process_spawn.cc

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// Copyright (C) 2015-2024 Internet Systems Consortium, Inc. ("ISC")
//
// This Source Code Form is subject to the terms of the Mozilla Public
// License, v. 2.0. If a copy of the MPL was not distributed with this
// file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
#include <config.h>
 
#include <asiolink/io_service_signal.h>
#include <asiolink/process_spawn.h>
#include <exceptions/exceptions.h>
 
#include <functional>
#include <map>
#include <mutex>
 
#include <cstring>
#include <signal.h>
#include <stdlib.h>
#include <errno.h>
#include <unistd.h>
#include <sys/stat.h>
#include <sys/wait.h>
 
#include <boost/make_shared.hpp>
 
using namespace std;
namespace ph = std::placeholders;
 
extern char **environ;
 
namespace isc {
namespace asiolink {
 
struct ProcessState {
 
    ProcessState() : running_(true), status_(0) {
    }
 
    bool running_;
 
    int status_;
};
 
typedef boost::shared_ptr<ProcessState> ProcessStatePtr;
 
typedef std::map<pid_t, ProcessStatePtr> ProcessStates;
 
class processSpawnImpl;
 
typedef std::map<const ProcessSpawnImpl*, ProcessStates> ProcessCollection;
 
class ProcessSpawnImpl : boost::noncopyable {
public:
 
    ProcessSpawnImpl(const ProcessSpawn::SpawnMode mode,
                     const std::string& executable,
                     const ProcessArgs& args,
                     const ProcessEnvVars& vars,
                     const bool inherit_env);
 
    ~ProcessSpawnImpl();
 
    std::string getCommandLine() const;
 
    pid_t spawn(bool dismiss);
 
    bool isRunning(const pid_t pid) const;
 
    bool isAnyRunning() const;
 
    int getExitStatus(const pid_t pid) const;
 
    void clearState(const pid_t pid);
 
private:
 
    class IOSignalSetInitializer {
    private:
 
        IOSignalSetInitializer(IOServicePtr io_service) {
            if (!io_service) {
                isc_throw(ProcessSpawnError, "NULL IOService instance");
            }
            io_signal_set_ =
                boost::make_shared<IOSignalSet>(io_service,
                                                std::bind(&ProcessSpawnImpl::waitForProcess, ph::_1,
                                                          /* pid = */ -1, /* sync = */ false));
            io_signal_set_->add(SIGCHLD);
        }
 
        ~IOSignalSetInitializer() {
            io_signal_set_->remove(SIGCHLD);
        }
 
    public:
 
        static void initIOSignalSet(IOServicePtr io_service);
 
    private:
 
        IOSignalSetPtr io_signal_set_;
    };
 
    char* allocateInternal(const std::string& src);
 
    static void waitForProcess(int signum, pid_t const wpid = -1,
                               bool const sync = false);
 
    static ProcessCollection process_collection_;
 
    ProcessSpawn::SpawnMode mode_;
 
    std::string executable_;
 
    boost::shared_ptr<char*[]> args_;
 
    boost::shared_ptr<char*[]> vars_;
 
    typedef boost::shared_ptr<char[]> CStringPtr;
 
    std::vector<CStringPtr> storage_;
 
    bool store_;
 
    static std::mutex mutex_;
};
 
ProcessCollection ProcessSpawnImpl::process_collection_;
std::mutex ProcessSpawnImpl::mutex_;
 
void ProcessSpawnImpl::IOSignalSetInitializer::initIOSignalSet(IOServicePtr io_service) {
    static IOSignalSetInitializer init(io_service);
}
 
ProcessSpawnImpl::ProcessSpawnImpl(const ProcessSpawn::SpawnMode mode,
                                   const std::string& executable,
                                   const ProcessArgs& args,
                                   const ProcessEnvVars& vars,
                                   const bool inherit_env)
    : mode_(mode), executable_(executable), args_(new char*[args.size() + 2]),
      store_(false) {
 
    // Size of vars except the trailing null
    size_t vars_size;
    if (inherit_env) {
        size_t i(0);
        while (environ[i]) {
            ++i;
        }
        vars_size = i + vars.size();
    } else {
        vars_size = vars.size();
    }
 
    vars_ = boost::shared_ptr<char*[]>(new char*[vars_size + 1]);
 
    struct stat st;
 
    if (stat(executable_.c_str(), &st)) {
        isc_throw(ProcessSpawnError, "File not found: " << executable_);
    }
 
    if (!(st.st_mode & S_IEXEC)) {
        isc_throw(ProcessSpawnError, "File not executable: " << executable_);
    }
 
    // Conversion of the arguments to the C-style array we start by setting
    // all pointers within an array to NULL to indicate that they haven't
    // been allocated yet.
    memset(args_.get(), 0, (args.size() + 2) * sizeof(char*));
    memset(vars_.get(), 0, (vars_size + 1) * sizeof(char*));
    // By convention, the first argument points to an executable name.
    args_[0] = allocateInternal(executable_);
    // Copy arguments to the array.
    for (size_t i = 1; i <= args.size(); ++i) {
        args_[i] = allocateInternal(args[i - 1]);
    }
    // Copy environment variables to the array.
    size_t i(0);
    if (inherit_env) {
        while (environ[i]) {
            vars_[i] = allocateInternal(environ[i]);
            ++i;
        }
    }
    for (size_t j = 0; j < vars.size(); ++j) {
        vars_[i + j] = allocateInternal(vars[j]);
    }
}
 
ProcessSpawnImpl::~ProcessSpawnImpl() {
    if (store_) {
        lock_guard<std::mutex> lk(mutex_);
        process_collection_.erase(this);
    }
}
 
std::string
ProcessSpawnImpl::getCommandLine() const {
    std::ostringstream s;
    s << executable_;
    // Start with index 1, because the first argument duplicates the
    // path to the executable. Note, that even if there are no parameters
    // the minimum size of the table is 2.
    int i = 1;
    while (args_[i] != NULL) {
        s << " " << args_[i];
        ++i;
    }
    return (s.str());
}
 
pid_t
ProcessSpawnImpl::spawn(bool dismiss) {
    lock_guard<std::mutex> lk(mutex_);
    if (mode_ == ProcessSpawn::ASYNC) {
        ProcessSpawnImpl::IOSignalSetInitializer::initIOSignalSet(ProcessSpawn::getIOService());
    }
    // Create the child
    pid_t pid = fork();
    if (pid < 0) {
        isc_throw(ProcessSpawnError, "unable to fork current process");
 
    } else if (pid == 0) {
        // Reset masked signals for the child process.
        sigset_t sset;
        sigemptyset(&sset);
        pthread_sigmask(SIG_SETMASK, &sset, 0);
        // Run the executable.
        execve(executable_.c_str(), args_.get(), vars_.get());
        // We may end up here if the execve failed, e.g. as a result
        // of issue with permissions or invalid executable name.
        _exit(EXIT_FAILURE);
    }
 
    // We're in the parent process.
    if (!dismiss) {
        store_ = true;
        process_collection_[this].insert(std::pair<pid_t, ProcessStatePtr>(pid, ProcessStatePtr(new ProcessState())));
    }
 
    if (mode_ == ProcessSpawn::SYNC) {
        waitForProcess(SIGCHLD, pid, /* sync = */ true);
    }
 
    return (pid);
}
 
bool
ProcessSpawnImpl::isRunning(const pid_t pid) const {
    lock_guard<std::mutex> lk(mutex_);
    ProcessStates::const_iterator proc;
    if (process_collection_.find(this) == process_collection_.end() ||
        (proc = process_collection_[this].find(pid)) == process_collection_[this].end()) {
        isc_throw(InvalidOperation, "the status of process with pid '" << pid << "' cannot be returned");
    }
    return (proc->second->running_);
}
 
bool
ProcessSpawnImpl::isAnyRunning() const {
    lock_guard<std::mutex> lk(mutex_);
    if (process_collection_.find(this) != process_collection_.end()) {
        for (auto const& proc : process_collection_[this]) {
            if (proc.second->running_) {
                return (true);
            }
        }
    }
    return (false);
}
 
int
ProcessSpawnImpl::getExitStatus(const pid_t pid) const {
    lock_guard<std::mutex> lk(mutex_);
    ProcessStates::const_iterator proc;
    if (process_collection_.find(this) == process_collection_.end() ||
        (proc = process_collection_[this].find(pid)) == process_collection_[this].end()) {
        isc_throw(InvalidOperation, "the status of process with pid '" << pid << "' cannot be returned");
    }
    return (WEXITSTATUS(proc->second->status_));
}
 
char*
ProcessSpawnImpl::allocateInternal(const std::string& src) {
    const size_t src_len = src.length();
    storage_.push_back(CStringPtr(new char[src_len + 1]));
    // Allocate the C-string with one byte more for the null termination.
    char* dest = storage_[storage_.size() - 1].get();
    // copy doesn't append the null at the end.
    src.copy(dest, src_len);
    // Append null on our own.
    dest[src_len] = '\0';
    return (dest);
}
 
void
ProcessSpawnImpl::waitForProcess(int /* signum */,
                                 pid_t const wpid /* = -1 */,
                                 bool sync /* = false */) {
    // In synchronous mode, the lock is taken by the caller function
    // spawn(), so do not deadlock.
    unique_lock<std::mutex> lk{mutex_, std::defer_lock};
    if (!sync) {
        lk.lock();
    }
    for (;;) {
        int status = 0;
        // When called synchronously, this function needs to be blocking.
        // When called asynchronously, the first IO context event is for
        // receiving the SIGCHLD signal which itself is blocking,
        // hence no need to block here too.
        pid_t pid = waitpid(wpid, &status, sync ? 0 : WNOHANG);
        if (pid < 0) {
            if (!sync) {
                break;
            }
            if (errno == EINTR) {
                // On some systems that call sigaction wihout SA_RESTART by default, signals make
                // waitpid exit with EINTR. In this situation, if sync mode is enabled, we're
                // interested in another round of waitpid.
                continue;
            }
            isc_throw(InvalidOperation, "process with pid " << wpid << " has returned " << pid
                                                            << " from waitpid in sync mode, errno: "
                                                            << strerror(errno));
        } else if (pid == 0) {
            if (!sync) {
                break;
            }
        } else /* if (pid > 0) */ {
            for (auto const& instance : process_collection_) {
                auto const& proc = instance.second.find(pid);
                if (proc != instance.second.end()) {
                    proc->second->status_ = status;
                    proc->second->running_ = false;
                }
            }
            if (sync) {
                // Collected process status. Can exit loop.
                break;
            }
        }
    }
}
 
void
ProcessSpawnImpl::clearState(const pid_t pid) {
    if (isRunning(pid)) {
        isc_throw(InvalidOperation, "unable to remove the status for the "
                  "process (pid: " << pid << ") which is still running");
    }
    lock_guard<std::mutex> lk(mutex_);
    if (process_collection_.find(this) != process_collection_.end()) {
        process_collection_[this].erase(pid);
    }
}
 
IOServicePtr ProcessSpawn::io_service_;
 
ProcessSpawn::ProcessSpawn(const SpawnMode mode,
                           const std::string& executable,
                           const ProcessArgs& args,
                           const ProcessEnvVars& vars,
                           const bool inherit_env /* = false */)
    : impl_(new ProcessSpawnImpl(mode, executable, args, vars, inherit_env)) {
}
 
std::string
ProcessSpawn::getCommandLine() const {
    return (impl_->getCommandLine());
}
 
pid_t
ProcessSpawn::spawn(bool dismiss) {
    return (impl_->spawn(dismiss));
}
 
bool
ProcessSpawn::isRunning(const pid_t pid) const {
    return (impl_->isRunning(pid));
}
 
bool
ProcessSpawn::isAnyRunning() const {
    return (impl_->isAnyRunning());
}
 
int
ProcessSpawn::getExitStatus(const pid_t pid) const {
    return (impl_->getExitStatus(pid));
}
 
void
ProcessSpawn::clearState(const pid_t pid) {
    return (impl_->clearState(pid));
}
 
} // namespace asiolink
} // namespace isc