RFR: 8229867: Re-examine synchronization usages in http and https protocol handlers

[Daniel Fuchs]

On Fri, 9 Oct 2020 08:36:03 GMT, Chris Hegarty <chegar at openjdk.org> wrote:

>> Hi,
>> 
>> This is a fix that upgrades the old HTTP and HTTPS legacy stack to use virtual-thread friendly locking instead of
>> synchronized monitors.
>> Most of the changes are mechanical - but there are still a numbers of subtle non-mechanical differences that are
>> outlined below:
>> 1. src/java.base/share/classes/sun/net/www/MessageHeader.java:
>>    `MessageHeader::print(PrintStream)` => synchronization modified to not synchronize on this while printing
>>    ( a snapshot of the data is taken before printing instead)
>> 
>> 2. src/java.base/share/classes/sun/net/www/MeteredStream.java:
>>     `MeteredStream::close` was missing synchronization: it is now protected by the lock
>> 
>> 3. src/java.base/share/classes/sun/net/www/http/ChunkedOutputStream.java:
>>     `ChunkedOutputStream` no longer extends `PrintStream` but extends `OutputStream` directly.
>>     Extending `PrintStream` is problematic for virtual thread. After careful analysis, it appeared that
>>     `ChunkedOutputStream` didn't really need to extend `PrintStream`. `ChunkedOutputStream`
>>     is already wrapping a `PrintStream`.  `ChunkedOutputStream` is never returned directly to user
>>     code but is wrapped in another stream. `ChunkedOutputStream` completely reimplement and
>>     reverse the flush logic implemented by its old super class`PrintStream` which leads me to believe
>>     there was no real reason for it to extend `PrintStream` - except for being able to call its `checkError`
>>     method - which can be done by using `instanceof ChunkedOutputStream` in the caller instead of
>>     casting to PrintStream.
>> 
>> 4. src/java.base/share/classes/sun/net/www/http/HttpClient.java:
>>     Synchronization removed from `HttpClient::privilegedOpenServer` and replaced by an `assert`.
>>     There is no need for a synchronized here as the method is only called from a method that already
>>     holds the lock.
>> 
>> 5. src/java.base/share/classes/sun/net/www/http/KeepAliveCache.java:
>>     Synchronization removed from `KeepAliveCache::removeVector` and replaced by an `assert`.
>>     This method is only called from methods already protected by the lock.
>>     Also the method has been made private.
>> 
>> 6. src/java.base/share/classes/sun/net/www/http/KeepAliveStream.java
>>     `queuedForCleanup` is made volatile as it is read and written directly from outside the class
>>     and without protection by the `KeepAliveCleanerEntry`.
>>     Lock protection is also added to `close()`, which was missing it.
>>     Some methods that have no lock protection and did not need it because only called from
>>     within code blocks protected by the lock have aquired an `assert isLockHeldByCurrentThread();`
>> 
>> 7. Concrete subclasses of `AuthenticationInfo` that provide an implementation for
>>     `AuthenticationInfo::setHeaders(HttpURLConnection conn, HeaderParser p, String raw)` have
>>     acquired an `assert conn.isLockheldByCurrentThread();` as the method should only be called
>>     from within a lock-protected block in `s.n.w.p.h.HttpURLConnection`
>> 
>> 8. src/java.base/share/classes/sun/net/www/protocol/http/HttpURLConnection.java
>>     Several methods in this class have a acquired an `assert isLockheldByCurrentThread();`
>>     to help track the fact that AuthenticationInfo::setHeaders is only called while
>>     holding the lock.
>>     Synchronization was also removed from some method that didn't need it because only
>>     called from within code blocks protected by the lock:
>>     `getOutputStream0()`: synchronization removed and replaced by an `assert isLockheldByCurrentThread();`
>>     `setCookieHeader()`:  synchronization removed and replaced by an `assert isLockheldByCurrentThread();`
>>     `getInputStream0()`:  synchronization removed and replaced by an `assert isLockheldByCurrentThread();`
>>     `StreamingOutputStream`: small change to accomodate point 3. above (changes in ChunkedOutputStream).
>> 
>> 9. src/java.base/share/classes/sun/net/www/protocol/http/NegotiateAuthentication.java.:
>>     synchronization removed from `setHeaders` and replace by an assert. See point 7. above.
>> 
>> 10. src/java.base/unix/classes/sun/net/www/protocol/http/ntlm/NTLMAuthentication.java:
>>     synchronization removed from `setHeaders` and replace by an assert. See point 7. above.
>> 
>> 11. src/java.base/windows/classes/sun/net/www/protocol/http/ntlm/NTLMAuthentication.java:
>>     synchronization removed from `setHeaders` and replace by an assert. See point 7. above.
>
> src/java.base/share/classes/sun/net/www/MeteredStream.java line 123:
> 
>> 121:         lock();
>> 122:         try {
>> 123:             if (closed) return -1;
> 
> This double check of `closed` is kind of irritating. Is it really need, or maybe we just drop it and lock
> unconditionally?

We could.

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PR: https://git.openjdk.java.net/jdk/pull/558