/** The next byte to read. This is always less than or equal to [upstreamPos]. */
    private var sourcePos = 0L

    /**
     * Selects where to find the bytes for a read and read them. This is one of three sources.
     *
     * ## Upstream
     *
     * In this case the current thread is assigned as the upstream reader. We read bytes from

 * host platform (like Android). In July 2018 Android had 134 trusted root certificates for its HTTP
 * clients to trust.
 *
 * For example, in order to establish a secure connection to `https://www.squareup.com/`,
 * these three certificates are used.
 *
 * ```
 * www.squareup.com certificate:
 *
 * Common Name: www.squareup.com
 * Subject Alternative Names: www.squareup.com, squareup.com, account.squareup.com...

 * may cause corruption or runtime errors if not. It may however be shared amongst multiple OkHttpClient
 * instances.
 *
 * ## Cache Optimization
 *
 * To measure cache effectiveness, this class tracks three statistics:
 *
 *  * **[Request Count:][requestCount]** the number of HTTP requests issued since this cache was
 *    created.
 *  * **[Network Count:][networkCount]** the number of those requests that required network use.

You can build your own connection spec with a custom set of TLS versions and cipher suites. For example, this configuration is limited to three highly-regarded cipher suites. Its drawback is that it requires Android 5.0+ and a similarly current webserver.

```java
ConnectionSpec spec = new ConnectionSpec.Builder(ConnectionSpec.MODERN_TLS)

    }

    redQueue.execute("task three", 100.µs) {
      log += "three:run@${taskFaker.nanoTime} parallel=${taskFaker.isParallel}"
    }

    taskFaker.advanceUntil(0.µs)
    assertThat(log).isEmpty()

    taskFaker.advanceUntil(100.µs)
    assertThat(log).containsExactly(
      "one:run@100000 parallel=false",
      "two:run@100000 parallel=false",
      "three:run@100000 parallel=false",
    )

with Java.

We spent a lot of time and energy on retaining strict compatibility with OkHttp 3.x. We’re even
keeping the package name the same: `okhttp3`!

There are three kinds of compatibility we’re tracking:

 * **Binary compatibility** is the ability to compile a program against OkHttp 3.x, and then to run
   it against OkHttp 4.x. We’re using the excellent [japicmp][japicmp] library via its