && !bDup2Out && !bDup2Err)
    {
        // Workaround clang static analyzer warning about unsafe use of vfork.
        pid_t (*p_vfork)(void) = vfork;
        pid = p_vfork();
    }
    else
#endif
    {
        pid = fork();
    }

    if (pid == 0)
    {
        // Close unused end of pipe.
        if (bDup2In)
            close(pipe_in[OUT_FOR_PARENT]);
        if (bDup2Out)
            close(pipe_out[IN_FOR_PARENT]);
        if (bDup2Err)
            close(pipe_err[IN_FOR_PARENT]);

#ifndef HAVE_POSIX_SPAWNP
        if (papszArgv != nullptr)
        {
            if (bDup2In)
                dup2(pipe_in[IN_FOR_PARENT], fileno(stdin));
            if (bDup2Out)
                dup2(pipe_out[OUT_FOR_PARENT], fileno(stdout));
            if (bDup2Err)
                dup2(pipe_err[OUT_FOR_PARENT], fileno(stderr));

            execvp(papszArgvDup[0], papszArgvDup);

            _exit(1);
        }
        else
#endif  // HAVE_POSIX_SPAWNP
        {
            if (bCreateErrorPipe)
                close(pipe_err[OUT_FOR_PARENT]);

            int nRet = 0;
            if (pfnMain != nullptr)
                nRet = pfnMain(bCreateInputPipe ? pipe_in[IN_FOR_PARENT]
                                                : fileno(stdin),
                               bCreateOutputPipe ? pipe_out[OUT_FOR_PARENT]
                                                 : fileno(stdout));
            _exit(nRet);
        }
    }
    else if (pid > 0)
    {
        CSLDestroy(papszArgvDup);

        // Close unused end of pipe.
        if (bCreateInputPipe)
            close(pipe_in[IN_FOR_PARENT]);
        if (bCreateOutputPipe)
            close(pipe_out[OUT_FOR_PARENT]);
        if (bCreateErrorPipe)
            close(pipe_err[OUT_FOR_PARENT]);

            // Ignore SIGPIPE.
#ifdef SIGPIPE
        std::signal(SIGPIPE, SIG_IGN);
#endif
        CPLSpawnedProcess *p = static_cast<CPLSpawnedProcess *>(
            CPLMalloc(sizeof(CPLSpawnedProcess)));
#ifdef HAVE_POSIX_SPAWNP
        p->bFreeActions = false;
#endif
        p->pid = pid;
        p->fin = pipe_out[IN_FOR_PARENT];
        p->fout = pipe_in[OUT_FOR_PARENT];
        p->ferr = pipe_err[IN_FOR_PARENT];
        return p;
    }

    CPLError(CE_Failure, CPLE_AppDefined, "Fork failed");

    CSLDestroy(papszArgvDup);
    for (int i = 0; i < 2; i++)
    {
        if (pipe_in[i] >= 0)
            close(pipe_in[i]);
        if (pipe_out[i] >= 0)
            close(pipe_out[i]);
        if (pipe_err[i] >= 0)
            close(pipe_err[i]);
    }

    return nullptr;
}

/************************************************************************/
/*                  CPLSpawnAsyncGetChildProcessId()                    */
/************************************************************************/

CPL_PID CPLSpawnAsyncGetChildProcessId(CPLSpawnedProcess *p)
{
    return p->pid;
}

/************************************************************************/
/*                        CPLSpawnAsyncFinish()                         */
/************************************************************************/

/**
 * \fn CPLSpawnAsyncFinish(CPLSpawnedProcess*,int,int)
 * Wait for the forked process to finish.
 *
 * @param p handle returned by CPLSpawnAsync()
 * @param bWait set to TRUE to wait for the child to terminate. Otherwise the
 *              associated handles are just cleaned.
 * @param bKill set to TRUE to force child termination (unimplemented right
 *              now).
 *
 * @return the return code of the forked process if bWait == TRUE, 0 otherwise
 *
 * @since GDAL 1.10.0
 */

int CPLSpawnAsyncFinish(CPLSpawnedProcess *p, int bWait, CPL_UNUSED int bKill)
{
    int status = 0;

    if (bWait)
    {
        while (true)
        {
            status = -1;
            const int ret = waitpid(p->pid, &status, 0);
            if (ret < 0)
            {
                if (errno != EINTR)
                {
                    break;
                }
            }
            else
            {
                if (WIFEXITED(status))
                {
                    status = WEXITSTATUS(status);
                }
                else
                {
                    status = -1;
                }
                break;
            }
        }
    }

    CPLSpawnAsyncCloseInputFileHandle(p);
    CPLSpawnAsyncCloseOutputFileHandle(p);
    CPLSpawnAsyncCloseErrorFileHandle(p);
#ifdef HAVE_POSIX_SPAWNP
    if (p->bFreeActions)
        posix_spawn_file_actions_destroy(&p->actions);
#endif
    CPLFree(p);
    return status;
}

/************************************************************************/
/*                 CPLSpawnAsyncCloseInputFileHandle()                  */
/************************************************************************/

void CPLSpawnAsyncCloseInputFileHandle(CPLSpawnedProcess *p)
{
    if (p->fin >= 0)
        close(p->fin);
    p->fin = -1;
}

/************************************************************************/
/*                 CPLSpawnAsyncCloseOutputFileHandle()                 */
/************************************************************************/

void CPLSpawnAsyncCloseOutputFileHandle(CPLSpawnedProcess *p)
{
    if (p->fout >= 0)
        close(p->fout);
    p->fout = -1;
}

/************************************************************************/
/*                 CPLSpawnAsyncCloseErrorFileHandle()                  */
/************************************************************************/

void CPLSpawnAsyncCloseErrorFileHandle(CPLSpawnedProcess *p)
{
    if (p->ferr >= 0)
        close(p->ferr);
    p->ferr = -1;
}

#endif

/************************************************************************/
/*                    CPLSpawnAsyncGetInputFileHandle()                 */
/************************************************************************/

/**
 * Return the file handle of the standard output of the forked process
 * from which to read.
 *
 * @param p handle returned by CPLSpawnAsync().
 *
 * @return the file handle.
 *
 * @since GDAL 1.10.0
 */
CPL_FILE_HANDLE CPLSpawnAsyncGetInputFileHandle(CPLSpawnedProcess *p)
{
    return p->fin;
}

/************************************************************************/
/*                   CPLSpawnAsyncGetOutputFileHandle()                 */
/************************************************************************/

/**
 * Return the file handle of the standard input of the forked process
 * into which to write
 *
 * @param p handle returned by CPLSpawnAsync().
 *
 * @return the file handle.
 *
 * @since GDAL 1.10.0
 */
CPL_FILE_HANDLE CPLSpawnAsyncGetOutputFileHandle(CPLSpawnedProcess *p)
{
    return p->fout;
}

/************************************************************************/
/*                    CPLSpawnAsyncGetErrorFileHandle()                 */
/************************************************************************/

/**
 * Return the file handle of the standard error of the forked process
 * from which to read.
 *
 * @param p handle returned by CPLSpawnAsync().
 *
 * @return the file handle
 *
 * @since GDAL 1.10.0
 */
CPL_FILE_HANDLE CPLSpawnAsyncGetErrorFileHandle(CPLSpawnedProcess *p)
{
    return p->ferr;
}