//
// Copyright 2016 Garrett D'Amore <garrett@damore.org>
//
// This software is supplied under the terms of the MIT License, a
// copy of which should be located in the distribution where this
// file was obtained (LICENSE.txt).  A copy of the license may also be
// found online at https://opensource.org/licenses/MIT.
//

#ifndef CORE_PLATFORM_H
#define CORE_PLATFORM_H

// We require some standard C header files.  The only one of these that might
// be problematic is <stdint.h>, which is required for C99.  Older versions
// of the Windows compilers might not have this.  However, latest versions of
// MS Studio have a functional <stdint.h>.  If this impacts you, just upgrade
// your tool chain.
#include <stdarg.h>
#include <stddef.h>
#include <stdint.h>

// These are the APIs that a platform must implement to support nng.

// A word about fork-safety: This library is *NOT* fork safe, in that
// functions may not be called in the child process without an intervening
// exec().  The library attempts to detect this situation, and crashes the
// process with an error message if it encounters it.  (See nn_platform_init
// below.)
//
// Additionally, some file descriptors may leak across fork even to
// child processes.  We make every reasonable effort to ensure that this
// does not occur, but on some platforms there are unavoidable race
// conditions between file creation and marking the file close-on-exec.
//
// Forkers should use posix_spawn() if possible, and as much as possible
// arrange for file close on exec by posix_spawn, or close the descriptors
// they do not need in the child.  (Note that posix_spawn() does *NOT*
// arrange for pthread_atfork() handlers to be called on some platforms.)

// nni_plat_abort crashes the system; it should do whatever is appropriate
// for abnormal programs on the platform, such as calling abort().
extern void nni_plat_abort(void);

// nni_plat_println is used to emit debug messages.  Typically this is used
// during core debugging, or to emit panic messages.  Message content will
// not contain newlines, but the output will add them.
extern void nni_plat_println(const char *);

// nni_alloc allocates memory.  In most cases this can just be malloc().
// However, you may provide a different allocator, for example it is
// possible to use a slab allocator or somesuch.  It is permissible for this
// to return NULL if memory cannot be allocated.
extern void *nni_alloc(size_t);

// nni_free frees memory allocated with nni_alloc. It takes a size because
// some allocators do not track size, or can operate more efficiently if
// the size is provided with the free call.  Examples of this are slab
// allocators like this found in Solaris/illumos (see libumem or kmem).
// This routine does nothing if supplied with a NULL pointer and zero size.
// Most implementations can just call free() here.
extern void nni_free(void *, size_t);

typedef struct nni_mutex	nni_mutex;
typedef struct nni_cond		nni_cond;

typedef struct nni_plat_mtx	nni_plat_mtx;
typedef struct nni_plat_cv	nni_plat_cv;
typedef struct nni_plat_thr	nni_plat_thr;

// Mutex handling.

// nni_mutex_init initializes a mutex structure.  This may require dynamic
// allocation, depending on the platform.  It can return NNG_ENOMEM if that
// fails.
extern int nni_plat_mtx_init(nni_plat_mtx *);
extern int nni_mutex_init(nni_mutex *);

// nni_mutex_fini destroys the mutex and releases any resources allocated for
// it's use.
extern void nni_mutex_fini(nni_mutex *);
extern void nni_plat_mtx_fini(nni_plat_mtx *);

// nni_mutex_enter locks the mutex.  This is not recursive -- a mutex can only
// be entered once.
extern void nni_mutex_enter(nni_mutex *);
extern void nni_plat_mtx_lock(nni_plat_mtx *);

// nni_mutex_exit unlocks the mutex.  This can only be performed by the thread
// that owned the mutex.
extern void nni_mutex_exit(nni_mutex *);
extern void nni_plat_mtx_unlock(nni_plat_mtx *);

// nni_mutex_tryenter tries to lock the mutex.  If it can't, it may return
// NNG_EBUSY.
extern int nni_mutex_tryenter(nni_mutex *);
extern int nni_plat_mtx_trylock(nni_plat_mtx *);

// nni_cond_init initializes a condition variable.  We require a mutex be
// supplied with it, and that mutex must always be held when performing any
// operations on the condition variable (other than fini.)  This may require
// dynamic allocation, and if so this operation may fail with NNG_ENOMEM.
extern int nni_cond_init(nni_cond *, nni_mutex *);
extern int nni_plat_cv_init(nni_plat_cv *, nni_plat_mtx *);

// nni_cond_fini releases all resources associated with condition variable.
extern void nni_cond_fini(nni_cond *);
extern void nni_plat_cv_fini(nni_plat_cv *);

// nni_cond_broadcast wakes all waiters on the condition.  This should be
// called with the lock held.
extern void nni_cond_broadcast(nni_cond *);
extern void nni_plat_cv_wake(nni_plat_cv *);

// nni_cond_signal wakes a signal waiter.
extern void nni_cond_signal(nni_cond *);

// nni_cond_wait waits for a wake up on the condition variable.  The
// associated lock is atomically released and reacquired upon wake up.
// Callers can be spuriously woken.  The associated lock must be held.
extern void nni_cond_wait(nni_cond *);
extern void nni_plat_cv_wait(nni_plat_cv *);

// nni_cond_waituntil waits for a wakeup on the condition variable, or
// until the system time reaches the specified absolute time.  (It is an
// absolute form of nni_cond_timedwait.)  Early wakeups are possible, so
// check the condition.  It will return either NNG_ETIMEDOUT, or 0.
extern int nni_cond_waituntil(nni_cond *, nni_time);
extern int nni_plat_cv_until(nni_plat_cv *, nni_time);

typedef struct nni_thread   nni_thread;

// nni_thread_creates a thread that runs the given function. The thread
// receives a single argument.
extern int nni_thread_create(nni_thread **, void (*fn)(void *), void *);
extern int nni_plat_thr_init(nni_plat_thr *, void (*)(void *), void *);

// nni_thread_reap waits for the thread to exit, and then releases any
// resources associated with the thread.  After this returns, it
// is an error to reference the thread in any further way.
extern void nni_thread_reap(nni_thread *);
extern void nni_plat_thr_fini(nni_plat_thr *);

// nn_clock returns a number of microseconds since some arbitrary time
// in the past.  The values returned by nni_clock must use the same base
// as the times used in nni_cond_waituntil.  The nni_clock() must return
// values > 0, and must return values smaller than 2^63.  (We could relax
// this last constraint, but there is no reason to, and leaves us the option
// of using negative values for other purposes in the future.)
extern nni_time nni_clock(void);

// nni_usleep sleeps for the specified number of microseconds (at least).
extern void nni_usleep(nni_duration);

// nni_plat_init is called to allow the platform the chance to
// do any necessary initialization.  This routine MUST be idempotent,
// and threadsafe, and will be called before any other API calls, and
// may be called at any point thereafter.  It is permitted to return
// an error if some critical failure inializing the platform occurs,
// but once this succeeds, all future calls must succeed as well, unless
// nni_plat_fini has been called.
//
// The function argument should be called if the platform has not initialized
// (i.e. exactly once), and its result passed back to the caller.  If it
// does not return 0 (success), then it may be called again to try to
// initialize the platform again at a later date.
extern int nni_plat_init(int (*)(void));

// nni_plat_fini is called to clean up resources.  It is intended to
// be called as the last thing executed in the library, and no other functions
// will be called until nni_platform_init is called.
extern void nni_plat_fini(void);

// nni_plat_nextid is used to generate a new pipe ID.  This should be an
// increasing value, taken from a random starting point.  (The randomness
// helps ensure we don't confuse pipe IDs from other connections.)  The
// value must be obtained in a threadsafe way (e.g. via an atomic counter
// or under a lock protection.)
extern uint32_t nni_plat_nextid(void);

// Actual platforms we support.  This is included up front so that we can
// get the specific types that are supplied by the platform.
#if defined(PLATFORM_POSIX)
#include "platform/posix/posix_impl.h"
#else
#error "unknown platform"
#endif

#endif // CORE_PLATFORM_H