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#include "iothread.h"
#include <pthread.h>
#include <assert.h>
#include <errno.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <unistd.h>
#include <signal.h>
#define VOMIT_ON_FAILURE(a) do { if (0 != (a)) { int err = errno; fprintf(stderr, "%s failed on line %d in file %s: %d (%s)\n", #a, __LINE__, __FILE__, err, strerror(err)); abort(); }} while (0)
#ifdef _POSIX_THREAD_THREADS_MAX
#if _POSIX_THREAD_THREADS_MAX < 64
#define IO_MAX_THREADS _POSIX_THREAD_THREADS_MAX
#endif
#endif
#ifndef IO_MAX_THREADS
#define IO_MAX_THREADS 64
#endif
static int s_active_thread_count;
typedef unsigned char ThreadIndex_t;
static struct WorkerThread_t {
ThreadIndex_t idx;
pthread_t thread;
} threads[IO_MAX_THREADS];
struct ThreadedRequest_t {
struct ThreadedRequest_t *next;
int sequenceNumber;
int (*handler)(void *);
void (*completionCallback)(void *, int);
void *context;
int handlerResult;
};
static struct WorkerThread_t *next_vacant_thread_slot(void) {
for (ThreadIndex_t i=0; i < IO_MAX_THREADS; i++) {
if (! threads[i].thread) return &threads[i];
}
return NULL;
}
static pthread_mutex_t s_request_queue_lock;
static struct ThreadedRequest_t *s_request_queue_head;
static int s_last_sequence_number;
static int s_read_pipe, s_write_pipe;
static void iothread_init(void) {
static int inited = 0;
if (! inited) {
inited = 1;
/* Initialize the queue lock */
VOMIT_ON_FAILURE(pthread_mutex_init(&s_request_queue_lock, NULL));
/* Initialize the completion pipes */
int pipes[2] = {0, 0};
VOMIT_ON_FAILURE(pipe(pipes));
s_read_pipe = pipes[0];
s_write_pipe = pipes[1];
/* Tell each thread its index */
for (ThreadIndex_t i=0; i < IO_MAX_THREADS; i++) {
threads[i].idx = i;
}
}
}
static void add_to_queue(struct ThreadedRequest_t *req) {
//requires that the queue lock be held
if (s_request_queue_head == NULL) {
s_request_queue_head = req;
} else {
struct ThreadedRequest_t *last_in_queue = s_request_queue_head;
while (last_in_queue->next != NULL) {
last_in_queue = last_in_queue->next;
}
last_in_queue->next = req;
}
}
/* The function that does thread work. */
static void *iothread_worker(void *threadPtr) {
assert(threadPtr != NULL);
struct WorkerThread_t *thread = (struct WorkerThread_t *)threadPtr;
// We don't want to receive signals on this thread
sigset_t set;
sigfillset(&set);
VOMIT_ON_FAILURE(pthread_sigmask(SIG_SETMASK, &set, NULL));
/* Grab a request off of the queue */
struct ThreadedRequest_t *req;
VOMIT_ON_FAILURE(pthread_mutex_lock(&s_request_queue_lock));
req = s_request_queue_head;
if (req) {
s_request_queue_head = req->next;
}
VOMIT_ON_FAILURE(pthread_mutex_unlock(&s_request_queue_lock));
/* Run the handler and store the result */
if (req) {
req->handlerResult = req->handler(req->context);
}
/* Write our index to wake up the main thread */
VOMIT_ON_FAILURE(! write(s_write_pipe, &thread->idx, sizeof thread->idx));
/* We're done */
return req;
}
/* Spawn another thread if there's work to be done. */
static void iothread_spawn_if_needed(void) {
if (s_request_queue_head != NULL && s_active_thread_count < IO_MAX_THREADS) {
struct WorkerThread_t *thread = next_vacant_thread_slot();
assert(thread != NULL);
/* Spawn a thread */
int err;
do {
err = 0;
if (pthread_create(&thread->thread, NULL, iothread_worker, thread)) {
err = errno;
}
} while (err == EAGAIN);
assert(err == 0);
/* Note that we are spawned another thread */
s_active_thread_count += 1;
}
}
int iothread_perform(int (*handler)(void *), void (*completionCallback)(void *, int), void *context) {
iothread_init();
/* Create and initialize a request. */
struct ThreadedRequest_t *req = (struct ThreadedRequest_t *)malloc(sizeof *req);
req->next = NULL;
req->handler = handler;
req->completionCallback = completionCallback;
req->context = context;
req->sequenceNumber = ++s_last_sequence_number;
/* Take the queue lock */
VOMIT_ON_FAILURE(pthread_mutex_lock(&s_request_queue_lock));
/* Add to the queue */
add_to_queue(req);
/* Spawn a thread if necessary */
iothread_spawn_if_needed();
/* Unlock */
VOMIT_ON_FAILURE(pthread_mutex_unlock(&s_request_queue_lock));
return 0;
}
int iothread_port(void) {
iothread_init();
return s_read_pipe;
}
void iothread_service_completion(void) {
ThreadIndex_t threadIdx = (ThreadIndex_t)-1;
VOMIT_ON_FAILURE(! read(iothread_port(), &threadIdx, sizeof threadIdx));
assert(threadIdx < IO_MAX_THREADS);
struct WorkerThread_t *thread = &threads[threadIdx];
assert(thread->thread != 0);
struct ThreadedRequest_t *req = NULL;
VOMIT_ON_FAILURE(pthread_join(thread->thread, (void **)&req));
/* Free up this thread */
thread->thread = 0;
assert(s_active_thread_count > 0);
s_active_thread_count -= 1;
/* Handle the request */
if (req && req->completionCallback) {
req->completionCallback(req->context, req->handlerResult);
}
/* Maybe spawn another thread, if there's more work to be done. */
VOMIT_ON_FAILURE(pthread_mutex_lock(&s_request_queue_lock));
iothread_spawn_if_needed();
VOMIT_ON_FAILURE(pthread_mutex_unlock(&s_request_queue_lock));
}
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