openfoam/src/OSspecific/POSIX/POSIX.C

/*---------------------------------------------------------------------------*\
  =========                 |
  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
   \\    /   O peration     |
    \\  /    A nd           | Copyright (C) 2011-2016 OpenFOAM Foundation
     \\/     M anipulation  | Copyright (C) 2016 OpenCFD Ltd.
-------------------------------------------------------------------------------
License
    This file is part of OpenFOAM.

    OpenFOAM is free software: you can redistribute it and/or modify it
    under the terms of the GNU General Public License as published by
    the Free Software Foundation, either version 3 of the License, or
    (at your option) any later version.

    OpenFOAM is distributed in the hope that it will be useful, but WITHOUT
    ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
    FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
    for more details.

    You should have received a copy of the GNU General Public License
    along with OpenFOAM.  If not, see <http://www.gnu.org/licenses/>.

Description
    POSIX versions of the functions declared in OSspecific.H

\*---------------------------------------------------------------------------*/

#ifdef solarisGcc
    #define _SYS_VNODE_H
#endif

#include "OSspecific.H"
#include "POSIX.H"
#include "foamVersion.H"
#include "fileName.H"
#include "fileStat.H"
#include "timer.H"
#include "IFstream.H"
#include "DynamicList.H"
#include "CStringList.H"
#include "SubList.H"

#include <fstream>
#include <cstdlib>
#include <cctype>

#include <stdio.h>
#include <unistd.h>
#include <dirent.h>
#include <pwd.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <sys/stat.h>
#include <sys/socket.h>
#include <netdb.h>
#include <dlfcn.h>
#include <link.h>

#include <netinet/in.h>

#ifdef USE_RANDOM
    #include <climits>
    #if INT_MAX    != 2147483647
        #error "INT_MAX    != 2147483647"
        #error "The random number generator may not work!"
    #endif
#endif

// * * * * * * * * * * * * * * Static Data Members * * * * * * * * * * * * * //

namespace Foam
{
    defineTypeNameAndDebug(POSIX, 0);
}


// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

pid_t Foam::pid()
{
    return ::getpid();
}


pid_t Foam::ppid()
{
    return ::getppid();
}


pid_t Foam::pgid()
{
    return ::getpgrp();
}


bool Foam::env(const word& envName)
{
    return ::getenv(envName.c_str()) != NULL;
}


Foam::string Foam::getEnv(const word& envName)
{
    char* env = ::getenv(envName.c_str());

    if (env)
    {
        return string(env);
    }
    else
    {
        // Return null-constructed string rather than string::null
        // to avoid cyclic dependencies in the construction of globals
        return string();
    }
}


bool Foam::setEnv
(
    const word& envName,
    const std::string& value,
    const bool overwrite
)
{
    return setenv(envName.c_str(), value.c_str(), overwrite) == 0;
}


Foam::string Foam::hostName(bool full)
{
    char buf[128];
    ::gethostname(buf, sizeof(buf));

    // implementation as per hostname from net-tools
    if (full)
    {
        struct hostent *hp = ::gethostbyname(buf);
        if (hp)
        {
            return hp->h_name;
        }
    }

    return buf;
}


Foam::string Foam::domainName()
{
    char buf[128];
    ::gethostname(buf, sizeof(buf));

    // implementation as per hostname from net-tools
    struct hostent *hp = ::gethostbyname(buf);
    if (hp)
    {
        char *p = ::strchr(hp->h_name, '.');
        if (p)
        {
            ++p;
            return p;
        }
    }

    return string::null;
}


Foam::string Foam::userName()
{
    struct passwd* pw = ::getpwuid(::getuid());

    if (pw != NULL)
    {
        return pw->pw_name;
    }
    else
    {
        return string::null;
    }
}


bool Foam::isAdministrator()
{
    return (::geteuid() == 0);
}


Foam::fileName Foam::home()
{
    char* env = ::getenv("HOME");

    if (env != NULL)
    {
        return fileName(env);
    }
    else
    {
        struct passwd* pw = ::getpwuid(getuid());

        if (pw != NULL)
        {
            return pw->pw_dir;
        }
        else
        {
            return fileName::null;
        }
    }
}


Foam::fileName Foam::home(const string& userName)
{
    struct passwd* pw;

    if (userName.size())
    {
        pw = ::getpwnam(userName.c_str());
    }
    else
    {
        char* env = ::getenv("HOME");

        if (env != NULL)
        {
            return fileName(env);
        }

        pw = ::getpwuid(::getuid());
    }

    if (pw != NULL)
    {
        return pw->pw_dir;
    }
    else
    {
        return fileName::null;
    }
}


Foam::fileName Foam::cwd()
{
    label pathLengthLimit = POSIX::pathLengthChunk;
    List<char> path(pathLengthLimit);

    // Resize path if getcwd fails with an ERANGE error
    while(pathLengthLimit == path.size())
    {
        if (::getcwd(path.data(), path.size()))
        {
            return path.data();
        }
        else if(errno == ERANGE)
        {
            // Increment path length upto the pathLengthMax limit
            if
            (
                (pathLengthLimit += POSIX::pathLengthChunk)
             >= POSIX::pathLengthMax
            )
            {
                FatalErrorInFunction
                    << "Attempt to increase path length beyond limit of "
                    << POSIX::pathLengthMax
                    << exit(FatalError);
            }

            path.setSize(pathLengthLimit);
        }
        else
        {
            break;
        }
    }

    FatalErrorInFunction
        << "Couldn't get the current working directory"
        << exit(FatalError);

    return fileName::null;
}


bool Foam::chDir(const fileName& dir)
{
    return ::chdir(dir.c_str()) == 0;
}


Foam::fileNameList Foam::findEtcFiles
(
    const fileName& name,
    bool mandatory,
    bool findFirst
)
{
    fileNameList results;

    // Search for user files in
    // * ~/.OpenFOAM/VERSION
    // * ~/.OpenFOAM
    //
    fileName searchDir = home()/".OpenFOAM";
    if (isDir(searchDir))
    {
        fileName fullName = searchDir/FOAMversion/name;
        if (isFile(fullName))
        {
            results.append(fullName);
            if (findFirst)
            {
                return results;
            }
        }

        fullName = searchDir/name;
        if (isFile(fullName))
        {
            results.append(fullName);
            if (findFirst)
            {
                return results;
            }
        }
    }

    // Search for group (site) files in
    // * $WM_PROJECT_SITE/VERSION
    // * $WM_PROJECT_SITE
    //
    searchDir = getEnv("WM_PROJECT_SITE");
    if (searchDir.size())
    {
        if (isDir(searchDir))
        {
            fileName fullName = searchDir/FOAMversion/name;
            if (isFile(fullName))
            {
                results.append(fullName);
                if (findFirst)
                {
                    return results;
                }
            }

            fullName = searchDir/name;
            if (isFile(fullName))
            {
                results.append(fullName);
                if (findFirst)
                {
                    return results;
                }
            }
        }
    }
    else
    {
        // OR search for group (site) files in
        // * $WM_PROJECT_INST_DIR/site/VERSION
        // * $WM_PROJECT_INST_DIR/site
        //
        searchDir = getEnv("WM_PROJECT_INST_DIR");
        if (isDir(searchDir))
        {
            fileName fullName = searchDir/"site"/FOAMversion/name;
            if (isFile(fullName))
            {
                results.append(fullName);
                if (findFirst)
                {
                    return results;
                }
            }

            fullName = searchDir/"site"/name;
            if (isFile(fullName))
            {
                results.append(fullName);
                if (findFirst)
                {
                    return results;
                }
            }
        }
    }

    // Search for other (shipped) files in
    // * $WM_PROJECT_DIR/etc
    //
    searchDir = getEnv("WM_PROJECT_DIR");
    if (isDir(searchDir))
    {
        fileName fullName = searchDir/"etc"/name;
        if (isFile(fullName))
        {
            results.append(fullName);
            if (findFirst)
            {
                return results;
            }
        }
    }

    // Not found
    if (results.empty())
    {
        // Abort if the file is mandatory, otherwise return null
        if (mandatory)
        {
            std::cerr
                << "--> FOAM FATAL ERROR in Foam::findEtcFiles() :"
                   " could not find mandatory file\n    '"
                << name.c_str() << "'\n\n" << std::endl;
            ::exit(1);
        }
    }

    // Return list of matching paths or empty list if none found
    return results;
}


Foam::fileName Foam::findEtcFile(const fileName& name, bool mandatory)
{
    fileNameList results(findEtcFiles(name, mandatory, true));

    if (results.size())
    {
        return results[0];
    }
    else
    {
        return fileName();
    }
}


bool Foam::mkDir(const fileName& pathName, mode_t mode)
{
    // empty names are meaningless
    if (pathName.empty())
    {
        return false;
    }

    // Construct instance path directory if does not exist
    if (::mkdir(pathName.c_str(), mode) == 0)
    {
        // Directory made OK so return true
        return true;
    }
    else
    {
        switch (errno)
        {
            case EPERM:
            {
                FatalErrorInFunction
                    << "The filesystem containing " << pathName
                    << " does not support the creation of directories."
                    << exit(FatalError);

                return false;
            }

            case EEXIST:
            {
                // Directory already exists so simply return true
                return true;
            }

            case EFAULT:
            {
                FatalErrorInFunction
                    << "" << pathName
                    << " points outside your accessible address space."
                    << exit(FatalError);

                return false;
            }

            case EACCES:
            {
                FatalErrorInFunction
                    << "The parent directory does not allow write "
                       "permission to the process,"<< nl
                    << "or one of the directories in " << pathName
                    << " did not allow search (execute) permission."
                    << exit(FatalError);

                return false;
            }

            case ENAMETOOLONG:
            {
                FatalErrorInFunction
                    << "" << pathName << " is too long."
                    << exit(FatalError);

                return false;
            }

            case ENOENT:
            {
                // Part of the path does not exist so try to create it
                if (pathName.path().size() && mkDir(pathName.path(), mode))
                {
                    return mkDir(pathName, mode);
                }
                else
                {
                    FatalErrorInFunction
                        << "Couldn't create directory " << pathName
                        << exit(FatalError);

                    return false;
                }
            }

            case ENOTDIR:
            {
                FatalErrorInFunction
                    << "A component used as a directory in " << pathName
                    << " is not, in fact, a directory."
                    << exit(FatalError);

                return false;
            }

            case ENOMEM:
            {
                FatalErrorInFunction
                    << "Insufficient kernel memory was available to make "
                       "directory " << pathName << '.'
                    << exit(FatalError);

                return false;
            }

            case EROFS:
            {
                FatalErrorInFunction
                    << "" << pathName
                    << " refers to a file on a read-only filesystem."
                    << exit(FatalError);

                return false;
            }

            case ELOOP:
            {
                FatalErrorInFunction
                    << "Too many symbolic links were encountered in resolving "
                    << pathName << '.'
                    << exit(FatalError);

                return false;
            }

            case ENOSPC:
            {
                FatalErrorInFunction
                    << "The device containing " << pathName
                    << " has no room for the new directory or "
                    << "the user's disk quota is exhausted."
                    << exit(FatalError);

                return false;
            }

            default:
            {
                FatalErrorInFunction
                    << "Couldn't create directory " << pathName
                    << exit(FatalError);

                return false;
            }
        }
    }
}


bool Foam::chMod(const fileName& name, const mode_t m)
{
    return ::chmod(name.c_str(), m) == 0;
}


mode_t Foam::mode(const fileName& name, const bool followLink)
{
    fileStat fileStatus(name, followLink);
    if (fileStatus.isValid())
    {
        return fileStatus.status().st_mode;
    }
    else
    {
        return 0;
    }
}


Foam::fileName::Type Foam::type(const fileName& name, const bool followLink)
{
    mode_t m = mode(name, followLink);

    if (S_ISREG(m))
    {
        return fileName::FILE;
    }
    else if (S_ISLNK(m))
    {
        return fileName::LINK;
    }
    else if (S_ISDIR(m))
    {
        return fileName::DIRECTORY;
    }
    else
    {
        return fileName::UNDEFINED;
    }
}


bool Foam::exists
(
    const fileName& name,
    const bool checkGzip,
    const bool followLink
)
{
    return mode(name, followLink) || isFile(name, checkGzip, followLink);
}


bool Foam::isDir(const fileName& name, const bool followLink)
{
    return S_ISDIR(mode(name, followLink));
}


bool Foam::isFile
(
    const fileName& name,
    const bool checkGzip,
    const bool followLink
)
{
    return
        S_ISREG(mode(name, followLink))
     || (checkGzip && S_ISREG(mode(name + ".gz", followLink)));
}


off_t Foam::fileSize(const fileName& name, const bool followLink)
{
    fileStat fileStatus(name, followLink);
    if (fileStatus.isValid())
    {
        return fileStatus.status().st_size;
    }
    else
    {
        return -1;
    }
}


time_t Foam::lastModified(const fileName& name, const bool followLink)
{
    fileStat fileStatus(name, followLink);
    if (fileStatus.isValid())
    {
        return fileStatus.status().st_mtime;
    }
    else
    {
        return 0;
    }
}


Foam::fileNameList Foam::readDir
(
    const fileName& directory,
    const fileName::Type type,
    const bool filtergz,
    const bool followLink
)
{
    // Initial filename list size
    // also used as increment if initial size found to be insufficient
    static const int maxNnames = 100;

    if (POSIX::debug)
    {
        InfoInFunction
            << "reading directory " << directory << endl;
    }

    // Setup empty string list MAXTVALUES long
    fileNameList dirEntries(maxNnames);

    // Pointers to the directory entries
    DIR *source;
    struct dirent *list;

    // Temporary variables and counters
    label nEntries = 0;

    // Attempt to open directory and set the structure pointer
    if ((source = ::opendir(directory.c_str())) == NULL)
    {
        dirEntries.setSize(0);

        if (POSIX::debug)
        {
            InfoInFunction
                << "cannot open directory " << directory << endl;
        }
    }
    else
    {
        // Read and parse all the entries in the directory
        while ((list = ::readdir(source)) != NULL)
        {
            fileName fName(list->d_name);

            // ignore files beginning with ., i.e. '.', '..' and '.*'
            if (fName.size() && fName[0] != '.')
            {
                const word fExt = fName.ext();

                if
                (
                    (type == fileName::DIRECTORY)
                 ||
                    (
                        type == fileName::FILE
                     && fName[fName.size()-1] != '~'
                     && fExt != "bak"
                     && fExt != "BAK"
                     && fExt != "old"
                     && fExt != "save"
                    )
                )
                {
                    if ((directory/fName).type(followLink) == type)
                    {
                        if (nEntries >= dirEntries.size())
                        {
                            dirEntries.setSize(dirEntries.size() + maxNnames);
                        }

                        if (filtergz && fExt == "gz")
                        {
                            dirEntries[nEntries++] = fName.lessExt();
                        }
                        else
                        {
                            dirEntries[nEntries++] = fName;
                        }
                    }
                }
            }
        }

        // Reset the length of the entries list
        dirEntries.setSize(nEntries);

        ::closedir(source);
    }

    return dirEntries;
}


bool Foam::cp(const fileName& src, const fileName& dest, const bool followLink)
{
    // Make sure source exists.
    if (!exists(src))
    {
        return false;
    }

    fileName destFile(dest);

    // Check type of source file.
    const fileName::Type srcType = src.type(followLink);
    if (srcType == fileName::FILE)
    {
        // If dest is a directory, create the destination file name.
        if (destFile.type() == fileName::DIRECTORY)
        {
            destFile = destFile/src.name();
        }

        // Make sure the destination directory exists.
        if (!isDir(destFile.path()) && !mkDir(destFile.path()))
        {
            return false;
        }

        // Open and check streams.
        std::ifstream srcStream(src.c_str());
        if (!srcStream)
        {
            return false;
        }

        std::ofstream destStream(destFile.c_str());
        if (!destStream)
        {
            return false;
        }

        // Copy character data.
        char ch;
        while (srcStream.get(ch))
        {
            destStream.put(ch);
        }

        // Final check.
        if (!srcStream.eof() || !destStream)
        {
            return false;
        }
    }
    else if (srcType == fileName::LINK)
    {
        // If dest is a directory, create the destination file name.
        if (destFile.type() == fileName::DIRECTORY)
        {
            destFile = destFile/src.name();
        }

        // Make sure the destination directory exists.
        if (!isDir(destFile.path()) && !mkDir(destFile.path()))
        {
            return false;
        }

        ln(src, destFile);
    }
    else if (srcType == fileName::DIRECTORY)
    {
        // If dest is a directory, create the destination file name.
        if (destFile.type() == fileName::DIRECTORY)
        {
            destFile = destFile/src.component(src.components().size() -1);
        }

        // Make sure the destination directory exists.
        if (!isDir(destFile) && !mkDir(destFile))
        {
            return false;
        }

        // Copy files
        fileNameList contents = readDir(src, fileName::FILE, false, followLink);
        forAll(contents, i)
        {
            if (POSIX::debug)
            {
                InfoInFunction
                    << "Copying : " << src/contents[i]
                    << " to " << destFile/contents[i] << endl;
            }

            // File to file.
            cp(src/contents[i], destFile/contents[i], followLink);
        }

        // Copy sub directories.
        fileNameList subdirs = readDir
        (
            src,
            fileName::DIRECTORY,
            false,
            followLink
        );
        forAll(subdirs, i)
        {
            if (POSIX::debug)
            {
                InfoInFunction
                    << "Copying : " << src/subdirs[i]
                    << " to " << destFile << endl;
            }

            // Dir to Dir.
            cp(src/subdirs[i], destFile, followLink);
        }
    }
    else
    {
        return false;
    }

    return true;
}


bool Foam::ln(const fileName& src, const fileName& dst)
{
    if (POSIX::debug)
    {
        InfoInFunction
            << "Create softlink from : " << src << " to " << dst
            << endl;
    }

    if (exists(dst))
    {
        WarningInFunction
            << "destination " << dst << " already exists. Not linking."
            << endl;
        return false;
    }

    if (src.isAbsolute() && !exists(src))
    {
        WarningInFunction
            << "source " << src << " does not exist." << endl;
        return false;
    }

    if (::symlink(src.c_str(), dst.c_str()) == 0)
    {
        return true;
    }
    else
    {
        WarningInFunction
            << "symlink from " << src << " to " << dst << " failed." << endl;
        return false;
    }
}


bool Foam::mv(const fileName& src, const fileName& dst, const bool followLink)
{
    if (POSIX::debug)
    {
        InfoInFunction
            << "Move : " << src << " to " << dst << endl;
    }

    if
    (
        dst.type() == fileName::DIRECTORY
     && src.type(followLink) != fileName::DIRECTORY
    )
    {
        const fileName dstName(dst/src.name());

        return ::rename(src.c_str(), dstName.c_str()) == 0;
    }
    else
    {
        return ::rename(src.c_str(), dst.c_str()) == 0;
    }
}


bool Foam::mvBak(const fileName& src, const std::string& ext)
{
    if (POSIX::debug)
    {
        InfoInFunction
            << "mvBak : " << src << " to extension " << ext << endl;
    }

    if (exists(src, false))
    {
        const int maxIndex = 99;
        char index[3];

        for (int n = 0; n <= maxIndex; n++)
        {
            fileName dstName(src + "." + ext);
            if (n)
            {
                sprintf(index, "%02d", n);
                dstName += index;
            }

            // avoid overwriting existing files, except for the last
            // possible index where we have no choice
            if (!exists(dstName, false) || n == maxIndex)
            {
                return ::rename(src.c_str(), dstName.c_str()) == 0;
            }

        }
    }

    // fall-through: nothing to do
    return false;
}


bool Foam::rm(const fileName& file)
{
    if (POSIX::debug)
    {
        InfoInFunction
            << "Removing : " << file << endl;
    }

    // Try returning plain file name; if not there, try with .gz
    if (remove(file.c_str()) == 0)
    {
        return true;
    }
    else
    {
        return ::remove(string(file + ".gz").c_str()) == 0;
    }
}


bool Foam::rmDir(const fileName& directory)
{
    if (POSIX::debug)
    {
        InfoInFunction
            << "removing directory " << directory << endl;
    }

    // Pointers to the directory entries
    DIR *source;
    struct dirent *list;

    // Attempt to open directory and set the structure pointer
    if ((source = ::opendir(directory.c_str())) == NULL)
    {
        WarningInFunction
            << "cannot open directory " << directory << endl;

        return false;
    }
    else
    {
        // Read and parse all the entries in the directory
        while ((list = ::readdir(source)) != NULL)
        {
            fileName fName(list->d_name);

            if (fName != "." && fName != "..")
            {
                fileName path = directory/fName;

                if (path.type(false) == fileName::DIRECTORY)
                {
                    if (!rmDir(path))
                    {
                        WarningInFunction
                            << "failed to remove directory " << fName
                            << " while removing directory " << directory
                            << endl;

                        ::closedir(source);

                        return false;
                    }
                }
                else
                {
                    if (!rm(path))
                    {
                        WarningInFunction
                            << "failed to remove file " << fName
                            << " while removing directory " << directory
                            << endl;

                        ::closedir(source);

                        return false;
                    }
                }
            }

        }

        if (!rm(directory))
        {
            WarningInFunction
                << "failed to remove directory " << directory << endl;

            ::closedir(source);

            return false;
        }

        ::closedir(source);

        return true;
    }
}


unsigned int Foam::sleep(const unsigned int s)
{
    return ::sleep(s);
}


void Foam::fdClose(const int fd)
{
    if (close(fd) != 0)
    {
        FatalErrorInFunction
            << "close error on " << fd << endl
            << abort(FatalError);
    }
}


bool Foam::ping
(
    const string& destName,
    const label destPort,
    const label timeOut
)
{
    struct hostent *hostPtr;
    volatile int sockfd;
    struct sockaddr_in destAddr;      // will hold the destination addr
    u_int addr;

    if ((hostPtr = ::gethostbyname(destName.c_str())) == NULL)
    {
        FatalErrorInFunction
            << "gethostbyname error " << h_errno << " for host " << destName
            << abort(FatalError);
    }

    // Get first of the SLL of addresses
    addr = (reinterpret_cast<struct in_addr*>(*(hostPtr->h_addr_list)))->s_addr;

    // Allocate socket
    sockfd = ::socket(AF_INET, SOCK_STREAM, 0);
    if (sockfd < 0)
    {
        FatalErrorInFunction
            << "socket error"
            << abort(FatalError);
    }

    // Fill sockaddr_in structure with dest address and port
    memset(reinterpret_cast<char *>(&destAddr), '\0', sizeof(destAddr));
    destAddr.sin_family = AF_INET;
    destAddr.sin_port = htons(ushort(destPort));
    destAddr.sin_addr.s_addr = addr;


    timer myTimer(timeOut);

    if (timedOut(myTimer))
    {
        // Setjmp from timer jumps back to here
        fdClose(sockfd);
        return false;
    }

    if
    (
        ::connect
        (
            sockfd,
            reinterpret_cast<struct sockaddr*>(&destAddr),
            sizeof(struct sockaddr)
        ) != 0
    )
    {
        // Connection refused. Check if network was actually used or not.

        int connectErr = errno;

        fdClose(sockfd);

        if (connectErr == ECONNREFUSED)
        {
            return true;
        }
        //perror("connect");

        return false;
    }

    fdClose(sockfd);

    return true;
}


bool Foam::ping(const string& hostname, const label timeOut)
{
    return ping(hostname, 222, timeOut) || ping(hostname, 22, timeOut);
}


namespace Foam
{
//! \cond fileScope
static int waitpid(const pid_t pid)
{
    // child status, return code from the exec etc.
    int status = 0;

    // in parent - blocking wait
    // modest treatment of signals (in child)
    // treat 'stopped' like exit (suspend/continue)
    while (true)
    {
        pid_t wpid = ::waitpid(pid, &status, WUNTRACED);

        if (wpid == -1)
        {
            FatalErrorInFunction
                << "some error occurred in child"
                << exit(FatalError);
            break;
        }

        if (WIFEXITED(status))
        {
            // child exited, get its return status
            return WEXITSTATUS(status);
        }

        if (WIFSIGNALED(status))
        {
            // child terminated by some signal
            return WTERMSIG(status);
        }

        if (WIFSTOPPED(status))
        {
            // child stopped by some signal
            return WSTOPSIG(status);
        }

        FatalErrorInFunction
            << "programming error, status from waitpid() not handled: "
            << status
            << exit(FatalError);
    }

    return -1;  // should not happen
}
//! \endcond
}


int Foam::system(const std::string& command)
{
    if (command.empty())
    {
        // Treat an empty command as a successful no-op.
        // From 'man sh' POSIX (man sh):
        //   "If the command_string operand is an empty string,
        //    sh shall exit with a zero exit status."
        return 0;
    }

    pid_t child_pid = ::vfork();   // NB: vfork, not fork!
    if (child_pid == -1)
    {
        FatalErrorInFunction
            << "vfork() failed for system command " << command
            << exit(FatalError);
    }

    if (child_pid == 0)
    {
        // in child

        // execl uses the current environ
        (void) ::execl
        (
            "/bin/sh",          // Path of the shell
            "sh",               // Command-name (name for the shell)
            "-c",               // Read commands from the command_string operand.
            command.c_str(),    // Command string
            reinterpret_cast<char *>(0)
        );

        // obviously failed, since exec should not return at all
        FatalErrorInFunction
            << "exec failed: " << command
            << exit(FatalError);
    }


    // in parent - blocking wait
    return waitpid(child_pid);
}


int Foam::system(const Foam::UList<Foam::string>& command)
{
    const int argc = command.size();

    if (!argc)
    {
        // Treat an empty command as a successful no-op.
        // For consistency with POSIX (man sh) behaviour for (sh -c command),
        // which is what is mostly being replicated here.
        return 0;
    }

    // NB: use vfork, not fork!
    // vfork behaves more like a thread and avoids copy-on-write problems
    // triggered by fork.
    // The normal system() command has a fork buried in it that causes
    // issues with infiniband and openmpi etc.
    pid_t child_pid = ::vfork();
    if (child_pid == -1)
    {
        FatalErrorInFunction
            << "vfork() failed for system command " << command[0]
            << exit(FatalError);
    }

    if (child_pid == 0)
    {
        // in child:
        // Need command and arguments separately.
        // args is a NULL-terminated list of c-strings

        CStringList args(SubList<string>(command, 0));
        if (argc > 1)
        {
            args.reset(SubList<string>(command, argc-1, 1));
        }

        // execvp uses the current environ
        (void) ::execvp(command[0].c_str(), args.strings());

        // obviously failed, since exec should not return at all
        FatalErrorInFunction
            << "exec(" << command[0] << ", ...) failed"
            << exit(FatalError);
    }


    // in parent - blocking wait
    return waitpid(child_pid);
}


void* Foam::dlOpen(const fileName& lib, const bool check)
{
    if (POSIX::debug)
    {
        std::cout<< "dlOpen(const fileName&)"
            << " : dlopen of " << lib << std::endl;
    }
    void* handle = ::dlopen(lib.c_str(), RTLD_LAZY|RTLD_GLOBAL);

    if (!handle && check)
    {
        WarningInFunction
            << "dlopen error : " << ::dlerror()
            << endl;
    }

    if (POSIX::debug)
    {
        std::cout
            << "dlOpen(const fileName&)"
            << " : dlopen of " << lib
            << " handle " << handle << std::endl;
    }

    return handle;
}


bool Foam::dlClose(void* handle)
{
    if (POSIX::debug)
    {
        std::cout
            << "dlClose(void*)"
            << " : dlclose of handle " << handle << std::endl;
    }
    return ::dlclose(handle) == 0;
}


void* Foam::dlSym(void* handle, const std::string& symbol)
{
    if (POSIX::debug)
    {
        std::cout
            << "dlSym(void*, const std::string&)"
            << " : dlsym of " << symbol << std::endl;
    }
    // clear any old errors - see manpage dlopen
    (void) ::dlerror();

    // get address of symbol
    void* fun = ::dlsym(handle, symbol.c_str());

    // find error (if any)
    char *error = ::dlerror();

    if (error)
    {
        WarningInFunction
            << "Cannot lookup symbol " << symbol << " : " << error
            << endl;
    }

    return fun;
}


bool Foam::dlSymFound(void* handle, const std::string& symbol)
{
    if (handle && !symbol.empty())
    {
        if (POSIX::debug)
        {
            std::cout
                << "dlSymFound(void*, const std::string&)"
                << " : dlsym of " << symbol << std::endl;
        }

        // clear any old errors - see manpage dlopen
        (void) ::dlerror();

        // get address of symbol
        (void) ::dlsym(handle, symbol.c_str());

        // symbol can be found if there was no error
        return !::dlerror();
    }
    else
    {
        return false;
    }
}


static int collectLibsCallback
(
    struct dl_phdr_info *info,
    size_t size,
    void *data
)
{
    Foam::DynamicList<Foam::fileName>* ptr =
        reinterpret_cast<Foam::DynamicList<Foam::fileName>*>(data);
    ptr->append(info->dlpi_name);
    return 0;
}


Foam::fileNameList Foam::dlLoaded()
{
    DynamicList<fileName> libs;
    dl_iterate_phdr(collectLibsCallback, &libs);
    if (POSIX::debug)
    {
        std::cout
            << "dlLoaded()"
            << " : determined loaded libraries :" << libs.size() << std::endl;
    }
    return libs;
}


void Foam::osRandomSeed(const label seed)
{
    #ifdef USE_RANDOM
    srandom((unsigned int)seed);
    #else
    srand48(seed);
    #endif
}


Foam::label Foam::osRandomInteger()
{
    #ifdef USE_RANDOM
    return random();
    #else
    return lrand48();
    #endif
}


Foam::scalar Foam::osRandomDouble()
{
    #ifdef USE_RANDOM
    return (scalar)random()/INT_MAX;
    #else
    return drand48();
    #endif
}


// ************************************************************************* //