fish-shell/iothread.cpp

#include "config.h"
#include "iothread.h"
#include "common.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>
#include <fcntl.h>
#include <queue>

#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 {
	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 std::queue<ThreadedRequest_t *> s_request_queue;
static int s_last_sequence_number;
static int s_read_pipe, s_write_pipe;

static void iothread_init(void) {
	static bool inited = false;
	if (! inited) {
		inited = true;
		
		/* 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];
        
        // 0 means success to VOMIT_ON_FAILURE. Arrange to pass 0 if fcntl returns anything other than -1.
        VOMIT_ON_FAILURE(-1 == fcntl(s_read_pipe, F_SETFD, FD_CLOEXEC));
        VOMIT_ON_FAILURE(-1 == fcntl(s_write_pipe, F_SETFD, FD_CLOEXEC));
		
		/* 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) {
	ASSERT_IS_LOCKED(s_request_queue_lock);
    s_request_queue.push(req);
}

static ThreadedRequest_t *dequeue_request(void) {
    ThreadedRequest_t *result = NULL;
    scoped_lock lock(s_request_queue_lock);
    if (! s_request_queue.empty()) {
        result = s_request_queue.front();
        s_request_queue.pop();
    }
    return result;
}

/* 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 = dequeue_request();

	/* 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_loop(s_write_pipe, (const char *)&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) {
    ASSERT_IS_LOCKED(s_request_queue_lock);
	if (! s_request_queue.empty() && 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_base(int (*handler)(void *), void (*completionCallback)(void *, int), void *context) {
    ASSERT_IS_MAIN_THREAD();
    ASSERT_IS_NOT_FORKED_CHILD();
	iothread_init();
	
	/* Create and initialize a request. */
	struct ThreadedRequest_t *req = new ThreadedRequest_t();
	req->handler = handler;
	req->completionCallback = completionCallback;
	req->context = context;
	req->sequenceNumber = ++s_last_sequence_number;

    /* Take our lock */
    scoped_lock lock(s_request_queue_lock);
    
    /* Add to the queue */
    add_to_queue(req);
    
    /* Spawn a thread if necessary */
    iothread_spawn_if_needed();
    return 0;
}

int iothread_port(void) {
	iothread_init();
	return s_read_pipe;
}

void iothread_service_completion(void) {
    ASSERT_IS_MAIN_THREAD();
	ThreadIndex_t threadIdx = (ThreadIndex_t)-1;
	VOMIT_ON_FAILURE(1 != read_loop(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) {
        if (req->completionCallback) 
            req->completionCallback(req->context, req->handlerResult);
        delete req;
    }
    
	/* 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));
}

void iothread_drain_all(void) {
    ASSERT_IS_MAIN_THREAD();
    ASSERT_IS_NOT_FORKED_CHILD();
    while (s_active_thread_count > 0) {
        iothread_service_completion();
    }
}