问题
OkHttp自定义重试拦截器常见实现方式：
private static class RetryInterceptor implements Interceptor {
@Override
public okhttp3.Response intercept(Chain chain) throws IOException {
int retryCount = 0;
Request request = chain.request();
okhttp3.Response response = chain.proceed(request);
while (!response.isSuccessful() && retryCount < RETRY_MAX_COUNT) {
retryCount++;
response = chain.proceed(request);
}
return response;
}
}
但是没有人告诉我，在3.14.x版本上会出现这个异常：
AndroidRuntime: java.lang.IllegalStateException: cannot make a new request because the previous response is still open: please call response.close()
第一反应去OkHttp的issue查查，果然有和我同病相怜的： https://github.com/square/okhttp/issues/4986
解决
while (!response.isSuccessful() && retryCount < RETRY_MAX_COUNT) {
retryCount++;
response.close(); // 很简单，加上这一句
response = chain.proceed(request);
}
调查
虽说很快就解决了，但是要是异常提示不告诉你要close呢，我们就要自己去探索了。所以还是忍不住扒下来源码看了看，搜索这个异常提示位于： okhttp/src/main/java/okhttp3/internal/connection/Transmitter.java 可以看到，是在newExchange方法中抛出的异常：
/** Returns a new exchange to carry a new request and response. */
Exchange newExchange(Interceptor.Chain chain, boolean doExtensiveHealthChecks) {
synchronized (connectionPool) {
if (noMoreExchanges) {
throw new IllegalStateException("released");
}
if (exchange != null) {
throw new IllegalStateException("cannot make a new request because the previous response "
+ "is still open: please call response.close()");
}
}
……
}
为了简单点，我们就直接搜索exchange在什么时候置的空，之所以response.close()能解决问题那就说明close方法最终会调用到exchange = null。查出来2个地方：
// 第一个调用处是来自RetryAndFollowUpInterceptor这一内部重试实现，此处可以忽略
public void exchangeDoneDueToException() {
synchronized (connectionPool) {
if (noMoreExchanges) throw new IllegalStateException();
exchange = null;
}
}
// 这个方法应该才是最终调用
@Nullable IOException exchangeMessageDone(
Exchange exchange, boolean requestDone, boolean responseDone, @Nullable IOException e) {
boolean exchangeDone = false;
synchronized (connectionPool) {
if (exchange != this.exchange) {
return e; // This exchange was detached violently!
}
boolean changed = false;
if (requestDone) {
if (!exchangeRequestDone) changed = true;
this.exchangeRequestDone = true;
}
if (responseDone) {
if (!exchangeResponseDone) changed = true;
this.exchangeResponseDone = true;
}
// 其实从这里的语义就能看出，只有responseDone了，exchange才会置空，正好对应response.close()
if (exchangeRequestDone && exchangeResponseDone && changed) {
exchangeDone = true;
this.exchange.connection().successCount++;
this.exchange = null;
}
}
if (exchangeDone) {
e = maybeReleaseConnection(e, false);
}
return e;
}
回溯一部分调用路径： ResponseBodySource#close -> complete --> Exchange#bodyComplete --> Transmitter#exchangeMessageDone 然后从Response的close方法开始看： 其实就是调用了ResponseBody的close：
@Override public void close() {
Util.closeQuietly(source());
}
// source是一个抽象方法，返回的BufferedSource是一个Closeable
public abstract BufferedSource source();
RealResponseBody进行了实现：
public final class RealResponseBody extends ResponseBody {
……
private final BufferedSource source;
public RealResponseBody(
@Nullable String contentTypeString, long contentLength, BufferedSource source) {
this.contentTypeString = contentTypeString;
this.contentLength = contentLength;
this.source = source;
}
……
@Override public BufferedSource source() {
return source;
}
}
正好对应Exchange的openResponseBody方法：
public ResponseBody openResponseBody(Response response) throws IOException {
try {
……
ResponseBodySource source = new ResponseBodySource(rawSource, contentLength);
// 将ResponseBodySource的实例作为RealResponseBody的source传入
return new RealResponseBody(contentType, contentLength, Okio.buffer(source));
} catch (IOException e) {
eventListener.responseFailed(call, e);
trackFailure(e);
throw e;
}
}
调用就这样合龙了。 所以我们调用Response#close方法最终就会走到Transmitter#exchangeMessageDone，对exchange置空，这样就不会抛出那个异常了。
