初探libOMX_Core

libOMX_Core.so是在xxxOMXPlugin的构造函数中打开的：

xxxOMXPlugin::xxxOMXPlugin()
 :mLibHandle(dlopen("libOMX_Core.so", RTLD_NOW)),
{
    if (mLibHandle != NULL) {
        mInit = (InitFunc)dlsym(mLibHandle, "xxxOMX_Init");
        mDeinit = (DeinitFunc)dlsym(mLibHandle, "xxxOMX_DeInit");

        mComponentNameEnum =
            (ComponentNameEnumFunc)dlsym(mLibHandle, "xxxOMX_ComponentNameEnum");

        mGetHandle = (GetHandleFunc)dlsym(mLibHandle, "xxxOMX_GetHandle");
        mFreeHandle = (FreeHandleFunc)dlsym(mLibHandle, "xxxOMX_FreeHandle");

        mGetRolesOfComponentHandle =
            (GetRolesOfComponentFunc)dlsym(
                    mLibHandle, "xxxOMX_GetRolesOfComponent");

        (*mInit)();
    }
}

这个是xxxOMXPlugin的构造函数的实现，最主要的是打开OMX_Core so，从dl找的symbol来看，OMX_Core实现了
xxxOMX_Init()、
xxxOMX_DeInit()、
xxxOMX_ComponentNameEnum()、
xxxOMX_GetHandle()、
xxxOMX_FreeHandle()、
xxxOMX_GetRolesOfComponent()

xxxOMX_Init

先看看xxxOMX_Init函数的实现：

OMX_ERRORTYPE xxxOMX_Init()
{
    ALOGD("[%s %s]\n", __FILE__, __func__);
    OMX_ERRORTYPE eError = OMX_ErrorNone;

    if(pthread_mutex_lock(&mutex) != 0)
    {
        ALOGE("%d :: Core: Error in Mutex lock\n",__LINE__);
        return OMX_ErrorUndefined;
    }

    count++;
    ALOGD("init count = %d\n", count);

    if (count == 1)
    {
        eError = RTKOMX_BuildComponentTable();
    }

    if(pthread_mutex_unlock(&mutex) != 0)
    {
        ALOGE("%d :: Core: Error in Mutex unlock\n",__LINE__);
        return OMX_ErrorUndefined;
    }
    return eError;
}

函数主要做了一件事RTKOMX_BuildComponentTable，该函数主要是准备componentTable，准备这个table是通过tComponentName这个数组实现的。我们先看看componentTable是存放怎样的元素：

ComponentTable componentTable[MAX_TABLE_SIZE];

typedef struct _ComponentTable {
        OMX_STRING name;
        OMX_U16 nRoles;
        OMX_STRING pRoleArray[MAX_ROLES];
        OMX_HANDLETYPE* pHandle[MAX_CONCURRENT_INSTANCES];
        int refCount;
}ComponentTable;

ComponentTable记录了每个Component的name，它的值有这些
(OMX.xxx.video.encoder、
OMX.xxx.video.decoder、
OMX.xxx.audio.encoder、
OMX.xxx.audio.decoder)，充当的角色数nRoles。每个角色对应的名字pRoleArray，它的取值大概如下：
video_encoder.avc、
audio_decoder.mp2
...
componentTable的创建过程如下(不再详述)：

OMX_ERRORTYPE xxxOMX_BuildComponentTable()
{
    OMX_ERRORTYPE eError = OMX_ErrorNone;

    OMX_CALLBACKTYPE sCallbacks;
    int j = 0;
    int numFiles = 0;
    int i;

    for (i = 0, numFiles = 0; i < MAXCOMP; i ++) {
        if (tComponentName[i][0] == NULL) {
            break;
        }
        if (numFiles <= MAX_TABLE_SIZE){
            for (j = 0; j < numFiles; j ++) {
                if (!strcmp(componentTable[j].name, tComponentName[i][0])) {
                    if (tComponentName[i][1] != NULL)
                    {
                        componentTable[j].pRoleArray[componentTable[j].nRoles] = tComponentName[i][1];
                        componentTable[j].nRoles ++;
                    }
                    break;
                }
            }
            if (j == numFiles) {
                if (tComponentName[i][1] != NULL){
                    componentTable[numFiles].pRoleArray[0] = tComponentName[i][1];
                    componentTable[numFiles].nRoles = 1;
                }
                strcpy(compName[numFiles], tComponentName[i][0]);
                componentTable[numFiles].name = compName[numFiles];
                componentTable[numFiles].refCount = 0;
                numFiles ++;
            }
        }
    }
    tableCount = numFiles;
    ALOGD("build tableCount = %lu\n", tableCount);
    if (eError != OMX_ErrorNone){
        ALOGE("Could not build Component Table\n");
    }

    return eError;
}

xxxOMX_GetHandle

xxxOMX_GetHandle是在xxxOMXPlugin中的makeComponentInstance函数中调用的：

OMX_ERRORTYPE RTKOMXPlugin::makeComponentInstance(
        const char *name,
        const OMX_CALLBACKTYPE *callbacks,
        OMX_PTR appData,
        OMX_COMPONENTTYPE **component) {
    if (mLibHandle == NULL) {
        return OMX_ErrorUndefined;
    }

    return (*mGetHandle)(
            reinterpret_cast<OMX_HANDLETYPE *>(component),
            const_cast<char *>(name),
            appData, const_cast<OMX_CALLBACKTYPE *>(callbacks));
}

xxxOMX_GetHandle函数的实现如下：

OMX_ERRORTYPE RTKOMX_GetHandle( OMX_HANDLETYPE* pHandle, OMX_STRING cComponentName,
    OMX_PTR pAppData, OMX_CALLBACKTYPE* pCallBacks)
{
    ALOGD("[%s %s]\n", __FILE__, __func__);

    static const char prefix[] = "lib";
    static const char postfix[] = ".so";
    OMX_ERRORTYPE (*pComponentInit)(OMX_HANDLETYPE*);
    OMX_ERRORTYPE err = OMX_ErrorNone;
    OMX_COMPONENTTYPE *componentType;
    const char* pErr = dlerror();

    if(pthread_mutex_lock(&mutex) != 0)
    {
        ALOGE("%d :: Core: Error in Mutex lock\n",__LINE__);
        return OMX_ErrorUndefined;
    }

    if ((NULL == cComponentName) || (NULL == pHandle) || (NULL == pCallBacks)) {
        err = OMX_ErrorBadParameter;
        goto UNLOCK_MUTEX;
    }

    if(strlen(cComponentName) >= MAXNAMESIZE) {
        err = OMX_ErrorInvalidComponentName;
        goto UNLOCK_MUTEX;
    }

    unsigned int i = 0;
    for(i=0; i< COUNTOF(pModules); i++) {
        if(pModules[i] == NULL) break;
    }
    if(i == COUNTOF(pModules)) {
        err = OMX_ErrorInsufficientResources;
        goto UNLOCK_MUTEX;
    }

    int refIndex = 0;
    for (refIndex=0; refIndex < MAX_TABLE_SIZE; refIndex++) {
        if (strcmp(componentTable[refIndex].name, cComponentName) == 0) {
            ALOGD("Found component %s with refCount %d\n",
                  cComponentName, componentTable[refIndex].refCount);

            if (componentTable[refIndex].refCount >= getMaxRefCnt(cComponentName)) {
                err = OMX_ErrorInsufficientResources;
                ALOGE("Max instances(%d) of component %s already created.\n", componentTable[refIndex].refCount, cComponentName);
                goto UNLOCK_MUTEX;
            } else {
                char buf[sizeof(prefix) + MAXNAMESIZE + sizeof(postfix)];
                strcpy(buf, prefix);
#if 0 /* luke.lin */
                size_t length = strlen(cComponentName);
                if (!strcmp( cComponentName + length - 7, ".secure")) {
                    length -= 7;
                }
                strncat(buf, cComponentName, length);
#else
                strcat(buf, cComponentName);
#endif
                strcat(buf, postfix);

                pModules[i] = dlopen(buf, RTLD_LAZY | RTLD_GLOBAL);
                if( pModules[i] == NULL ) {
                    ALOGE("dlopen %s failed because %s\n", buf, dlerror());
                    err = OMX_ErrorComponentNotFound;
                    goto UNLOCK_MUTEX;
                }

                pComponentInit = dlsym(pModules[i], "OMX_ComponentInit");
                pErr = dlerror();
                if( (pErr != NULL) || (pComponentInit == NULL) ) {
                    ALOGE("%d:: dlsym failed for module %p\n", __LINE__, pModules[i]);
                    err = OMX_ErrorInvalidComponent;
                    goto CLEAN_UP;
                }

                *pHandle = malloc(sizeof(OMX_COMPONENTTYPE));
                if(*pHandle == NULL) {
                    err = OMX_ErrorInsufficientResources;
                    ALOGE("%d:: malloc of pHandle* failed\n", __LINE__);
                    goto CLEAN_UP;
                }

                pComponents[i] = *pHandle;
                componentType = (OMX_COMPONENTTYPE*) *pHandle;
                componentType->nSize = sizeof(OMX_COMPONENTTYPE);
                err = (*pComponentInit)(*pHandle);
                if (OMX_ErrorNone == err) {
                    err = (componentType->SetCallbacks)(*pHandle, pCallBacks, pAppData);
                    if (err != OMX_ErrorNone) {
                        ALOGE("%d :: Core: SetCallBack failed %d\n",__LINE__, err);
                        goto CLEAN_UP;
                    }
                    componentTable[refIndex].pHandle[componentTable[refIndex].refCount] = *pHandle;
                    componentTable[refIndex].refCount += 1;
                    goto UNLOCK_MUTEX;
                }
                else if (err == OMX_ErrorInsufficientResources) {
                        ALOGE("%d :: Core: Insufficient Resources for Component %d\n",__LINE__, err);
                        goto CLEAN_UP;
                }
            }
        }
    }

    err = OMX_ErrorComponentNotFound;
    goto UNLOCK_MUTEX;
CLEAN_UP:
    if(*pHandle != NULL)
    {
        free(*pHandle);
        *pHandle = NULL;
    }
    pComponents[i] = NULL;
    dlclose(pModules[i]);
    pModules[i] = NULL;

UNLOCK_MUTEX:
    if(pthread_mutex_unlock(&mutex) != 0)
    {
        ALOGE("%d :: Core: Error in Mutex unlock\n",__LINE__);
        err = OMX_ErrorUndefined;
    }
    return (err);
}