TokenServer & copyClosureTokenServer, counter & bytesSent,

    counter & bytesSent,

    /* Ensure that only a limited number of threads can copy closures
       at the same time. However, proceed anyway after a timeout to
       prevent starvation by a handful of really huge closures. */
    time_t start = time(0);
    int timeout = 60 * (10 + rand() % 5);
    auto token(copyClosureTokenServer.get(timeout));
    time_t stop = time(0);

    if (token())
        printMsg(lvlDebug, format("got copy closure token after %1%s") % (stop - start));
    else
        printMsg(lvlDebug, format("did not get copy closure token after %1%s") % (stop - start));

        copyClosureTo(store, from, to, inputs, copyClosureTokenServer, bytesSent);

        std::lock_guard<std::mutex> sendLock(machine->state->sendLock);
        copyClosureTo(store, from, to, inputs, bytesSent);

    : copyClosureTokenServer{maxParallelCopyClosure}

#include "token-server.hh"

        /* Mutex to prevent multiple threads from sending data to the
           same machine (which would be inefficient). */
        std::mutex sendLock;

    /* Token server limiting the number of threads copying closures in
       parallel to prevent excessive I/O load. */
    TokenServer copyClosureTokenServer;