diff --git a/pigz/yarn.c b/pigz/yarn.c
new file mode 100644
index 0000000..0562e70
--- /dev/null
+++ b/pigz/yarn.c
@@ -0,0 +1,365 @@
+/* yarn.c -- generic thread operations implemented using pthread functions
+ * Copyright (C) 2008 Mark Adler
+ * Version 1.1  26 Oct 2008  Mark Adler
+ * For conditions of distribution and use, see copyright notice in yarn.h
+ */
+
+/* Basic thread operations implemented using the POSIX pthread library.  All
+   pthread references are isolated within this module to allow alternate
+   implementations with other thread libraries.  See yarn.h for the description
+   of these operations. */
+
+/* Version history:
+   1.0    19 Oct 2008  First version
+   1.1    26 Oct 2008  No need to set the stack size -- remove
+                       Add yarn_abort() function for clean-up on error exit
+ */
+
+/* for thread portability */
+#define _POSIX_PTHREAD_SEMANTICS
+#define _REENTRANT
+
+/* external libraries and entities referenced */
+#include <stdio.h>      /* fprintf(), stderr */
+#include <stdlib.h>     /* exit(), malloc(), free(), NULL */
+#include <pthread.h>    /* pthread_t, pthread_create(), pthread_join(), */
+    /* pthread_attr_t, pthread_attr_init(), pthread_attr_destroy(),
+       PTHREAD_CREATE_JOINABLE, pthread_attr_setdetachstate(),
+       pthread_self(), pthread_equal(),
+       pthread_mutex_t, PTHREAD_MUTEX_INITIALIZER, pthread_mutex_init(),
+       pthread_mutex_lock(), pthread_mutex_unlock(), pthread_mutex_destroy(),
+       pthread_cond_t, PTHREAD_COND_INITIALIZER, pthread_cond_init(),
+       pthread_cond_broadcast(), pthread_cond_wait(), pthread_cond_destroy() */
+#include <errno.h>      /* ENOMEM, EAGAIN, EINVAL */
+
+/* interface definition */
+#include "yarn.h"
+
+/* constants */
+#define local static            /* for non-exported functions and globals */
+
+/* error handling external globals, resettable by application */
+char *yarn_prefix = "yarn";
+void (*yarn_abort)(int) = NULL;
+
+
+/* immediately exit -- use for errors that shouldn't ever happen */
+local void fail(int err)
+{
+    fprintf(stderr, "%s: %s (%d) -- aborting\n", yarn_prefix,
+            err == ENOMEM ? "out of memory" : "internal pthread error", err);
+    if (yarn_abort != NULL)
+        yarn_abort(err);
+    exit(err == ENOMEM || err == EAGAIN ? err : EINVAL);
+}
+
+/* memory handling routines provided by user -- if none are provided, malloc()
+   and free() are used, which are therefore assumed to be thread-safe */
+typedef void *(*malloc_t)(size_t);
+typedef void (*free_t)(void *);
+local malloc_t my_malloc_f = malloc;
+local free_t my_free = free;
+
+/* use user-supplied allocation routines instead of malloc() and free() */
+void yarn_mem(malloc_t lease, free_t vacate)
+{
+    my_malloc_f = lease;
+    my_free = vacate;
+}
+
+/* memory allocation that cannot fail (from the point of view of the caller) */
+local void *my_malloc(size_t size)
+{
+    void *block;
+
+    if ((block = my_malloc_f(size)) == NULL)
+        fail(ENOMEM);
+    return block;
+}
+
+/* -- lock functions -- */
+
+struct lock_s {
+    pthread_mutex_t mutex;
+    pthread_cond_t cond;
+    long value;
+};
+
+lock *new_lock(long initial)
+{
+    int ret;
+    lock *bolt;
+
+    bolt = my_malloc(sizeof(struct lock_s));
+    if ((ret = pthread_mutex_init(&(bolt->mutex), NULL)) ||
+        (ret = pthread_cond_init(&(bolt->cond), NULL)))
+        fail(ret);
+    bolt->value = initial;
+    return bolt;
+}
+
+void possess(lock *bolt)
+{
+    int ret;
+
+    if ((ret = pthread_mutex_lock(&(bolt->mutex))) != 0)
+        fail(ret);
+}
+
+void release(lock *bolt)
+{
+    int ret;
+
+    if ((ret = pthread_mutex_unlock(&(bolt->mutex))) != 0)
+        fail(ret);
+}
+
+void twist(lock *bolt, enum twist_op op, long val)
+{
+    int ret;
+
+    if (op == TO)
+        bolt->value = val;
+    else if (op == BY)
+        bolt->value += val;
+    if ((ret = pthread_cond_broadcast(&(bolt->cond))) ||
+        (ret = pthread_mutex_unlock(&(bolt->mutex))))
+        fail(ret);
+}
+
+#define until(a) while(!(a))
+
+void wait_for(lock *bolt, enum wait_op op, long val)
+{
+    int ret;
+
+    switch (op) {
+    case TO_BE:
+        until (bolt->value == val)
+            if ((ret = pthread_cond_wait(&(bolt->cond), &(bolt->mutex))) != 0)
+                fail(ret);
+        break;
+    case NOT_TO_BE:
+        until (bolt->value != val)
+            if ((ret = pthread_cond_wait(&(bolt->cond), &(bolt->mutex))) != 0)
+                fail(ret);
+        break;
+    case TO_BE_MORE_THAN:
+        until (bolt->value > val)
+            if ((ret = pthread_cond_wait(&(bolt->cond), &(bolt->mutex))) != 0)
+                fail(ret);
+        break;
+    case TO_BE_LESS_THAN:
+        until (bolt->value < val)
+            if ((ret = pthread_cond_wait(&(bolt->cond), &(bolt->mutex))) != 0)
+                fail(ret);
+    }
+}
+
+long peek_lock(lock *bolt)
+{
+    return bolt->value;
+}
+
+void free_lock(lock *bolt)
+{
+    int ret;
+    if ((ret = pthread_cond_destroy(&(bolt->cond))) ||
+        (ret = pthread_mutex_destroy(&(bolt->mutex))))
+        fail(ret);
+    my_free(bolt);
+}
+
+/* -- thread functions (uses lock functions above) -- */
+
+struct thread_s {
+    pthread_t id;
+    int done;                   /* true if this thread has exited */
+    thread *next;               /* for list of all launched threads */
+};
+
+/* list of threads launched but not joined, count of threads exited but not
+   joined (incremented by ignition() just before exiting) */
+local lock threads_lock = {
+    PTHREAD_MUTEX_INITIALIZER,
+    PTHREAD_COND_INITIALIZER,
+    0                           /* number of threads exited but not joined */
+};
+local thread *threads = NULL;       /* list of extant threads */
+
+/* structure in which to pass the probe and its payload to ignition() */
+struct capsule {
+    void (*probe)(void *);
+    void *payload;
+};
+
+/* mark the calling thread as done and alert join_all() */
+local void reenter(void *dummy)
+{
+    thread *match, **prior;
+    pthread_t me;
+
+    /* find this thread in the threads list by matching the thread id */
+    me = pthread_self();
+    possess(&(threads_lock));
+    prior = &(threads);
+    while ((match = *prior) != NULL) {
+        if (pthread_equal(match->id, me))
+            break;
+        prior = &(match->next);
+    }
+    if (match == NULL)
+        fail(EINVAL);
+
+    /* mark this thread as done and move it to the head of the list */
+    match->done = 1;
+    if (threads != match) {
+        *prior = match->next;
+        match->next = threads;
+        threads = match;
+    }
+
+    /* update the count of threads to be joined and alert join_all() */
+    twist(&(threads_lock), BY, +1);
+}
+
+/* all threads go through this routine so that just before the thread exits,
+   it marks itself as done in the threads list and alerts join_all() so that
+   the thread resources can be released -- use cleanup stack so that the
+   marking occurs even if the thread is cancelled */
+local void *ignition(void *arg)
+{
+    struct capsule *capsule = arg;
+
+    /* run reenter() before leaving */
+    pthread_cleanup_push(reenter, NULL);
+
+    /* execute the requested function with argument */
+    capsule->probe(capsule->payload);
+    my_free(capsule);
+
+    /* mark this thread as done and let join_all() know */
+    pthread_cleanup_pop(1);
+
+    /* exit thread */
+    return NULL;
+}
+
+/* not all POSIX implementations create threads as joinable by default, so that
+   is made explicit here */
+thread *launch(void (*probe)(void *), void *payload)
+{
+    int ret;
+    thread *th;
+    struct capsule *capsule;
+    pthread_attr_t attr;
+
+    /* construct the requested call and argument for the ignition() routine
+       (allocated instead of automatic so that we're sure this will still be
+       there when ignition() actually starts up -- ignition() will free this
+       allocation) */
+    capsule = my_malloc(sizeof(struct capsule));
+    capsule->probe = probe;
+    capsule->payload = payload;
+
+    /* assure this thread is in the list before join_all() or ignition() looks
+       for it */
+    possess(&(threads_lock));
+
+    /* create the thread and call ignition() from that thread */
+    th = my_malloc(sizeof(struct thread_s));
+    if ((ret = pthread_attr_init(&attr)) ||
+        (ret = pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_JOINABLE)) ||
+        (ret = pthread_create(&(th->id), &attr, ignition, capsule)) ||
+        (ret = pthread_attr_destroy(&attr)))
+        fail(ret);
+
+    /* put the thread in the threads list for join_all() */
+    th->done = 0;
+    th->next = threads;
+    threads = th;
+    release(&(threads_lock));
+    return th;
+}
+
+void join(thread *ally)
+{
+    int ret;
+    thread *match, **prior;
+
+    /* wait for thread to exit and return its resources */
+    if ((ret = pthread_join(ally->id, NULL)) != 0)
+        fail(ret);
+
+    /* find the thread in the threads list */
+    possess(&(threads_lock));
+    prior = &(threads);
+    while ((match = *prior) != NULL) {
+        if (match == ally)
+            break;
+        prior = &(match->next);
+    }
+    if (match == NULL)
+        fail(EINVAL);
+
+    /* remove thread from list and update exited count, free thread */
+    if (match->done)
+        threads_lock.value--;
+    *prior = match->next;
+    release(&(threads_lock));
+    my_free(ally);
+}
+
+/* This implementation of join_all() only attempts to join threads that have
+   announced that they have exited (see ignition()).  When there are many
+   threads, this is faster than waiting for some random thread to exit while a
+   bunch of other threads have already exited. */
+int join_all(void)
+{
+    int ret, count;
+    thread *match, **prior;
+
+    /* grab the threads list and initialize the joined count */
+    count = 0;
+    possess(&(threads_lock));
+
+    /* do until threads list is empty */
+    while (threads != NULL) {
+        /* wait until at least one thread has reentered */
+        wait_for(&(threads_lock), NOT_TO_BE, 0);
+
+        /* find the first thread marked done (should be at or near the top) */
+        prior = &(threads);
+        while ((match = *prior) != NULL) {
+            if (match->done)
+                break;
+            prior = &(match->next);
+        }
+        if (match == NULL)
+            fail(EINVAL);
+
+        /* join the thread (will be almost immediate), remove from the threads
+           list, update the reenter count, and free the thread */
+        if ((ret = pthread_join(match->id, NULL)) != 0)
+            fail(ret);
+        threads_lock.value--;
+        *prior = match->next;
+        my_free(match);
+        count++;
+    }
+
+    /* let go of the threads list and return the number of threads joined */
+    release(&(threads_lock));
+    return count;
+}
+
+/* cancel and join the thread -- the thread will cancel when it gets to a file
+   operation, a sleep or pause, or a condition wait */
+void destruct(thread *off_course)
+{
+    int ret;
+
+    if ((ret = pthread_cancel(off_course->id)) != 0)
+        fail(ret);
+    join(off_course);
+}