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First, the async keyword indicates to C# that the method is asynchronous, meaning that it may use an arbitrary number of await expressions and will bind the result to a promise. [1]: 165–168 The return type, Task<T>, is C#'s analogue to the concept of a promise, and here is indicated to have a result value of type int.
408 Request Timeout The server timed out waiting for the request. According to HTTP specifications: "The client did not produce a request within the time that the server was prepared to wait. The client MAY repeat the request without modifications at any later time." 409 Conflict
In computer operating systems, a process (or task) may wait for another process to complete its execution. In most systems, a parent process can create an independently executing child process . The parent process may then issue a wait system call , which suspends the execution of the parent process while the child executes.
Busy-waiting itself can be made much less wasteful by using a delay function (e.g., sleep()) found in most operating systems. This puts a thread to sleep for a specified time, during which the thread will waste no CPU time. If the loop is checking something simple then it will spend most of its time asleep and will waste very little CPU time.
A timeout can also be specified on the wait using the wait_for() or wait_until() member functions to avoid indefinite blocking. If the future arose from a call to std::async then a blocking wait (without a timeout) may cause synchronous invocation of the function to compute the result on the waiting thread.
This was a spurious wakeup, some other thread occurred // first and caused the condition to become false again, and we must // wait again. wait (m, cv); // Temporarily prevent any other thread on any core from doing // operations on m or cv. // release(m) // Atomically release lock "m" so other // // code using this concurrent data // // can ...
408 Request Timeout Couldn't find the user in time. The server could not produce a response within a suitable amount of time, for example, if it could not determine the location of the user in time. The client MAY repeat the request without modifications at any later time. [1]: §21.4.9 409 Conflict User already registered.
This technique is common in high-speed device drivers, such as network or disk, where the time lost in returning to the pre-interrupt task is greater than the time until the next required servicing. (Common I/O hardware in use these days relies heavily upon DMA and large data buffers to make up for a relatively poorly-performing interrupt system.