/*
 *
 * Copyright 2015 gRPC authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 *
 */

/*
 * wakeup_fd abstracts the concept of a file descriptor for the purpose of
 * waking up a thread in select()/poll()/epoll_wait()/etc.

 * The poll() family of system calls provide a way for a thread to block until
 * there is activity on one (or more) of a set of file descriptors. An
 * application may wish to wake up this thread to do non file related work. The
 * typical way to do this is to add a pipe to the set of file descriptors, then
 * write to the pipe to wake up the thread in poll().
 *
 * Linux has a lighter weight eventfd specifically designed for this purpose.
 * wakeup_fd abstracts the difference between the two.
 *
 * Setup:
 * 1. Before calling anything, call global_init() at least once.
 * 1. Call grpc_wakeup_fd_init() to set up a wakeup_fd.
 * 2. Add the result of GRPC_WAKEUP_FD_FD to the set of monitored file
 *    descriptors for the poll() style API you are using. Monitor the file
 *    descriptor for readability.
 * 3. To tear down, call grpc_wakeup_fd_destroy(). This closes the underlying
 *    file descriptor.
 *
 * Usage:
 * 1. To wake up a polling thread, call grpc_wakeup_fd_wakeup() on a wakeup_fd
 *    it is monitoring.
 * 2. If the polling thread was awakened by a wakeup_fd event, call
 *    grpc_wakeup_fd_consume_wakeup() on it.
 */
#ifndef GRPC_CORE_LIB_IOMGR_WAKEUP_FD_POSIX_H
#define GRPC_CORE_LIB_IOMGR_WAKEUP_FD_POSIX_H

#include "src/core/lib/iomgr/error.h"

void grpc_wakeup_fd_global_init(void);
void grpc_wakeup_fd_global_destroy(void);

/* Force using the fallback implementation. This is intended for testing
 * purposes only.*/
void grpc_wakeup_fd_global_init_force_fallback(void);

int grpc_has_wakeup_fd(void);
int grpc_cv_wakeup_fds_enabled(void);
void grpc_enable_cv_wakeup_fds(int enable);

typedef struct grpc_wakeup_fd grpc_wakeup_fd;

typedef struct grpc_wakeup_fd_vtable {
  grpc_error* (*init)(grpc_wakeup_fd* fd_info);
  grpc_error* (*consume)(grpc_wakeup_fd* fd_info);
  grpc_error* (*wakeup)(grpc_wakeup_fd* fd_info);
  void (*destroy)(grpc_wakeup_fd* fd_info);
  /* Must be called before calling any other functions */
  int (*check_availability)(void);
} grpc_wakeup_fd_vtable;

struct grpc_wakeup_fd {
  int read_fd;
  int write_fd;
};

extern int grpc_allow_specialized_wakeup_fd;
extern int grpc_allow_pipe_wakeup_fd;

#define GRPC_WAKEUP_FD_GET_READ_FD(fd_info) ((fd_info)->read_fd)

grpc_error* grpc_wakeup_fd_init(grpc_wakeup_fd* fd_info) GRPC_MUST_USE_RESULT;
grpc_error* grpc_wakeup_fd_consume_wakeup(grpc_wakeup_fd* fd_info)
    GRPC_MUST_USE_RESULT;
grpc_error* grpc_wakeup_fd_wakeup(grpc_wakeup_fd* fd_info) GRPC_MUST_USE_RESULT;
void grpc_wakeup_fd_destroy(grpc_wakeup_fd* fd_info);

/* Defined in some specialized implementation's .c file, or by
 * wakeup_fd_nospecial.c if no such implementation exists. */
extern const grpc_wakeup_fd_vtable grpc_specialized_wakeup_fd_vtable;

#endif /* GRPC_CORE_LIB_IOMGR_WAKEUP_FD_POSIX_H */
