/* Thread pool implementation mostly copied from cbs.h */

#include <errno.h>
#include <pthread.h>
#include <stdatomic.h>
#include <stddef.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

#include <alloc.h>
#include <array.h>
#include <errors.h>
#include <macros.h>

#include "globals.h"
#include "tpool.h"
#include "util.h"
#include "work.h"

static int nproc(void);
static void *tpwork(void *);

static pthread_t thread_buffer[32];

int
nproc(void)
{
	int np = getenv_posnum("GRAB_NPROCS", -1);
	if (np != -1)
		return np;
#ifdef _SC_NPROCESSORS_ONLN
	return (int)sysconf(_SC_NPROCESSORS_ONLN);
#else
	return 1;
#endif
}

int
tpinit(tpool_t *tp, const char **files, ptrdiff_t filecnt)
{
	tp->files = files;
	tp->filecnt = filecnt;
	tp->tcnt = nproc();
	tp->tcnt = MIN(tp->tcnt, filecnt);
	tp->wi = 0;

	if (tp->tcnt == 1)
		return 0;               /* Initiate single-threaded behaviour */
	if (tp->tcnt <= 32)
		tp->thrds = thread_buffer;
	else if ((tp->thrds = malloc(sizeof(*tp->thrds) * tp->tcnt)) == nullptr)
		err("malloc:");

	/* If for whatever reason some threads fail to be created, we don’t
       panic but instead just continue using the threads that were able
       to spawn.  If all threads fail to spawn we return 0 and the caller
       will resort to single-threaded behaviour. */

	int n = 0;
	for (int i = 0; i < tp->tcnt; i++) {
		if ((errno = pthread_create(tp->thrds + n, nullptr, tpwork, tp)) != 0)
			warn("failed to create thread:");
		else
			n++;
	}
	return n;
}

void
tpfree(tpool_t *tp)
{
	for (int i = 0; i < tp->tcnt; i++)
		pthread_join(tp->thrds[i], nullptr);

#if DEBUG
	if (tp->thrds != thread_buffer)
		free(tp->thrds);
#endif
}

void *
tpwork(void *arg)
{
	tpool_t *tp = arg;

	allocator_t mem = init_heap_allocator(nullptr);
	unsigned char *buf = array_new(mem, typeof(*buf), 4096);

	for (;;) {
		ptrdiff_t i = atomic_fetch_add(&tp->wi, 1);
		if (i >= tp->filecnt)
			break;
		process_file(tp->files[i], &buf);
	}

	fwrite(buf, 1, array_len(buf), stdout);

#if DEBUG
	array_free(buf);
#endif
	return nullptr;
}