Android RIL源码研究笔记 の ril_event

Android源码目录hardware/ril/libril目录中总共包含5个C/CPP文件，它们分别是ril_commands.h、ril_unsol_commands.h、ril_event.h、ril_event.cpp和ril.cpp。这篇文章主要分析ril_event的相关代码。

ril_event主要处理电话模块涉及的端口、modem等产生的事件，并将多个事件按时间顺序进行组织，并保存在事件队别中，主要使用了三个队列，分别是：watch_table[]，timer_list和pending_list。代码是以C语言方式实现的，先来看头文件ril_event.h：

// 每次监视的最大的文件描述符句柄数，可以根据需要自行修改
#define MAX_FD_EVENTS 8

// ril_event的回调函数
typedef void (*ril_event_cb)(int fd, short events, void *userdata);

struct ril_event {
	// 用于将ril_event串成双向链表的前向指针和后向指针
    struct ril_event *next;
	struct ril_event *prev;
	
	//ril事件相关的文件描述符句柄（可以是文件、管道、Socket等）
	int fd;
	
	//这个事件在监控列表中的索引
	int index;
	
	//当一个事件处理完后（即从watch_table移到pending_list中等待处理），
	//persist参数决定这个事件是否一直存在于监控列表watch_table[]中
	bool persist;
	
	//事件的超时时间
	struct timeval timeout;
	
	//回调函数及其传入的参数
    ril_event_cb func;
    void *param;
};

//以下是ril事件相关的一些操作函数
// 初始化内部数据结构
void ril_event_init();

// 初始化一个ril事件
void ril_event_set(struct ril_event * ev, int fd, bool persist, ril_event_cb func, void * param);

// 将事件添加到监控列表watch_table[]中
void ril_event_add(struct ril_event * ev);

// 增加一个timer事件到timer_list链表中
void ril_timer_add(struct ril_event * ev, struct timeval * tv);

// 将指定的事件从监控列表watch_table[]中移除
void ril_event_del(struct ril_event * ev);

// 事件循环
void ril_event_loop();

接着分析ril_event .cpp文件：

#define LOG_TAG "RILC"

#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <fcntl.h>
#include <utils/Log.h>
#include <ril_event.h>
#include <string.h>
#include <sys/time.h>
#include <time.h>

#include <pthread.h>

// 使用互斥量mutex进行线程同步，可参见《Linux程序设计》相关章节
static pthread_mutex_t listMutex;
#define MUTEX_ACQUIRE() pthread_mutex_lock(&listMutex)
#define MUTEX_RELEASE() pthread_mutex_unlock(&listMutex)
#define MUTEX_INIT() pthread_mutex_init(&listMutex, NULL)
#define MUTEX_DESTROY() pthread_mutex_destroy(&listMutex)

// 两个timeval类型的值相加
#ifndef timeradd
#define timeradd(tvp, uvp, vvp)						\
	do {								\
		(vvp)->tv_sec = (tvp)->tv_sec + (uvp)->tv_sec;		\
		(vvp)->tv_usec = (tvp)->tv_usec + (uvp)->tv_usec;       \
		if ((vvp)->tv_usec >= 1000000) {			\
			(vvp)->tv_sec++;				\
			(vvp)->tv_usec -= 1000000;			\
		}							\
	} while (0)
#endif

// 两个timeval类型的值进行比较
#ifndef timercmp
#define timercmp(a, b, op)               \
        ((a)->tv_sec == (b)->tv_sec      \
        ? (a)->tv_usec op (b)->tv_usec   \
        : (a)->tv_sec op (b)->tv_sec)
#endif

// 两个timeval类型的值相减
#ifndef timersub
#define timersub(a, b, res)                           \
    do {                                              \
        (res)->tv_sec = (a)->tv_sec - (b)->tv_sec;    \
        (res)->tv_usec = (a)->tv_usec - (b)->tv_usec; \
        if ((res)->tv_usec < 0) {                     \
            (res)->tv_usec += 1000000;                \
            (res)->tv_sec -= 1;                       \
        }                                             \
    } while(0);
#endi

// 保存Rild中所有设备文件句柄，便于使用select函数完成事件的监听
static fd_set readFds;
// 记录readFds中最大fd值+1
static int nfds = 0;

// 为了统一管理ril事件，Android提供如下三个队列：
// 监控事件列表，需要检测的事件都需要先存入该列表中
static struct ril_event * watch_table[MAX_FD_EVENTS];

// timer事件队列，事件超时后即移入pending_list队列中
static struct ril_event timer_list;

// 待处理的事件队列，即事件已经触发，后续需要调用事件的回调函数
static struct ril_event pending_list;

#define DEBUG 0

#if DEBUG
#define dlog(x...) LOGD( x )
static void dump_event(struct ril_event * ev)
{
    dlog("~~~~ Event %x ~~~~", (unsigned int)ev);
    dlog("     next    = %x", (unsigned int)ev->next);
    dlog("     prev    = %x", (unsigned int)ev->prev);
    dlog("     fd      = %d", ev->fd);
    dlog("     pers    = %d", ev->persist);
    dlog("     timeout = %ds + %dus", (int)ev->timeout.tv_sec, (int)ev->timeout.tv_usec);
    dlog("     func    = %x", (unsigned int)ev->func);
    dlog("     param   = %x", (unsigned int)ev->param);
    dlog("~~~~~~~~~~~~~~~~~~");
}
#else
#define dlog(x...) do {} while(0)
#define dump_event(x) do {} while(0)
#endif

// 获取此刻timeval值
static void getNow(struct timeval * tv)
{
#ifdef HAVE_POSIX_CLOCKS
    struct timespec ts;
    clock_gettime(CLOCK_MONOTONIC, &ts);
    tv->tv_sec = ts.tv_sec;
    tv->tv_usec = ts.tv_nsec/1000;
#else
    gettimeofday(tv, NULL);
#endif
}

// 初始化指定的ril_event链表
static void init_list(struct ril_event * list)
{
    memset(list, 0, sizeof(struct ril_event));
    list->next = list;
    list->prev = list;
    list->fd = -1;
}

// 增加一个ril_event事件到ril_event队列头
static void addToList(struct ril_event * ev, struct ril_event * list)
{
    ev->next = list;
    ev->prev = list->prev;
    ev->prev->next = ev;
    list->prev = ev;
    dump_event(ev);
}

// 从ril_event队列中移除指定的ril_event
static void removeFromList(struct ril_event * ev)
{
    dlog("~~~~ Removing event ~~~~");
    dump_event(ev);

    ev->next->prev = ev->prev;
    ev->prev->next = ev->next;
    ev->next = NULL;
    ev->prev = NULL;
}

// 从watch_table[]中移除指定索引的事件
static void removeWatch(struct ril_event * ev, int index)
{
	// 索引index对应的事件置为空，同时事件ev的索引设为无效值-1
    watch_table[index] = NULL;
    ev->index = -1;

	// 将该事件对应的文件描述符句柄从readFds中清除
    FD_CLR(ev->fd, &readFds);

    if (ev->fd+1 == nfds) {
        int n = 0;

        for (int i = 0; i < MAX_FD_EVENTS; i++) {
            struct ril_event * rev = watch_table[i];

            if ((rev != NULL) && (rev->fd > n)) {
                n = rev->fd;
            }
        }
        nfds = n + 1;
        dlog("~~~~ nfds = %d ~~~~", nfds);
    }
}

// 遍历timer_list队列中的事件，当事件超时时间到时
// 将事件移除，并添加到pending_list队列中
static void processTimeouts()
{
    dlog("~~~~ +processTimeouts ~~~~");
    MUTEX_ACQUIRE();
    struct timeval now;
    struct ril_event * tev = timer_list.next;
    struct ril_event * next;

    getNow(&now);
    // walk list, see if now >= ev->timeout for any events

    dlog("~~~~ Looking for timers <= %ds + %dus ~~~~", (int)now.tv_sec, (int)now.tv_usec);
    while ((tev != &timer_list) && (timercmp(&now, &tev->timeout, >))) {
        // Timer expired
        dlog("~~~~ firing timer ~~~~");
        next = tev->next;
        removeFromList(tev);
        addToList(tev, &pending_list);
        tev = next;
    }
    MUTEX_RELEASE();
    dlog("~~~~ -processTimeouts ~~~~");
}

// 遍历监控列表watch_table[]中的事件，并将有数据可读的事件
// 添加到pending_list链表中，同时如果事件的persist不为true
// 则将该事件从watch_table[]中移除
static void processReadReadies(fd_set * rfds, int n)
{
    dlog("~~~~ +processReadReadies (%d) ~~~~", n);
    MUTEX_ACQUIRE();

    for (int i = 0; (i < MAX_FD_EVENTS) && (n > 0); i++) {
        struct ril_event * rev = watch_table[i];
        if (rev != NULL && FD_ISSET(rev->fd, rfds)) {
            addToList(rev, &pending_list);
            if (rev->persist == false) {
                removeWatch(rev, i);
            }
            n--;
        }
    }

    MUTEX_RELEASE();
    dlog("~~~~ -processReadReadies (%d) ~~~~", n);
}

// 依次调用待处理队列pending_list中的事件的回调函数
static void firePending()
{
    dlog("~~~~ +firePending ~~~~");
    struct ril_event * ev = pending_list.next;
    while (ev != &pending_list) {
        struct ril_event * next = ev->next;
        removeFromList(ev);
        ev->func(ev->fd, 0, ev->param);
        ev = next;
    }
    dlog("~~~~ -firePending ~~~~");
}

// 计算timer_list链表中下一个事件的新的超时时间
static int calcNextTimeout(struct timeval * tv)
{
    struct ril_event * tev = timer_list.next;
    struct timeval now;

    getNow(&now);

    // Sorted list, so calc based on first node
    if (tev == &timer_list) {
        // no pending timers
        return -1;
    }

    dlog("~~~~ now = %ds + %dus ~~~~", (int)now.tv_sec, (int)now.tv_usec);
    dlog("~~~~ next = %ds + %dus ~~~~",
            (int)tev->timeout.tv_sec, (int)tev->timeout.tv_usec);
    if (timercmp(&tev->timeout, &now, >)) {
        timersub(&tev->timeout, &now, tv);
    } else {
        // timer already expired.
        tv->tv_sec = tv->tv_usec = 0;
    }
    return 0;
}

// 初始化内部数据结构（互斥量、FD集合、三个事件队列）
void ril_event_init()
{
    MUTEX_INIT();

    FD_ZERO(&readFds);
    init_list(&timer_list);
    init_list(&pending_list);
    memset(watch_table, 0, sizeof(watch_table));
}

// 初始化一个ril事件
void ril_event_set(struct ril_event * ev, int fd, bool persist, ril_event_cb func, void * param)
{
    dlog("~~~~ ril_event_set %x ~~~~", (unsigned int)ev);
    memset(ev, 0, sizeof(struct ril_event));
    ev->fd = fd;
    ev->index = -1;
    ev->persist = persist;
    ev->func = func;
	ev->param = param;
	
	//linux的文件上锁函数，给文件描述符fd上非阻塞的文件锁
    fcntl(fd, F_SETFL, O_NONBLOCK);
}

// 将事件添加到监控列表watch_table[]中
void ril_event_add(struct ril_event * ev)
{
    dlog("~~~~ +ril_event_add ~~~~");
    MUTEX_ACQUIRE();
    for (int i = 0; i < MAX_FD_EVENTS; i++) {
        if (watch_table[i] == NULL) {
            watch_table[i] = ev;
            ev->index = i;
            dlog("~~~~ added at %d ~~~~", i);
            dump_event(ev);
            FD_SET(ev->fd, &readFds);
            if (ev->fd >= nfds) nfds = ev->fd+1;
            dlog("~~~~ nfds = %d ~~~~", nfds);
            break;
        }
    }
    MUTEX_RELEASE();
    dlog("~~~~ -ril_event_add ~~~~");
}

// 增加一个timer事件到timer_list链表中
void ril_timer_add(struct ril_event * ev, struct timeval * tv)
{
    dlog("~~~~ +ril_timer_add ~~~~");
    MUTEX_ACQUIRE();

    struct ril_event * list;
    if (tv != NULL) {
        // add to timer list
        list = timer_list.next;
        ev->fd = -1; // make sure fd is invalid

        struct timeval now;
        getNow(&now);
        timeradd(&now, tv, &ev->timeout);

        // 根据timeout值从小到大在链表中排序
        while (timercmp(&list->timeout, &ev->timeout, < )
                && (list != &timer_list)) {
            list = list->next;
        }
        // 循环结束后，list指向链表中第一个timeout值大于ev的事件
	// 将新加入的事件ev加到list此刻指向的事件前面
        addToList(ev, list);
    }

    MUTEX_RELEASE();
    dlog("~~~~ -ril_timer_add ~~~~");
}

// 将事件从watch_table[]中移除
void ril_event_del(struct ril_event * ev)
{
    dlog("~~~~ +ril_event_del ~~~~");
    MUTEX_ACQUIRE();

    if (ev->index < 0 || ev->index >= MAX_FD_EVENTS) {
        MUTEX_RELEASE();
        return;
    }

    removeWatch(ev, ev->index);

    MUTEX_RELEASE();
    dlog("~~~~ -ril_event_del ~~~~");
}

#if DEBUG
// 打印监控列表中可用的事件
static void printReadies(fd_set * rfds)
{
    for (int i = 0; (i < MAX_FD_EVENTS); i++) {
        struct ril_event * rev = watch_table[i];
        if (rev != NULL && FD_ISSET(rev->fd, rfds)) {
          dlog("DON: fd=%d is ready", rev->fd);
        }
    }
}
#else
#define printReadies(rfds) do {} while(0)
#endif

void ril_event_loop()
{
    int n;
    fd_set rfds;
    struct timeval tv;
    struct timeval * ptv;

    for (;;) {
        // make local copy of read fd_set
        memcpy(&rfds, &readFds, sizeof(fd_set));
	// 根据timer_list来计算select函数的等待时间
	// timer_list之前已按事件的超时时间排好序了
        if (-1 == calcNextTimeout(&tv)) {
            // no pending timers; block indefinitely
            dlog("~~~~ no timers; blocking indefinitely ~~~~");
            ptv = NULL;
        } else {
            dlog("~~~~ blocking for %ds + %dus ~~~~", (int)tv.tv_sec, (int)tv.tv_usec);
            ptv = &tv;
        }
        printReadies(&rfds);
	// 使用select函数实现多路IO复用
        n = select(nfds, &rfds, NULL, NULL, ptv);
        printReadies(&rfds);
        dlog("~~~~ %d events fired ~~~~", n);
        if (n < 0) {
            if (errno == EINTR) continue;

            LOGE("ril_event: select error (%d)", errno);
            // bail?
            return;
        }

        // Check for timeouts
        processTimeouts();
        // Check for read-ready
        processReadReadies(&rfds, n);
        // Fire away
        firePending();
    }
}