https://github.com/zytc2009/BigTeam_learning
分类： Java
2010-12-01 11:53:50
前面我们说了文件的打开，发送数据给下一个peer，但是我们还是不明白文件的格式是如何识别的，因为文件的种类繁多，文件的识别就会很麻烦，并且还要考虑到可扩展性，所以这个文件的识别是以插件的形式来存在的，这里我们简要的说一下，这个插件的框架。
由于文件的格式很多，而且标准也很多，很难肯定某一文件就是某种的格式，因而就引入一个确信度的概念。
typedef Oscl_Vector
typedef enum _PVMFRecognizerConfidence
{
PVMFRecognizerConfidenceNotCertain, // 100% sure not the format
PVMFRecognizerConfidenceNotPossible, // Maybe not the format
PVMFRecognizerConfidenceUnknown, // Not sure one way or the other
PVMFRecognizerConfidencePossible, // Maybe the format
PVMFRecognizerConfidenceCertain // 100% sure of the format
} PVMFRecognizerConfidence;
然后是文件识别的结果：
class PVMFRecognizerResult
{
public:
PVMFRecognizerResult()
{
};
// Copy constructor for use in Oscl_Vector
PVMFRecognizerResult(const PVMFRecognizerResult& aSrc)
{
iRecognizedFormat = aSrc.iRecognizedFormat;
iRecognitionConfidence = aSrc.iRecognitionConfidence;
// iRecognizerSubFormatList=aSrc.iRecognizerSubFormatList;
};
~PVMFRecognizerResult()
{
};
// The format of interest as a MIME string
OSCL_HeapString
// The confidence level of recognition
PVMFRecognizerConfidence iRecognitionConfidence;
// If the format is a container format, the format of content within
// Oscl_Vector
};
格式和确信度。
然后就是一个事件的监控者Observer。
/**
* PVMFRecognizerCommmandHandler Class
*
* PVMFRecognizerCommmandHandler is the PVMF Recognizer observer class for notifying the
* status of asynchronous requests. The API provides a mechanism for the status of each
* command to be passed back along with context specific information where applicable.
* User of the recognizer registry must have a class derived from PVMFNodeCmdStatusObserver
* and implement the pure virtual function in order to receive event notifications from
* PVMF Recognizer Registry.
**/
class PVMFRecognizerCommmandHandler
{
public:
/**
* Handle an event that has been generated.
*
* @param aResponse
* The response to a previously issued command
*/
virtual void RecognizerCommandCompleted(const PVMFCmdResp& aResponse) = 0;
virtual ~PVMFRecognizerCommmandHandler() {}
};
#endif // PVMF_RECOGNIZER_TYPES_H_INCLUDED
这些都只是纯虚类。
文件识别，一般都是读取文件中的某些特殊的字节，然后才能做判断的，由于不同的文件读取的地方不同，并且识别的规则也是不同，所以定义一个基本的接口。
class PVMFRecognizerPluginInterface
{
public:
/**
* Virtual destructor for the plug-in. All plug-ins should perform any clean up here
**/
virtual ~PVMFRecognizerPluginInterface()
{
};
/**
* This methods returns a list of format(s) that this plug-in can recognize. Each supported format
* is represented by a MIME string.
*
* @param aSupportedFormatsList
* Reference to a list of MIME strings which will be filled in with list of formats that the plug-in can recognize.
*
* @exception This method can leave with one of the following error codes
* OsclErrNoMemory if memory cannot be allocated for the format list
*
* @returns A PVMF status code to report result of method
**/本插件支持下面的一些格式的识别，以一个列表的形式返回
注意我们的文件识别都是以插件的形式存在的，这样就可以保证文件识别的可扩展性，每一个插件都必须从这个接口来继承，另外还必须有一个类统一管理这些插件，如插件的查找和注册
virtual PVMFStatus SupportedFormats(PVMFRecognizerMIMEStringList& aSupportedFormatsList) = 0;
/**
* This method determines the the specified content is or is not one of the formats recognized by this plug-in
*
* @param aSourceDataStreamFactory
* A reference to a PVMFDataStreamFactory representing the content to recognize
* @param aFormatHint
* An optional input parameter expressed as a list of MIME string which provides a priori hint for the format
* of the content specified by aSourceDataStreamFactory.
* @param aRecognizerResult
* An output parameter which is a reference to a vector of PVMFRecognizerResult that will contain the recognition
* result if the Recognize() method succeeds.
*
* @exception This method can leave with one of the following error codes
*
* @returns A PVMF status code to report result of method
**/
//给定一个数据源让你去识别，有一个优先考虑的格式列表参数，返回的是一个识别结果的列表，列出可能的格式和确信度。
virtual PVMFStatus Recognize(PVMFDataStreamFactory& aSourceDataStreamFactory,
PVMFRecognizerMIMEStringList* aFormatHint,
Oscl_Vector
/**
* This method returns the mininum required bytes in datastream for this plug-in
* to be able to recognize its supported formats.
*
* @param aBytes[out]
* A reference to a minimum required bytes
*
* @returns A PVMF status code to report result of method.
* PVMFSuccess in case of success and PVMFFailure otherwise.
**///或者识别所需的最小字节数
virtual PVMFStatus GetRequiredMinBytesForRecognition(uint32& aBytes) = 0;
};
每一个插件都需要占用一定内存，因而就有下面的定义：一个插件的工厂的基类，每一个插件都要有一个这样的工厂接口来创建和删除某一个插件。
/**
* An abstract base class to create and destroy a recognizer plug-in. Every recognizer plug-in should have
* an associated factory class to provide a standard way to create and destroy the plug-in.
**/
class PVMFRecognizerPluginFactory: public HeapBase
{
public:
/**
* Virtual destructor for the plug-in factory. All plug-in factory should perform any clean up here
**/
virtual ~PVMFRecognizerPluginFactory()
{
};
/**
* This method instantiates and returns the recognizer plug-in that the factory is associated with.
*
* @exception This method can leave with one of the following error codes
* OsclErrNoMemory if memory cannot be allocated for the recognizer plug-in
* @returns A pointer to the recognizer plug-in instance if creation is successful.
**/
virtual PVMFRecognizerPluginInterface* CreateRecognizerPlugin() = 0;
/**
* This method destroys the specified recognizer plug-in pointer as the particular recognizer plug-in
* the factory is associated with.
*
* @param aPlugIn
* A pointer to the recognizer plug-in that should be destroyed.
*
* @exception This method can leave with one of the following error codes
*
* @returns None
**/
virtual void DestroyRecognizerPlugin(PVMFRecognizerPluginInterface* aPlugIn) = 0;
};
然后就是一个模板的定义，因为插件很多，这里我们写一个简单的模板：
/**
* Basic templatized recognizer plug-in factory. Can be used if the recognizer plug-in only needs
* to be instantiated and destroyed by just new and delete, respectively and no other functionality
* is needed from the factory class.
**/
template
class PVMFRecognizerPluginFactoryBasic : public PVMFRecognizerPluginFactory
{
public:
virtual ~PVMFRecognizerPluginFactoryBasic()
{
};
PVMFRecognizerPluginInterface* CreateRecognizerPlugin()
{
T* plugin = OSCL_NEW(T, ());
return plugin;
};
void DestroyRecognizerPlugin(PVMFRecognizerPluginInterface* aPlugIn)
{
T* plugin = (T*)aPlugIn;
OSCL_DELETE(plugin);
};
};
这样关于插件的基类，我们基本搞定，下面的就是这么多插件在一起如何去管理。这里就是一个静态类（static）。负责插件的注册和注销，并且负责文件的的寻找，来了文件，历遍所有注册过的插件来找到最匹配的格式。这和微软的DirectShow框架极为相似，不过微软的Filter是这侧到注册表里面去了，并且，微软Filter的概念不仅仅是文件的识别，在微软的注册表中，有一项就是Media Type，规定了系统所能够识别的文件类型，每一个类型都要有匹配码，例如前面八个字节是什么，后面四个字节是什么，这些都是在注册表中，注册的另外的一个就是打开这个文件所需的Source Filter的ID，这样要播放的文件的时候按照一定优先级匹配这些注册信息就行了。
这里关于插件的管理有一个单独的静态类，静态类的特点就是不管类是不是存在，这个东西都是存在的，并且全局可访问。这才是我们识别的关键代码：
/**
* A class of static methods that provides the interface to the PVMF recognizer registry..
* With these static methods, the recognizer registry can be initialized and shutdown, recognizer
* plug-ins can be registered and unregistered, and format of a content can be recognized.
**/
class PVMFRecognizerRegistry
{
public:
/**
格式的注册信息的初始化，因为我们知道，一种格式的识别，都会注册相应的信息，识别器就是通过这些信息的历遍，找出对应的文件。在使用识别器之前，最先就是初始化。
* This static method initializes the recognizer registry for use. This method must be called once
* and succeed before calling any other methods from PVMFRecognizerRegistry.
*
* @exception This method can leave with one of the following error codes
* OsclErrNoMemory if memory cannot be allocated for the registry implementation
* @returns A PVMF status code to report result of method
**/
OSCL_IMPORT_REF static PVMFStatus Init();
/**
使用完之后，就要清空
* This static methods shuts down and cleans up the recognizer registry. This method must be called once
* after there is no more use for the recognizer registry to properly release the memory allocated for the
* registry
**/
OSCL_IMPORT_REF static void Cleanup();
/**
一种媒体格式识别信息的添加，实际上就是添加一个PVMFRecognizerPluginFactory，前面我们说过每一种格式都会有其对应的PVMFRecognizerPluginFactory。
* This static method adds the specified recognizer plug-in factory to the list of available recognizers.
* The passed-in plug-in factory would be used to create and destroy the recognizer plug-in in the Recognize() methods.
* The passed-in plug-in factory reference must be valid until it is removed from the list by the RemovePlugin() method.
*
* @param aPluginFactory
* A reference to a recognizer plug-in factory to add to the list of registered recognizers
*
* @exception This method can leave with one of the following error codes
* OsclErrNoMemory if memory cannot be allocated for vector holding the plug-in factory pointers
* @returns A PVMF status code to report result of method
**/
OSCL_IMPORT_REF static PVMFStatus RegisterPlugin(PVMFRecognizerPluginFactory& aPluginFactory);
/** 注销某一种格式，将某一种识别的信息从注册信息列表中剔除
* This static method removes the specified recognizer plug-in factory from the list of available recognizers.
* The passed-in plug-in factory must have been added before with RegisterPlugin() for this method to succeed.
* After the plug-in factory is successfully removed, the factory instance can be deleted.
*
* @param aPluginFactory
* A reference to a recognizer plug-in factory to remove from the list of registered recognizers
*
* @returns A PVMF status code to report result of method
**/
OSCL_IMPORT_REF static PVMFStatus RemovePlugin(PVMFRecognizerPluginFactory& aPluginFactory);
/**
* This static method creates a recognition session with the recognizer framework.
*创建一个识别的会话，
* @param aSessionId 返回一个会话的ID
* A reference to a PVMFSessionId which will be set to the session's unique identifier when this method
* completes successfully.
* @param aCmdHandler 给它一个识别的观察者，也就是消息的监控者
* A reference to a PVMFRecognizerCommmandHandler which will receive asynchronous command completion notification.
*
* @returns A PVMF status code to report result of method
**/
OSCL_IMPORT_REF static PVMFStatus OpenSession(PVMFSessionId& aSessionId, PVMFRecognizerCommmandHandler& aCmdHandler);
/**
* This static method shuts down a recognition session with the recognizer framework.
*关闭一个会话
* @param aSessionId
* The unique identifier of the session to close
*
* @returns A PVMF status code to report result of method
**/
OSCL_IMPORT_REF static PVMFStatus CloseSession(PVMFSessionId aSessionId);
/**开始识别，开始识别的开始就需要一个数据的来源、然后是优先考虑的格式、识别结果的存储、
* This static method asynchronously determines the format of the specified content using the currently registered
* recognizer plug-ins. When the recognizer request completes, the user would be notified via the PVMFRecognizerCommandHandler
* callback handler set when opening the session.
*
* @param aSessionId
* The unique identifier for the recognizer session
* @param aSourceDataStreamFactory 数据的来源
* A reference to a PVMFDataStreamFactory representing the content to recognize
* @param aFormatHintList优先考虑的格式
* An optional input parameter expressed as a list of MIME string which provides a priori hint for the format
* of the content specified by aSourceDataStreamFactory.
* @param aRecognizerResult结果的存储
* An output parameter which is a reference to a vector of PVMFRecognizerResult that will contain the recognition
* result if the Recognize() method succeeds.
* @param aCmdContext
* Optional pointer to opaque data that will be returned in the command completion response，识别上下文的返回
* @param aTimeout 识别的时间限制
* Optional timeout value for the recognition request. If the recognition operation takes more time than the timeout
* value, the operation will be cancelled with PVMFErrTimeout status code. If the timeout value is set to 0, the
* recognition operation will go to completion.
*
* @exception This method can leave with one of the following error codes
* OsclErrNoMemory if memory cannot allocated to process this request
* OsclErrArgument if one or more of the passed-in parameters is invalid
*
* @returns A PVMF command ID for the recognize request
**/
OSCL_IMPORT_REF static PVMFCommandId Recognize(PVMFSessionId aSessionId, PVMFDataStreamFactory& aSourceDataStreamFactory, PVMFRecognizerMIMEStringList* aFormatHintList,
Oscl_Vector
/**取消前一个异步的识别操作
* This static method cancels a previously issued asynchronous request that hasn't completed yet.
*
* @param aSessionId
* The unique identifier for the recognizer session
* @param aCommandToCancelId
* Unique identifier for the asynchronous request to cancel.
* @param aCmdContext
* Optional pointer to opaque data that will be returned in the command completion response
*
* @exception This method can leave with one of the following error codes
* OsclErrNoMemory if memory cannot allocated to process this request
* OsclErrArgument if one or more of the passed-in parameters is invalid
*
* @returns A PVMF command ID for the cancel request
**/
OSCL_IMPORT_REF static PVMFCommandId CancelCommand(PVMFSessionId aSessionId, PVMFCommandId aCommandToCancelId, OsclAny* aCmdContext = NULL);
};
这样我们的识别文件格式的框架就完成了。下面看一些具体的实现。
很遗憾，在OSDL中，我们已经定义好了一个类似于微软注册表的东西，它存在与OSDL中，在OSDL之上的任何代码都是可以访问的。
class OsclTLSRegistry
{
public:
/*
** Get an entry
** @param ID: identifier
** @param error (output) 0 for success or an error from TPVBasePanicEnum
** @returns: the entry value
*/
OSCL_IMPORT_REF static OsclAny* getInstance(uint32 ID, int32 &error);
/*
** Set an entry
** @param ID: identifier
** @param error (output) 0 for success or an error from TPVBasePanicEnum
** @returns: the entry value
*/
OSCL_IMPORT_REF static void registerInstance(OsclAny* ptr, uint32 ID, int32 &error);
private:
OsclTLSRegistry()
{}
typedef OsclAny* registry_type;
typedef registry_type* registry_pointer_type;
#if ( OSCL_TLS_IS_KEYED)
class TKeyItem
{
public:
TKeyItem(): iTlsKey(NULL), iThreadId(0)
{}
TOsclTlsKey *iTlsKey;
TOsclTlsThreadId iThreadId;
};
class TlsKeyTable
{
public:
TlsKeyTable(): iNumKeys(0)
{}
_OsclBasicLock iLock;
uint32 iNumKeys;
TKeyItem iKeys[OSCL_TLS_MAX_THREADS];
};
//The key table is a global variable.
static TlsKeyTable* iTlsKeyTable;
static void GetThreadId(TOsclTlsThreadId &threadId, int32&);
static TOsclTlsKey* LookupTlsKey(int32&);
static bool SaveTlsKey(TOsclTlsKey* key, int32&);
static bool RemoveTlsKey(Oscl_DefAlloc& alloc, TOsclTlsKey* key, int32&);
#endif
private:
OSCL_IMPORT_REF static void initialize(Oscl_DefAlloc &alloc, int32 &error);
OSCL_IMPORT_REF static void cleanup(Oscl_DefAlloc &alloc, int32 &error);
friend class OsclBase;
};
这个类的实现可以参见具体的代码，所以这里我们就不去多说。这里我们在注册信息中填入的是一个什么呢？
我们看静态的初始化函数。
OSCL_EXPORT_REF PVMFStatus PVMFRecognizerRegistry::Init()
{
// Check that there is no existing registry
PVMFRecognizerRegistryImpl* pvrecregimpl = OSCL_STATIC_CAST(PVMFRecognizerRegistryImpl*, PVMFRECOGNIZER_REGISTRY::getInstance(PVMFRECOGNIZER_REGISTRY_ID));
// 如果存在，那么我就不用注册这个一项了
if (pvrecregimpl != NULL)
{
// Registry is already present so no need to instantiate again
// Just increment the refcount
(pvrecregimpl->iRefCount)++;
return PVMFSuccess;
}
// Instantiate the registry implementation，否则就开始分配新的空间开始注册
Oscl_TAlloc
pvrecregimpl = OSCL_ALLOC_NEW(talloc, PVMFRecognizerRegistryImpl, ());
// Save it on singleton or TLS
PVMFRECOGNIZER_REGISTRY::registerInstance(pvrecregimpl, PVMFRECOGNIZER_REGISTRY_ID);
return PVMFSuccess;
}
继续往下面讲之前，我觉得我们可以看一下PVMFRecognizerRegistryImpl，这个是怎么实现的，PVMFRecognizerRegistryImpl是我们注册表中保存的一个东东。主要实现文件的识别，包含很多的信息。我以前以为只有变量才能注册的，其实函数也能注册的，函数代码的空间也是数据，是数据就有指针，所以整个类也是可以注册的。注册后，如果要清空，那么就要调用Cleanup，
OSCL_EXPORT_REF void PVMFRecognizerRegistry::Cleanup()
{
// Retrieve the registry implementation instance from singleton or TLS and destroy it
首先单件模式，返回我们注册的PVMFRecognizerRegistryImpl指针，这个指针指向的内容是存在的，因为我们前面在初始化的时候就分配了内存
PVMFRecognizerRegistryImpl* pvrecregimpl = OSCL_STATIC_CAST(PVMFRecognizerRegistryImpl*, PVMFRECOGNIZER_REGISTRY::getInstance(PVMFRECOGNIZER_REGISTRY_ID));
if (pvrecregimpl != NULL)
{
// First decrement the refcount，直接自减就行了，自身负责分配
--(pvrecregimpl->iRefCount);
// If the resulting refcount is 0, then delete the instance
if ((pvrecregimpl->iRefCount) <= 0)
{
Oscl_TAlloc
OSCL_ALLOC_DELETE(pvrecregimpl, talloc, PVMFRecognizerRegistryImpl);
// Unregister by putting NULL pointer in singleton or TLS 释放后，注意把注册表中的信息清空
PVMFRECOGNIZER_REGISTRY::registerInstance(NULL, PVMFRECOGNIZER_REGISTRY_ID);
}
}
else
{
// Registry has already been cleaned up so nothing to do
}
}
然后就是注册我们的文件识别组件
OSCL_EXPORT_REF PVMFStatus PVMFRecognizerRegistry::RegisterPlugin(PVMFRecognizerPluginFactory& aPluginFactory)
{
PVMFRecognizerRegistryImpl* pvrecregimpl = OSCL_STATIC_CAST(PVMFRecognizerRegistryImpl*, PVMFRECOGNIZER_REGISTRY::getInstance(PVMFRECOGNIZER_REGISTRY_ID));
if (pvrecregimpl != NULL)
{
return pvrecregimpl->RegisterPlugin(aPluginFactory);
}
else
{
// Registry hasn't been initialized yet. Assert
OSCL_ASSERT(false);
return PVMFErrNotReady;
}
}
其实很简单，调用对应的成员就行了。
下面的几个函数基本上都是这样子了，RemovePlugin、OpenSession、CloseSession、Recognize、CancelCommand。
下面我们看看
PVMFRecognizerRegistryImpl的实现。
因为文件的识别是一个比较“卡”的过程，为了不让我们的软件给人很卡的感官，我们这里把这个类另辟一个线程来进行，并且以异步的方式来调用，通过命令。
识别的命令有下面的两种类型：
/**
* PVMFRecRegImplCommandType enum
*
* Enumeration of commands that can be issued to the PVMF Recognizer Registry
*
**/
typedef enum
{
PVMFRECREG_COMMAND_RECOGNIZE = 1,
PVMFRECREG_COMMAND_CANCELCOMMAND,
} PVMFRecRegImplCommandType;
一个就是开始识别，一个就是取消识别。
class PVMFRecRegSessionInfo
{
public:
PVMFRecRegSessionInfo()
{
};
PVMFRecRegSessionInfo(const PVMFRecRegSessionInfo& aSrc)
{
iRecRegSessionId = aSrc.iRecRegSessionId;
iRecRegCmdHandler = aSrc.iRecRegCmdHandler;
};
~PVMFRecRegSessionInfo()
{
};
PVMFSessionId iRecRegSessionId;
PVMFRecognizerCommmandHandler* iRecRegCmdHandler;
};
识别的一个信息的保存，一个事识别的sessionID，一个事事件处理。
下面就是一个命令的具体的封装，包含一个参数的列表/**
* PVMFRecRegImplCommand Class
*
* PVMFRecRegImplCommand class is a data class to hold issued commands inside the recognizer registry impl
**/
class PVMFRecRegImplCommand
{
public:
/**
* The constructor for PVMFRecRegImplCommand which allows the data values to be set.
*
* @param aCmdType The command type value for this command.
* @param aCmdId The command ID assigned for this command.
* @param aContextData The pointer to the passed-in context data for this command.
* @param aParamVector The optional pointer to a list of parameters
*
* @returns None
**/初始化就是一个参数列表
PVMFRecRegImplCommand(PVMFSessionId aSessionId, int32 aCmdType, PVMFCommandId aCmdId, OsclAny* aContextData = NULL,
Oscl_Vector
iSessionId(aSessionId), iCmdType(aCmdType), iCmdId(aCmdId), iContextData(aContextData), iAPICommand(aAPICommand)
{
iParamVector.clear();
if (aParamVector)
{
iParamVector = *aParamVector;
}
}
/**
* The copy constructor for PVMFRecRegImplCommand. Used mainly for Oscl_Vector.
*
* @param aCmd The reference to the source PVMFRecRegImplCommand to copy the data values from.
*
* @returns None
**/
PVMFRecRegImplCommand(const PVMFRecRegImplCommand& aCmd)
{
iSessionId = aCmd.iSessionId;
iCmdType = aCmd.iCmdType;
iCmdId = aCmd.iCmdId;
iContextData = aCmd.iContextData;
iAPICommand = aCmd.iAPICommand;
iParamVector = aCmd.iParamVector;
}
/**
* This function returns the session ID for the command
*
* @returns The session ID value for this command.
**/
PVMFSessionId GetSessionId()const
{
return iSessionId;
}
/**
* This function returns the stored command type value.
*
* @returns The signed 32-bit command type value for this command.
**/
int32 GetCmdType()const
{
return iCmdType;
}
/**
* This function returns the stored command ID value.
*
* @returns The PVMFCommandId value for this command.
**/
PVMFCommandId GetCmdId()const
{
return iCmdId;
}
/**
* This function returns the stored context data pointer.
*
* @returns The pointer to the context data for this command
**/
OsclAny* GetContext()const
{
return iContextData;
}
/**
* This function tells whether the command is an API command or not
*
* @returns true if API command, false if not.
**/
bool IsAPICommand()const
{
return iAPICommand;
}
/**
* This function returns the command parameter from the specified index.
* If the specified index is not available, empty parameter will be returned
*
* @param aIndex The index of the parameter to return
*
* @returns The stored parameter for this command
**/
PVMFRecRegImplCommandParamUnion GetParam(uint32 aIndex)const
{
if (aIndex >= iParamVector.size())
{
PVMFRecRegImplCommandParamUnion param;
oscl_memset(¶m, 0, sizeof(PVMFRecRegImplCommandParamUnion));
return param;
}
else
{
return iParamVector[aIndex];
}
}
bool operator==(const PVMFRecRegImplCommand& x)const
{
return iCmdId == x.iCmdId;
}
PVMFSessionId iSessionId;
int32 iCmdType;
PVMFCommandId iCmdId;
OsclAny* iContextData;
bool iAPICommand;
Oscl_Vector
};
上面就是一个带参数的识别命令。
然后有一个优先级的比较：
class PVMFRecRegImplCommandCompareLess
{
public:
/**
* The algorithm used in OsclPriorityQueue needs a compare function
* that returns true when A's priority is less than B's
* @return true if A's priority is less than B's, else false
*/
int compare(PVMFRecRegImplCommand& a, PVMFRecRegImplCommand& b) const
{
int a_pri = PVMFRecRegImplCommandCompareLess::GetPriority(a);
int b_pri = PVMFRecRegImplCommandCompareLess::GetPriority(b);
if (a_pri < b_pri)
{
// Higher priority
return true;
}
else if (a_pri == b_pri)
{
// Same priority so look at the command ID to maintain FIFO
return (a.GetCmdId() > b.GetCmdId());
}
else
{
// Lower priority
return false;
}
}
/**
* Returns the priority of each command
* @return A 0-based priority number. A lower number indicates lower priority.
*/
static int GetPriority(PVMFRecRegImplCommand& aCmd)
{
switch (aCmd.GetCmdType())
{
case PVMFRECREG_COMMAND_RECOGNIZE:
return 5;
case PVMFRECREG_COMMAND_CANCELCOMMAND:
return 3;
default:
return 0;
}
}
};
如何识别的？
/**
* Implementation of the recognizer registry. The recognizer interface class should only
* use this class.
**/
这里为什么要从PvmiDataStreamObserver来继承，因为我们的识别就必须读取一部分的字节，必然会有相关的data数据流的操作，这里是一个简单的事件监控。为什么要从OsclTimerObject，因为我们识别是单开线程的，并且识别有一个时间的上线。
class PVMFRecognizerRegistryImpl : public OsclTimerObject,
public PvmiDataStreamObserver
{
public:
PVMFRecognizerRegistryImpl();
~PVMFRecognizerRegistryImpl();
注册和注销识别插件
PVMFStatus RegisterPlugin(PVMFRecognizerPluginFactory& aPluginFactory);
PVMFStatus RemovePlugin(PVMFRecognizerPluginFactory& aPluginFactory);
PVMFStatus OpenSession(PVMFSessionId& aSessionId, PVMFRecognizerCommmandHandler& aCmdHandler);
PVMFStatus CloseSession(PVMFSessionId aSessionId);
识别
PVMFCommandId Recognize(PVMFSessionId aSessionId, PVMFDataStreamFactory& aSourceDataStreamFactory, PVMFRecognizerMIMEStringList* aFormatHint,
Oscl_Vector
PVMFCommandId CancelCommand(PVMFSessionId aSessionId, PVMFCommandId aCommandToCancelId, OsclAny* aCmdContext);
// Reference count for the registry implementation
int32 iRefCount; 注册的Plug个数
private:
这个我怀疑是这样的，同时可能有多个识别的操作，那么就需要列表处理
PVMFSessionId iNextSessionId;
PVMFCommandId iNextCommandId;
// From OsclTimerObject
void Run();
// Vector to hold the active sessions
Oscl_Vector
// Vector to hold the available recognizer plug-in
Oscl_Vector
int32 FindPluginFactory(PVMFRecognizerPluginFactory& aFactory);
PVMFRecognizerPluginInterface* CreateRecognizerPlugin(PVMFRecognizerPluginFactory& aFactory);
void DestroyRecognizerPlugin(PVMFRecognizerPluginFactory& aFactory, PVMFRecognizerPluginInterface* aPlugin);
// Vector to hold pending, current, and to-cancel commands
OsclPriorityQueue
Oscl_Vector
Oscl_Vector
PVMFCommandId
AddRecRegCommand(PVMFSessionId aSessionId, int32 aCmdType, OsclAny*
aContextData = NULL, Oscl_Vector
void CompleteCurrentRecRegCommand(PVMFStatus aStatus, const uint32 aCurrCmdIndex = 0, PVInterface* aExtInterface = NULL);
bool FindCommandByID(Oscl_Vector
// Command handling functions
void DoRecognize();
void CompleteRecognize(PVMFStatus aStatus);
void DoCancelCommand(PVMFRecRegImplCommand& aCmd);
PVMFDataStreamFactory* iDataStreamFactory;
PVMIDataStreamSyncInterface* iDataStream;
PvmiDataStreamSession iDataStreamSessionID;
PvmiDataStreamCommandId iRequestReadCapacityNotificationID;
PVMFStatus GetMaxRequiredSizeForRecognition(uint32& aMaxSize);
PVMFStatus GetMinRequiredSizeForRecognition(uint32& aMinSize);
PVMFStatus CheckForDataAvailability();
//logger
PVLogger* iLogger;
/* From PvmiDataStreamObserver */
void DataStreamCommandCompleted(const PVMFCmdResp& aResponse);
void DataStreamInformationalEvent(const PVMFAsyncEvent& aEvent);
void DataStreamErrorEvent(const PVMFAsyncEvent& aEvent);
bool oRecognizePending;
PVMFStatus iDataStreamCallBackStatus;
};
这个函数具体是如何实现的，有兴趣的可以继续看一下，我小看了一下，基本上就是一个for循环识别文件的格式。并且这种框架很容易扩展新的文件格式。不错不错。具体的文件plug怎么写，后面继续。
