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13 string ID 146
	Source string description type: heading

	English Synchronous I/O 15/10000 · 15
14 string ID 148
	Source string description type: paragraph

	English Synchronous input and output is accomplished through blocking function calls that return with the result of the operation. Such operations typically cannot be canceled and do not have a method for setting a timeout. The __SyncReadStream__ and __SyncWriteStream__ concepts define requirements for ['synchronous streams]: a portable I/O abstraction that transfers data using buffer sequences to represent bytes and either `error_code` or an exception to report any failures. [@boost:/doc/html/boost_asio/reference/basic_stream_socket.html ['net::basic_stream_socket]] is a synchronous stream commonly used to form TCP/IP connections. User-defined types which meet the requirements are possible: 692/10000 · 692
15 string ID 162
	Source string description type: paragraph

	English A ['synchronous stream algorithm] is written as a function template accepting a stream object meeting the named requirements for synchronous reading, writing, or both. This example shows an algorithm which writes text and uses exceptions to indicate errors: 257/10000 · 257
16 string ID 170
	Source string description type: paragraph

	English The same algorithm may be expressed using error codes instead of exceptions: 76/10000 · 76
17 string ID 176
	Source string description type: heading

	English Asynchronous I/O 16/10000 · 16
18 string ID 178
	Source string description type: paragraph

	English An asynchronous operation begins with a call to an [@boost:/doc/html/boost_asio/reference/asynchronous_operations.html ['initiating function]], which starts the operation and returns to the caller immediately. This ['outstanding] asynchronous operation proceeds concurrently without blocking the caller. When the externally observable side effects are fully established, a movable function object known as a [@boost:/doc/html/boost_asio/reference/CompletionHandler.html ['completion handler]] provided in the initiating function call is queued for execution with the results, which may include the error code and other specific information. An asynchronous operation is said to be ['completed] after the completion handler is queued. The code that follows shows how some text may be written to a socket asynchronously, invoking a lambda when the operation is complete: 868/10000 · 868
19 string ID 196
	Source string description type: paragraph

	English Every completion handler (also referred to as a [@https://en.wikipedia.org/wiki/Continuation ['continuation]]) has both an [@boost:/doc/html/boost_asio/overview/core/allocation.html ['associated allocator]] returned by [@boost:/doc/html/boost_asio/reference/get_associated_allocator.html `net::get_associated_allocator`], , an [@boost:/doc/html/boost_asio/reference/associated_cancellation_slot.html ['associated cancellation slot]] returned by [@boost:/doc/html/boost_asio/reference/associated_cancellation_slot.html `net::get_associated_cancellation_slot`]. and an [@boost:/doc/html/boost_asio/reference/associated_executor.html ['associated executor]] returned by [@boost:/doc/html/boost_asio/reference/get_associated_executor.html `net::get_associated_executor`]. These associations may be specified intrusively: 816/10000 · 816
20 string ID 214
	Source string description type: paragraph

	English Or these associations may be specified non-intrusively, by specializing the class templates [@boost:/doc/html/boost_asio/reference/associated_allocator.html `net::associated_allocator`] , [@boost:/doc/html/boost_asio/reference/associated_cancellation_slot.html `net::associated_cancellation_slot`] and [@boost:/doc/html/boost_asio/reference/associated_executor.html `net::associated_executor`]: 394/10000 · 394
21 string ID 224
	Source string description type: paragraph

	English The function [@boost:/doc/html/boost_asio/reference/bind_executor.html `net::bind_executor`] may be used when the caller wants to change the executor of a completion handler. 174/10000 · 174
22 string ID 229
	Source string description type: paragraph

	English The allocator is used by the implementation to obtain any temporary storage necessary to perform the operation. Temporary allocations are always freed before the completion handler is invoked. The executor is a cheaply copyable object providing the algorithm used to invoke the completion handler. Unless customized by the caller, a completion handler defaults to using `std::allocator<void>` and the executor of the corresponding I/O object. 442/10000 · 442
23 string ID 236
	Source string description type: paragraph

	English The function [@boost:/doc/html/boost_asio/reference/bind_allocator.html `net::bind_allocator`] can be used when the caller wants to assign a custom allocator to the operation. 175/10000 · 175
24 string ID 241
	Source string description type: paragraph

	English A completion token's associated cancellation_slot can be used to cancel single operations. This is often passed through by the completion token such as [@boost:/doc/html/boost_asio/reference/use_awaitable.html `net::use_awaitable`] or [@boost:/doc/html/boost_asio/reference/yield_context.html `net::yield_context`] . 316/10000 · 316
25 string ID 248
	Source string description type: paragraph

	English The available [@boost:/doc/html/boost_asio/reference/cancellation_type.html cancellation types] are listed below. 113/10000 · 113
26 string ID 250
	Source string description type: list

	English # `terminal` 12/10000 · 12
27 string ID 254
	Source string description type: list

	English # `partial` 11/10000 · 11
28 string ID 259
	Source string description type: list

	English # `total` 9/10000 · 9
29 string ID 266
	Source string description type: paragraph

	English Networking prescribes facilities to determine the context in which handlers run. Every I/O object refers to an __ExecutionContext__ for obtaining the __Executor__ instance used to invoke completion handlers. An executor determines where and how completion handlers are invoked. Executors obtained from an instance of __io_context__ offer a basic guarantee: handlers will only be invoked from threads which are currently calling [@boost:/doc/html/boost_asio/reference/io_context/run/overload1.html `net::io_context::run`]. 521/10000 · 521
30 string ID 274
	Source string description type: paragraph

	English The __AsyncReadStream__ and __AsyncWriteStream__ concepts define requirements for ['asynchronous streams]: a portable I/O abstraction that exchanges data asynchronously using buffer sequences to represent bytes and `error_code` to report any failures. An ['asynchronous stream algorithm] is written as a templated initiating function template accepting a stream object meeting the named requirements for asynchronous reading, writing, or both. This example shows an algorithm which writes some text to an asynchronous stream: 525/10000 · 525
31 string ID 288
	Source string description type: heading

	English Concurrency 11/10000 · 11
32 string ID 290
	Source string description type: paragraph

	English I/O objects such as sockets and streams [*are not thread-safe]. Although it is possible to have more than one operation outstanding (for example, a simultaneous asynchronous read and asynchronous write) the stream object itself may only be accessed from one thread at a time. This means that member functions such as move constructors, destructors, or initiating functions must not be called concurrently. Usually this is accomplished with synchronization primitives such as a [@https://en.cppreference.com/w/cpp/thread/mutex `mutex`], but concurrent network programs need a better way to access shared resources, since acquiring ownership of a mutex could block threads from performing uncontended work. For efficiency, networking adopts a model of using threads without explicit locking by requiring all access to I/O objects to be performed within a [@boost:/doc/html/boost_asio/overview/core/strands.html ['strand]]. 920/10000 · 920

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