SQLITE源码剖析(8)

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　　声明：本SQLite源码剖析系列为刘兴(http://deepfuture.iyunv.com/)原创，未经笔者授权，任何人和机构不能转载
　　/*库线程安全
　　** CAPI3REF: Test To See If The Library Is Threadsafe
　　**SQLITE_THREADSAFE预处理宏编译时选项设为0,则忽略SQLITE的互斥代码，
　　**此时，sqlite3_threadsafe()返回0
　　** ^The sqlite3_threadsafe() function returns zero if and only if
　　** SQLite was compiled mutexing code omitted due to the
　　** [SQLITE_THREADSAFE] compile-time option being set to 0.
　　**SQLITE可在有互斥和没有互斥情况下编译，当SQLITE_THREADSAFE宏是1或2**时，互斥被允许，SQLITE是线程安全的。该宏为0时，不使用互斥，超过一
　　**个线程同时使用SQLite是不安全的
　　** SQLite can be compiled with or without mutexes.  When
　　** the [SQLITE_THREADSAFE] C preprocessor macro is 1 or 2, mutexes
　　** are enabled and SQLite is threadsafe.  When the
　　** [SQLITE_THREADSAFE] macro is 0, 
　　** the mutexes are omitted.  Without the mutexes, it is not safe
　　** to use SQLite concurrently from more than one thread.
　　**允许互斥，将会产生一些可预见的后果。如果速度是第一位的，最好是禁止
　　**互斥，对于最好安全性而言，互斥要开启，默认的行为是互斥开启。
　　** Enabling mutexes incurs a measurable performance penalty.
　　** So if speed is of utmost importance, it makes sense to disable
　　** the mutexes.  But for maximum safety, mutexes should be enabled.
　　** ^The default behavior is for mutexes to be enabled.
　　**这些接口被应用程序使用，确认该SQLITE版本编译链接时是否使用
　　**sqlite_threadsafe宏
　　** This interface can be used by an application to make sure that the
　　** version of SQLite that it is linking against was compiled with
　　** the desired setting of the [SQLITE_THREADSAFE] macro.
　　**该接口仅在编译时，互斥设置了SQLITE_THREADSAFE标志时才报告，如
　　**果 SQLITE使用SQLITE_THREADSAFE=1或=2的方式编译，互斥被允许，但
　　**通过SQLITE_CONFIG_SINGLETHREAD、SQLITE_CONFIG_MULTITHREAD能部分或
　　**完全禁止对sqlite3_config()的调用，
　　** This interface only reports on the compile-time mutex setting
　　** of the [SQLITE_THREADSAFE] flag.  If SQLite is compiled with
　　** SQLITE_THREADSAFE=1 or =2 then mutexes are enabled by default but
　　** can be fully or partially disabled using a call to [sqlite3_config()]
　　** with the verbs [SQLITE_CONFIG_SINGLETHREAD], [SQLITE_CONFIG_MULTITHREAD],
　　** or [SQLITE_CONFIG_MUTEX].  
　　**sqlite3_threadsafe()函数的返回值仅指示编译时设置了线程安全
　　**不能被sqlite3_config()可在运行时改变
　　**^(The return value of the
　　** sqlite3_threadsafe() function shows only the compile-time setting of
　　** thread safety, not any run-time changes to that setting made by
　　** sqlite3_config(). In other words, the return value from sqlite3_threadsafe()
　　** is unchanged by calls to sqlite3_config().)^
　　**调用sqlite3_config()不能改变sqlite3_threadsafe()返回值，
　　** See the [threading mode] documentation for additional information.
　　*/
　　SQLITE_API int sqlite3_threadsafe(void);
　　/*数据库连接句柄
　　** CAPI3REF: Database Connection Handle
　　** KEYWORDS: {database connection} {database connections}
　　**关键字：{database connection} {database connections}
　　**每个打开的SQLite数据库做为一个指针出现，该指针指向隐藏的sqlite3
　　**结构的实例，建议将sqlite3指针视 为对象 ，
　　**sqlite3_open()、sqlite3_open16()、sqlite3_open_v2()接口是这该对象
　　**的构造器，sqlite3_close()是析构器。
　　** Each open SQLite database is represented by a pointer to an instance of
　　** the opaque structure named "sqlite3".  It is useful to think of an sqlite3
　　** pointer as an object.  The [sqlite3_open()], [sqlite3_open16()], and
　　** [sqlite3_open_v2()] interfaces are its constructors, and [sqlite3_close()]
　　** is its destructor.  
　　**还有一些其它接口sqlite3_prepare_v2()、sqlite3_create_function()、
　　**sqlite3_busy_timeout()为sqlite3 对象 的方法 
　　There are many other interfaces (such as
　　** [sqlite3_prepare_v2()], [sqlite3_create_function()], and
　　** [sqlite3_busy_timeout()] to name but three) that are methods on an
　　** sqlite3 object.
　　*/
　　typedef struct sqlite3 sqlite3;