/* yarn.h -- generic interface for thread operations
* Copyright (C) 2008, 2011 Mark Adler
* Version 1.3  13 Jan 2012  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
 [email protected]
*/

/* 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_prefix - 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 *);

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