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+/* yarn.h -- generic interface for thread operations
+ * Copyright (C) 2008 Mark Adler
+ * Version 1.1  26 Oct 2008  Mark Adler
+ */
+
+/*
+  This software is provided 'as-is', without any express or implied
+  warranty.  In no event will the author be held liable for any damages
+  arising from the use of this software.
+
+  Permission is granted to anyone to use this software for any purpose,
+  including commercial applications, and to alter it and redistribute it
+  freely, subject to the following restrictions:
+
+  1. The origin of this software must not be misrepresented; you must not
+     claim that you wrote the original software. If you use this software
+     in a product, an acknowledgment in the product documentation would be
+     appreciated but is not required.
+  2. Altered source versions must be plainly marked as such, and must not be
+     misrepresented as being the original software.
+  3. This notice may not be removed or altered from any source distribution.
+
+  Mark Adler
+  madler@alumni.caltech.edu
+ */
+
+/* Basic thread operations
+
+   This interface isolates the local operating system implementation of threads
+   from the application in order to facilitate platform independent use of
+   threads.  All of the implementation details are deliberately hidden.
+
+   Assuming adequate system resources and proper use, none of these functions
+   can fail.  As a result, any errors encountered will cause an exit() to be
+   executed.
+
+   These functions allow the simple launching and joining of threads, and the
+   locking of objects and synchronization of changes of objects.  The latter is
+   implemented with a single lock type that contains an integer value.  The
+   value can be ignored for simple exclusive access to an object, or the value
+   can be used to signal and wait for changes to an object.
+
+   -- Arguments --
+
+   thread *thread;          identifier for launched thread, used by join
+   void probe(void *);      pointer to function "probe", run when thread starts
+   void *payload;           single argument passed to the probe function
+   lock *lock;              a lock with a value -- used for exclusive access to
+                            an object and to synchronize threads waiting for
+                            changes to an object
+   long val;                value to set lock, increment lock, or wait for
+   int n;                   number of threads joined
+
+   -- Thread functions --
+
+   thread = launch(probe, payload) - launch a thread -- exit via probe() return
+   join(thread) - join a thread and by joining end it, waiting for the thread
+        to exit if it hasn't already -- will free the resources allocated by
+        launch() (don't try to join the same thread more than once)
+   n = join_all() - join all threads launched by launch() that are not joined
+        yet and free the resources allocated by the launches, usually to clean
+        up when the thread processing is done -- join_all() returns an int with
+        the count of the number of threads joined (join_all() should only be
+        called from the main thread, and should only be called after any calls
+        of join() have completed)
+   destruct(thread) - terminate the thread in mid-execution and join it
+        (depending on the implementation, the termination may not be immediate,
+        but may wait for the thread to execute certain thread or file i/o
+        operations)
+
+   -- Lock functions --
+
+   lock = new_lock(val) - create a new lock with initial value val (lock is
+        created in the released state)
+   possess(lock) - acquire exclusive possession of a lock, waiting if necessary
+   twist(lock, [TO | BY], val) - set lock to or increment lock by val, signal
+        all threads waiting on this lock and then release the lock -- must
+        possess the lock before calling (twist releases, so don't do a
+        release() after a twist() on the same lock)
+   wait_for(lock, [TO_BE | NOT_TO_BE | TO_BE_MORE_THAN | TO_BE_LESS_THAN], val)
+        - wait on lock value to be, not to be, be greater than, or be less than
+        val -- must possess the lock before calling, will possess the lock on
+        return but the lock is released while waiting to permit other threads
+        to use twist() to change the value and signal the change (so make sure
+        that the object is in a usable state when waiting)
+   release(lock) - release a possessed lock (do not try to release a lock that
+        the current thread does not possess)
+   val = peek_lock(lock) - return the value of the lock (assumes that lock is
+        already possessed, no possess or release is done by peek_lock())
+   free_lock(lock) - free the resources allocated by new_lock() (application
+        must assure that the lock is released before calling free_lock())
+
+   -- Memory allocation ---
+
+   yarn_mem(better_malloc, better_free) - set the memory allocation and free
+        routines for use by the yarn routines where the supplied routines have
+        the same interface and operation as malloc() and free(), and may be
+        provided in order to supply thread-safe memory allocation routines or
+        for any other reason -- by default malloc() and free() will be used
+
+   -- Error control --
+
+   yarn_name - a char pointer to a string that will be the prefix for any error
+        messages that these routines generate before exiting -- if not changed
+        by the application, "yarn" will be used
+   yarn_abort - an external function that will be executed when there is an
+        internal yarn error, due to out of memory or misuse -- this function
+        may exit to abort the application, or if it returns, the yarn error
+        handler will exit (set to NULL by default for no action)
+ */
+
+extern char *yarn_prefix;
+extern void (*yarn_abort)(int);
+
+void yarn_mem(void *(*)(size_t), void (*)(void *));
+
+typedef struct thread_s thread;
+thread *launch(void (*)(void *), void *);
+void join(thread *);
+int join_all(void);
+void destruct(thread *);
+
+typedef struct lock_s lock;
+lock *new_lock(long);
+void possess(lock *);
+void release(lock *);
+enum twist_op { TO, BY };
+void twist(lock *, enum twist_op, long);
+enum wait_op {
+    TO_BE, /* or */ NOT_TO_BE, /* that is the question */
+    TO_BE_MORE_THAN, TO_BE_LESS_THAN };
+void wait_for(lock *, enum wait_op, long);
+long peek_lock(lock *);
+void free_lock(lock *);