work queue to be empty. workers = gen.multi([worker() for _ in range(concurrency)]) await q.join(timeout=timedelta(seconds=300)) assert fetching == (fetched | dead) print("Done in %d seconds, fetched %s default_type application/octet-stream; access_log /var/log/nginx/access.log; keepalive_timeout 65; proxy_read_timeout 200; sendfile on; tcp_nopush on; tcp_nodelay on; gzip on; gzip_min_length 1000; gzip_proxied application/xml application/atom+xml text/javascript; # Only retry if there was a communication error, not a timeout # on the Tornado server (to avoid propagating "queries of death" # to all frontends) proxy_next_upstream

queue to be empty. workers = gen.multi([worker() for _ in range(concurrency)]) await q.join(timeout=timedelta(seconds=300)) assert fetching == (fetched | dead) print("Done in %d seconds, fetched default_type application/octet-stream;access_log /var/log/nginx/access.log; keepalive_timeout 65; proxy_read_timeout 200; sendfile on; tcp_nopush on; tcp_nodelay on; gzip on; gzip_min_length application/atom+xml text/javascript; # Only retry if there was a communication error, not a timeout # on the Tornado server (to avoid propagating "queries of death" # to all frontends)

CPU_THREADS, the number of logical CPU cores available. JULIA_WORKER_TIMEOUT A Float64 that sets the value of Distributed.worker_timeout() (default: 60.0). This function gives the number of seconds a worker whether a timer is still active. Use t.timeout and t.interval to read the setup conditions of a Timer t. julia> t = Timer(1.0; interval=0.5) Timer (open, timeout: 1.0 s, interval: 0.5 s) @0x000000010f4e6e90 @0x000000010f4e6e90 julia> isopen(t) true julia> t.timeout 1.0 julia> close(t) julia> isopen(t) false Note interval is subject to accumulating time skew. If you need precise events at a particular abso-

CPU_THREADS, the number of logical CPU cores available. JULIA_WORKER_TIMEOUT A Float64 that sets the value of Distributed.worker_timeout() (default: 60.0). This function gives the number of seconds a worker whether a timer is still active. Use t.timeout and t.interval to read the setup conditions of a Timer t. julia> t = Timer(1.0; interval=0.5) Timer (open, timeout: 1.0 s, interval: 0.5 s) @0x000000010f4e6e90 @0x000000010f4e6e90 julia> isopen(t) true julia> t.timeout 1.0 julia> close(t) julia> isopen(t) false Note interval is subject to accumulating time skew. If you need precise events at a particular abso-

CPU_THREADS, the number of logical CPU cores available. JULIA_WORKER_TIMEOUT A Float64 that sets the value of Distributed.worker_timeout() (default: 60.0). This function gives the number of seconds a worker whether a timer is still active. Use t.timeout and t.interval to read the setup conditions of a Timer t. julia> t = Timer(1.0; interval=0.5) Timer (open, timeout: 1.0 s, interval: 0.5 s) @0x000000010f4e6e90 @0x000000010f4e6e90 julia> isopen(t) true julia> t.timeout 1.0 julia> close(t) julia> isopen(t) false Note interval is subject to accumulating time skew. If you need precise events at a particular abso-

CPU_THREADS, the number of logical CPU cores available. JULIA_WORKER_TIMEOUT A Float64 that sets the value of Distributed.worker_timeout() (default: 60.0). This function gives the number of seconds a worker whether a timer is still active. Use t.timeout and t.interval to read the setup conditions of a Timer t. julia> t = Timer(1.0; interval=0.5) Timer (open, timeout: 1.0 s, interval: 0.5 s) @0x000000010f4e6e90 @0x000000010f4e6e90 julia> isopen(t) true julia> t.timeout 1.0 julia> close(t) julia> isopen(t) false Note interval is subject to accumulating time skew. If you need precise events at a particular abso-

CPU_THREADS, the number of logical CPU cores available. JULIA_WORKER_TIMEOUT A Float64 that sets the value of Distributed.worker_timeout() (default: 60.0). This function gives the number of seconds a worker whether a timer is still active. Use t.timeout and t.interval to read the setup conditions of a Timer t. julia> t = Timer(1.0; interval=0.5) Timer (open, timeout: 1.0 s, interval: 0.5 s) @0x000000010f4e6e90 @0x000000010f4e6e90 julia> isopen(t) true julia> t.timeout 1.0 julia> close(t) julia> isopen(t) false Note interval is subject to accumulating time skew. If you need precise events at a particular abso-

CPU_THREADS, the number of logical CPU cores available. JULIA_WORKER_TIMEOUT A Float64 that sets the value of Distributed.worker_timeout() (default: 60.0). This function gives the number of seconds a worker Timer requires yield points to update its state. For instance, isopen(t::Timer) cannot be used to timeout a non-yielding while loop. sourceCHAPTER 41. ESSENTIALS 620 Base.AsyncCondition – Type. AsyncCondition() Return x. source Base.timedwait – Function. timedwait(testcb, timeout::Real; pollint::Real=0.1) Waits until testcb() returns true or timeout seconds have passed, whichever is earlier. The test function

CPU_THREADS, the number of logical CPU cores available. JULIA_WORKER_TIMEOUT A Float64 that sets the value of Distributed.worker_timeout() (default: 60.0). This function gives the number of seconds a worker Timer requires yield points to update its state. For instance, isopen(t::Timer) cannot be used to timeout a non-yielding while loop. sourceCHAPTER 41. ESSENTIALS 620 Base.AsyncCondition – Type. AsyncCondition() Return x. source Base.timedwait – Function. timedwait(testcb, timeout::Real; pollint::Real=0.1) Waits until testcb() returns true or timeout seconds have passed, whichever is earlier. The test function

构建我们自己的异步抽象 我们也可以将 futures 组合起来形成一个新模式。例如，我们可以使用已有的异步代码块构建 一个 timeout 函数。当我们完成时，其结果将是另一个可以用来构建进一步异步抽象的代码 块。 示例 17-27 展示了我们预期 timeout 如何处理一个缓慢运行的 future。 文件名：src/main.rs let slow = async { trpl::sleep(Duration::from_millis(100)).await; "I finished!" }; match timeout(slow, Duration::from_millis(10)).await { Ok(message) => println!("Succeeded with '{message}'") println!("Failed after {} seconds", duration.as_secs()) } } 让我们来实现它！首先，让我们考虑一下 timeout 的 API： • 它需要是一个 async 函数以便可以 await。 • 它的第一个参数应该是需要运行的 future。我们可以使用泛型以便可以处理任意 future。 • 它的第二个参数将是需要等待的最大时间。如果我们使用