select.h File Reference

Detailed Description

Provides the Select and SelectUntil functions for selecting a fiber to proceed if one of several cases is ready.

This file defines the thread::Select and thread::SelectUntil functions, which allow a fiber to wait for (block until) one of several cases happens to proceed, either until a specified deadline or indefinitely.

#include <absl/log/check.h>
#include "thread/cases.h"

Go to the source code of this file.

Functions
int	thread::SelectUntil (absl::Time deadline, const CaseArray &cases)
	Returns the index of the first case that is ready, or -1 if the deadline has expired without any case becoming ready.
int	thread::Select (const CaseArray &cases)
	Returns the index of the first case that is ready, blocking until one is.

Function Documentation

Select()

int thread::Select ( const CaseArray & cases )

inline

Returns the index of the first case that is ready, blocking until one is.

This is equivalent to calling SelectUntil with an infinite deadline.

Parameters

cases

The array of cases to select from. Usually passed as an initializer list.

Returns

The index of the first case that is ready, or -1 if no case is ready.

SelectUntil()

int thread::SelectUntil	(	absl::Time	deadline,
		const CaseArray &	cases )

Returns the index of the first case that is ready, or -1 if the deadline has expired without any case becoming ready.

Example:

// Try to write against the channel "c", waiting for up to 1ms when there is
// no space immediately available. Returns true if the write was
// successfully enqueued, false otherwise.
bool TryPut(thread::Channel<int>* c, int v) {
  return thread::SelectUntil(
      absl::Now() + absl::Milliseconds(1),
      {c->writer()->OnWrite(v)}) == 0;
  }

Note

If a Case transitions into a ready state after the deadline has expired, but before SelectUntil returns, the return value is not guaranteed to be -1 and may instead be the index of that case. However, if -1 is returned, it is guaranteed that no case has proceeded.

Parameters

deadline	The absolute time until which to wait for a case to become ready.
cases	The array of cases to select from. Usually passed as an initializer list.

Returns

The index of the first case that is ready, or -1 if the deadline has expired.