Can You Select on Both Sending and Receiving Channels in Go, Without Blocking?

Selecting on Bidirectional Channels for Conditional Sending and Receiving

In Go, it's possible to set up buffered channels for both sending and receiving, allowing selective operations based on their availability. Consider the following scenario:

<code class="go">s := make(chan<p>We have a buffered send channel s and an unbuffered receive channel r. The question arises: can we select on both channels to determine if r has data or s is not full? This mimics the functionality of the following, but without consuming 100% CPU:</p>
<pre class="brush:php;toolbar:false"><code class="go">for {
    if len(s)  0 {
        // Receive something
    }
}</code>

Implementing Select with a Default Case

To achieve this, we can utilize the select statement with a default case. In the default case, if neither channel is ready, we temporarily "sleep" the goroutine to avoid unnecessary resource consumption.

<code class="go">s := make(chan<p><strong>Why Length and Capacity Checks Are Not Ideal</strong></p>
<p>It's crucial to avoid checking the length or capacity of a channel before attempting to send or receive. This is because the channel's state can change between the time of checking and the actual operation, potentially leading to unexpected blocking. For instance:</p>
<pre class="brush:php;toolbar:false"><code class="go">if len(r) > 0 {
    // r is ready to receive

    // Other code...

    r </code>

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