Context原理及其适用场景 随手记 李帅(飞雪无情) n 常见并发模式 n Context实现原理 n TLS VS Context n 典型适用场景 大纲 Channel Fan-in func fanIn(sum1, sum2 <-chan int) <-chan int { sum := make(chan int) go func() { for {sum <- <-sum1} } } Context l 一个任务，需要多个goroutine完成 l 一个请求，会触发好多个goroutine做不同的事情 l 如果我们的任务终止了，请求取消了，这些正在运行 的goroutine怎么办？ l 使用Context来简化这些操作 Context能做什么 u 手动、定时、超时发出取消信号 u 跨API传值 u 控制生成Context树结构（Context链） Context main() { rootCtx := context.Background() ctx, cancel := context.WithCancel(rootCtx) go watch(ctx) go watch(ctx) time.Sleep(1 * time.Second) cancel() } func watch(ctx context.Context) { for { select {

parse, it also dispatches to the appropriate code. • Click has a strong concept of an invocation context that allows subcommands to respond to data from the parent command. • Click has strong information Declares a parameter to be a file for reading or writing. The file is automatically closed once the context tears down (after the command finished working). Files can be opened for reading or writing. The implement a custom type, you need to subclass the ParamType class. Types can be invoked with or without context and parameter object, which is why they need to be able to deal with this. The following code implements

parse, it also dispatches to the appropriate code. • Click has a strong concept of an invocation context that allows subcommands to respond to data from the parent command. • Click has strong information Declares a parameter to be a file for reading or writing. The file is automatically closed once the context tears down (after the command finished working). Files can be opened for reading or writing. The implement a custom type, you need to subclass the ParamType class. Types can be invoked with or without context and parameter object, which is why they need to be able to deal with this. The following code implements

parse, it also dispatches to the appropriate code. • Click has a strong concept of an invocation context that allows subcommands to respond to data from the parent command. • Click has strong information Declares a parameter to be a file for reading or writing. The file is automatically closed once the context tears down (after the command finished working). Files can be opened for reading or writing. The implement a custom type, you need to subclass the ParamType class. Types can be invoked with or without context and parameter object, which is why they need to be able to deal with this. The following code implements

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 3.2.1. Context Management and Caching . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46 Context Loaders. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54 3.5.6. Context Management. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54 Context Configuration with XML resources

Production Keep Developing! Templates Jinja Setup Standard Context Standard Filters Controlling Autoescaping Registering Filters Context Processors Testing Flask Applications The Application The Testing Test Logging In and Out Test Adding Messages Other Testing Tricks Faking Resources and Context Keeping the Context Around Accessing and Modifying Sessions Testing JSON APIs Testing CLI Commands Application Request Context Decorator Based Signal Subscriptions Core Signals Pluggable Views Basic Principle Method Hints Method Based Dispatching Decorating Views Method Views for APIs The Application Context Purpose

. . . . . . . . 86 1.14 The Application Context . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89 1.15 The Request Context . . . . . . . . . . . . . . . . . . . . a request in order to stay threadsafe. This approach is convenient, but requires a valid request context for dependency injection or when attempting to reuse code which uses a value pegged to the request use the test_request_context() method to try out url_for(). test_request_context() tells Flask to behave as though it’s handling a request even while we use a Python shell. See Context Locals. from flask

parse, it also dispatches to the appropriate code. • Click has a strong concept of an invocation context that allows subcommands to respond to data from the parent command. • Click has strong information Declares a parameter to be a file for reading or writing. The file is automatically closed once the context tears down (after the command finished working). Files can be opened for reading or writing. The implement a custom type, you need to subclass the ParamType class. Types can be invoked with or without context and parameter object, which is why they need to be able to deal with this. The following code implements

parse, it also dispatches to the appropriate code. • Click has a strong concept of an invocation context that allows subcommands to respond to data from the parent command. • Click has strong information Declares a parameter to be a file for reading or writing. The file is automatically closed once the context tears down (after the command finished working). Files can be opened for reading or writing. The implement a custom type, you need to subclass the ParamType class. Types can be invoked with or without context and parameter object, which is why they need to be able to deal with this. The following code implements

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 2.5 Cloning the context . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 2.6 Coding main(int argc, char **argv) { char *input; float zoom, rotate; int page_number, page_count; fz_context *ctx; fz_document *doc; (continues on next page) 5 MuPDF Documentation, Release 1.21.2 (continued 0; /* Create a context to hold the exception stack and various caches. */ ctx = fz_new_context(NULL, NULL, FZ_STORE_UNLIMITED); if (!ctx) { fprintf(stderr, "cannot create mupdf context\n"); return EXIT_FAILURE;