text: /* yarn.h -- generic interface for thread operations
   * Copyright (C) 2008, 2011, 2012, 2015, 2018 Mark Adler
   * Version 1.5  8 May 2018  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)
  
     -- 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)
   */
  #ifndef _YARN_H
  #define _YARN_H
  #include <stddef.h>
  extern const 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 *, char const *, long);
  #define launch(a, b) launch_(a, b, __FILE__, __LINE__)
  void join_ (thread *, char const *, long);
  #define join(a) join_(a, __FILE__, __LINE__)
  int join_all_ (char const *, long);
  #define join_all() join_all_(__FILE__, __LINE__)
  
  typedef struct lock_s lock;
  lock *new_lock_ (long, char const *, long);
  #define new_lock(a) new_lock_(a, __FILE__, __LINE__)
  void possess_ (lock *, char const *, long);
  #define possess(a) possess_(a, __FILE__, __LINE__)
  void release_ (lock *, char const *, long);
  #define release(a) release_(a, __FILE__, __LINE__)
  enum twist_op
  { TO, BY };
  void twist_ (lock *, enum twist_op, long, char const *, long);
  #define twist(a, b, c) twist_(a, b, c, __FILE__, __LINE__)
  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, char const *, long);
  #define wait_for(a, b, c) wait_for_(a, b, c, __FILE__, __LINE__)
  long peek_lock (lock *);
  void free_lock_ (lock *, char const *, long);
  #define free_lock(a) free_lock_(a, __FILE__, __LINE__)
  #endif
  