29 strings / 1018 words

Translation Source string Target string
Boost Beast Translation (zh_Hans)/Doc / Qbk / 03 Core / 3 Timeouts (qbk) — English
Timeouts __example__
Timeouts __example__
Boost Beast Translation (zh_Hans)/Doc / Qbk / 03 Core / 3 Timeouts (qbk) — English
Network programs must handle adverse connection conditions; the most common is that a connected peer goes offline unexpectedly. Protocols have no way of identifying this reliably: the peer is offline after all, and unable to send a message announcing the absence. A peer can go offline for various reasons:
Network programs must handle adverse connection conditions; the most common is that a connected peer goes offline unexpectedly. Protocols have no way of identifying this reliably: the peer is offline after all, and unable to send a message announcing the absence. A peer can go offline for various reasons:
Boost Beast Translation (zh_Hans)/Doc / Qbk / 03 Core / 3 Timeouts (qbk) — English
To determine when a peer is offline or idle, a program will implement a [@https://en.wikipedia.org/wiki/Timeout_(computing) timeout] algorithm, which closes the connection after a specified amount of time if some condition is met. For example, if no data is received for the duration. A timeout may be used to:
To determine when a peer is offline or idle, a program will implement a [@https://en.wikipedia.org/wiki/Timeout_(computing) timeout] algorithm, which closes the connection after a specified amount of time if some condition is met. For example, if no data is received for the duration. A timeout may be used to:
Boost Beast Translation (zh_Hans)/Doc / Qbk / 03 Core / 3 Timeouts (qbk) — English
Traditionally, programs use a [@boost:/doc/html/boost_asio/reference/steady_timer.html `net::steady_timer`] to determine when a timeout occurs, and then call [@boost:/doc/html/boost_asio/reference/basic_socket/close/overload2.html `close`] on the socket to release the resources. The complexity of managing a separate timer is often a source of [@http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2018/p1269r0.html#timers frustration] for non-experts.
Traditionally, programs use a [@boost:/doc/html/boost_asio/reference/steady_timer.html `net::steady_timer`] to determine when a timeout occurs, and then call [@boost:/doc/html/boost_asio/reference/basic_socket/close/overload2.html `close`] on the socket to release the resources. The complexity of managing a separate timer is often a source of [@http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2018/p1269r0.html#timers frustration] for non-experts.
Boost Beast Translation (zh_Hans)/Doc / Qbk / 03 Core / 3 Timeouts (qbk) — English
For portability reasons, networking does not provide timeouts
For portability reasons, networking does not provide timeouts
Boost Beast Translation (zh_Hans)/Doc / Qbk / 03 Core / 3 Timeouts (qbk) — English
To simplify the handling of timeouts, these provided types wrap a [@boost:/doc/html/boost_asio/reference/basic_stream_socket.html `net::basic_stream_socket`] to provide additional features:
To simplify the handling of timeouts, these provided types wrap a [@boost:/doc/html/boost_asio/reference/basic_stream_socket.html `net::basic_stream_socket`] to provide additional features:
Boost Beast Translation (zh_Hans)/Doc / Qbk / 03 Core / 3 Timeouts (qbk) — English
[link beast.ref.boost__beast__tcp_stream `tcp_stream`]
[link beast.ref.boost__beast__tcp_stream `tcp_stream`]
Boost Beast Translation (zh_Hans)/Doc / Qbk / 03 Core / 3 Timeouts (qbk) — English
[itemized_list [Timeouts for logical operations] [[@boost:/doc/html/boost_asio/reference/ip__tcp.html `net::ip::tcp`] protocol] [[@boost:/doc/html/boost_asio/reference/executor.html `net::executor`] executor] [[link beast.ref.boost__beast__unlimited_rate_policy `unlimited_rate_policy`] rate limits] ]
[itemized_list [Timeouts for logical operations] [[@boost:/doc/html/boost_asio/reference/ip__tcp.html `net::ip::tcp`] protocol] [[@boost:/doc/html/boost_asio/reference/executor.html `net::executor`] executor] [[link beast.ref.boost__beast__unlimited_rate_policy `unlimited_rate_policy`] rate limits] ]
Boost Beast Translation (zh_Hans)/Doc / Qbk / 03 Core / 3 Timeouts (qbk) — English
[link beast.ref.boost__beast__basic_stream `basic_stream`]
[link beast.ref.boost__beast__basic_stream `basic_stream`]
Boost Beast Translation (zh_Hans)/Doc / Qbk / 03 Core / 3 Timeouts (qbk) — English
[itemized_list [Timeouts for logical operations] [Configurable __Protocol__ type] [Configurable __Executor__ type] [Configurable __RatePolicy__ type] ]
[itemized_list [Timeouts for logical operations] [Configurable __Protocol__ type] [Configurable __Executor__ type] [Configurable __RatePolicy__ type] ]
Boost Beast Translation (zh_Hans)/Doc / Qbk / 03 Core / 3 Timeouts (qbk) — English
Construction
Construction
Boost Beast Translation (zh_Hans)/Doc / Qbk / 03 Core / 3 Timeouts (qbk) — English
The `tcp_stream` is designed as a replacement for [@boost:/doc/html/boost_asio/reference/ip__tcp/socket.html `net::ip::tcp::socket`]. Any program which currently uses a socket, can switch to a `tcp_stream` and achieve the features above (although some interfaces are different, see below). Networking now allows I/O objects to construct with any instance of __ExecutionContext__ or __Executor__ objects. Here we construct a stream which uses a particular I/O context to dispatch completion handlers:
The `tcp_stream` is designed as a replacement for [@boost:/doc/html/boost_asio/reference/ip__tcp/socket.html `net::ip::tcp::socket`]. Any program which currently uses a socket, can switch to a `tcp_stream` and achieve the features above (although some interfaces are different, see below). Networking now allows I/O objects to construct with any instance of __ExecutionContext__ or __Executor__ objects. Here we construct a stream which uses a particular I/O context to dispatch completion handlers:
Boost Beast Translation (zh_Hans)/Doc / Qbk / 03 Core / 3 Timeouts (qbk) — English
Alternatively, we can construct the stream from an executor:
Alternatively, we can construct the stream from an executor:
Boost Beast Translation (zh_Hans)/Doc / Qbk / 03 Core / 3 Timeouts (qbk) — English
The function [@boost:/doc/html/boost_asio/reference/make_strand.html `make_strand`] returns a strand constructed from an execution context or executor. When a [@boost:/doc/html/boost_asio/reference/strand.html `net::strand`] is chosen for the stream's executor, all completion handlers which do not already have an associated executor will use the strand. This is both a notational convenience (no need for `strand::wrap` or `bind_executor` at call sites) and a measure of safety, as it is no longer possible to forget to use the strand.
The function [@boost:/doc/html/boost_asio/reference/make_strand.html `make_strand`] returns a strand constructed from an execution context or executor. When a [@boost:/doc/html/boost_asio/reference/strand.html `net::strand`] is chosen for the stream's executor, all completion handlers which do not already have an associated executor will use the strand. This is both a notational convenience (no need for `strand::wrap` or `bind_executor` at call sites) and a measure of safety, as it is no longer possible to forget to use the strand.
Boost Beast Translation (zh_Hans)/Doc / Qbk / 03 Core / 3 Timeouts (qbk) — English
Connecting
Connecting
Boost Beast Translation (zh_Hans)/Doc / Qbk / 03 Core / 3 Timeouts (qbk) — English
Before data can be exchanged, the stream needs to be connected to a peer. The following code sets a timeout for an asynchronous connect operation. In Beast, functions to connect to a range of endpoints (such as the range returned by [@boost:/doc/html/boost_asio/reference/ip__basic_resolver/resolve/overload3.html `net::ip::tcp::resolver::resolve`]) are members of the class rather than free functions such as [@boost:/doc/html/boost_asio/reference/async_connect.html `net::async_connect`].
Before data can be exchanged, the stream needs to be connected to a peer. The following code sets a timeout for an asynchronous connect operation. In Beast, functions to connect to a range of endpoints (such as the range returned by [@boost:/doc/html/boost_asio/reference/ip__basic_resolver/resolve/overload3.html `net::ip::tcp::resolver::resolve`]) are members of the class rather than free functions such as [@boost:/doc/html/boost_asio/reference/async_connect.html `net::async_connect`].
Boost Beast Translation (zh_Hans)/Doc / Qbk / 03 Core / 3 Timeouts (qbk) — English
A server will use an acceptor bound to a particular IP address and port to listen to and receive incoming connection requests. The acceptor returns an ordinary socket. A `tcp_stream` can be move-constructed from the underlying `basic_stream_socket` thusly:
A server will use an acceptor bound to a particular IP address and port to listen to and receive incoming connection requests. The acceptor returns an ordinary socket. A `tcp_stream` can be move-constructed from the underlying `basic_stream_socket` thusly:
Boost Beast Translation (zh_Hans)/Doc / Qbk / 03 Core / 3 Timeouts (qbk) — English
Reading and Writing
Reading and Writing
Boost Beast Translation (zh_Hans)/Doc / Qbk / 03 Core / 3 Timeouts (qbk) — English
Timeouts apply to the logical operation, expressed as a series of asynchronous calls, rather than just the next call. This code reads a line from the stream and writes it back. Both the read and the write must complete within 30 seconds from when the timeout was set; the timer is not reset between operations.
Timeouts apply to the logical operation, expressed as a series of asynchronous calls, rather than just the next call. This code reads a line from the stream and writes it back. Both the read and the write must complete within 30 seconds from when the timeout was set; the timer is not reset between operations.
Boost Beast Translation (zh_Hans)/Doc / Qbk / 03 Core / 3 Timeouts (qbk) — English
Since reads and writes can take place concurrently, it is possible to have two simultaneous logical operations where each operation either only reads, or only writes. The beginning of a new read or write operation will use the most recently set timeout. This will not affect operations that are already outstanding.
Since reads and writes can take place concurrently, it is possible to have two simultaneous logical operations where each operation either only reads, or only writes. The beginning of a new read or write operation will use the most recently set timeout. This will not affect operations that are already outstanding.
Boost Beast Translation (zh_Hans)/Doc / Qbk / 03 Core / 3 Timeouts (qbk) — English
When a timeout is set, it cancels any previous read or write timeout for which no outstanding operation is in progress. Algorithms which loop over logical operations simply need to set the timeout once before the logical operation, it is not necessary to call `expires_never` in this case. Here we implement an algorithm which continuously echoes lines back, with a timeout. This example is implemented as a complete function.
When a timeout is set, it cancels any previous read or write timeout for which no outstanding operation is in progress. Algorithms which loop over logical operations simply need to set the timeout once before the logical operation, it is not necessary to call `expires_never` in this case. Here we implement an algorithm which continuously echoes lines back, with a timeout. This example is implemented as a complete function.
Boost Beast Translation (zh_Hans)/Doc / Qbk / 03 Core / 3 Timeouts (qbk) — English
https_get
https_get
Boost Beast Translation (zh_Hans)/Doc / Qbk / 03 Core / 3 Timeouts (qbk) — English
It is important to note that all of the examples thus far which perform reads and writes with a timeout, make use of the existing networking stream algorithms. As these algorithms are written generically to work with any object meeting the stream requirements, they transparently support timeouts when used with `tcp_stream`. This can be used to enable timeouts for stream wrappers that do not currently support timeouts.
It is important to note that all of the examples thus far which perform reads and writes with a timeout, make use of the existing networking stream algorithms. As these algorithms are written generically to work with any object meeting the stream requirements, they transparently support timeouts when used with `tcp_stream`. This can be used to enable timeouts for stream wrappers that do not currently support timeouts.
Boost Beast Translation (zh_Hans)/Doc / Qbk / 03 Core / 3 Timeouts (qbk) — English
The following code establishes an encrypted connection, writes an HTTP request, reads the HTTP response, and closes the connection gracefully. If these operations take longer than 30 seconds total, a timeout occurs. This code is intended to show how `tcp_stream` can be used to enable timeouts across unmodified stream algorithms which were not originally written to support timing out, and how a blocking algorithm may be written from asynchronous intermediate operations.
The following code establishes an encrypted connection, writes an HTTP request, reads the HTTP response, and closes the connection gracefully. If these operations take longer than 30 seconds total, a timeout occurs. This code is intended to show how `tcp_stream` can be used to enable timeouts across unmodified stream algorithms which were not originally written to support timing out, and how a blocking algorithm may be written from asynchronous intermediate operations.
Boost Beast Translation (zh_Hans)/Doc / Qbk / 03 Core / 3 Timeouts (qbk) — English
Rate Limiting __example__
Rate Limiting __example__
Boost Beast Translation (zh_Hans)/Doc / Qbk / 03 Core / 3 Timeouts (qbk) — English
The [link beast.ref.boost__beast__basic_stream `basic_stream`] class template supports an additional `RatePolicy` template parameter. Objects of this type must meet the requirements of __RatePolicy__. They are used to implement rate limiting or bandwidth management. The default policy for `basic_stream` and `tcp_stream` is [link beast.ref.boost__beast__unlimited_rate_policy `unlimited_rate_policy`], which places no limits on reading and writing. The library comes with the [link beast.ref.boost__beast__simple_rate_policy `simple_rate_policy`], allowing for independent control of read and write limits expressed in terms of bytes per second. The follow code creates an instance of the basic stream with a simple rate policy, and sets the read and write limits:
The [link beast.ref.boost__beast__basic_stream `basic_stream`] class template supports an additional `RatePolicy` template parameter. Objects of this type must meet the requirements of __RatePolicy__. They are used to implement rate limiting or bandwidth management. The default policy for `basic_stream` and `tcp_stream` is [link beast.ref.boost__beast__unlimited_rate_policy `unlimited_rate_policy`], which places no limits on reading and writing. The library comes with the [link beast.ref.boost__beast__simple_rate_policy `simple_rate_policy`], allowing for independent control of read and write limits expressed in terms of bytes per second. The follow code creates an instance of the basic stream with a simple rate policy, and sets the read and write limits:
Boost Beast Translation (zh_Hans)/Doc / Qbk / 03 Core / 3 Timeouts (qbk) — English
More sophisticated rate policies can be implemented as user-defined types which meet the requirements of __RatePolicy__. Here, we develop a rate policy that measures the instantaneous throughput of reads and writes. First we write a small utility class that applies an exponential smoothing function to a series of discrete rate samples, to calculate instantaneous throughput.
More sophisticated rate policies can be implemented as user-defined types which meet the requirements of __RatePolicy__. Here, we develop a rate policy that measures the instantaneous throughput of reads and writes. First we write a small utility class that applies an exponential smoothing function to a series of discrete rate samples, to calculate instantaneous throughput.
Boost Beast Translation (zh_Hans)/Doc / Qbk / 03 Core / 3 Timeouts (qbk) — English
Then we define our rate policy object. We friend the type [link beast.ref.boost__beast__rate_policy_access `rate_policy_access`] to allow our implementation to be private, but still allow the `basic_stream` access to call the required functions. This lets us avoid having to write a cumbersome friend declaration for the `basic_stream` class template. Public members of rate policy objects become part of the stream object's interface, through a call to `rate_policy`.
Then we define our rate policy object. We friend the type [link beast.ref.boost__beast__rate_policy_access `rate_policy_access`] to allow our implementation to be private, but still allow the `basic_stream` access to call the required functions. This lets us avoid having to write a cumbersome friend declaration for the `basic_stream` class template. Public members of rate policy objects become part of the stream object's interface, through a call to `rate_policy`.
Boost Beast Translation (zh_Hans)/Doc / Qbk / 03 Core / 3 Timeouts (qbk) — English
To use our new policy we declare an instance of the stream, and then use it with stream algorithms as usual. At any time, we can determine the current read or write rates by calling into the policy.
To use our new policy we declare an instance of the stream, and then use it with stream algorithms as usual. At any time, we can determine the current read or write rates by calling into the policy.