RFR: 8229867: Re-examine synchronization usages in http and https protocol handlers [v2]
Daniel Fuchs
dfuchs at openjdk.java.net
Fri Oct 9 11:49:30 UTC 2020
> 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.
Daniel Fuchs has updated the pull request incrementally with one additional commit since the last revision:
8229867: Re-examine synchronization usages in http and https protocol handlers
Incorporated review feedback
-------------
Changes:
- all: https://git.openjdk.java.net/jdk/pull/558/files
- new: https://git.openjdk.java.net/jdk/pull/558/files/c8dc2ac9..ddfa2e6c
Webrevs:
- full: https://webrevs.openjdk.java.net/?repo=jdk&pr=558&range=01
- incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=558&range=00-01
Stats: 35 lines in 8 files changed: 15 ins; 14 del; 6 mod
Patch: https://git.openjdk.java.net/jdk/pull/558.diff
Fetch: git fetch https://git.openjdk.java.net/jdk pull/558/head:pull/558
PR: https://git.openjdk.java.net/jdk/pull/558
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