Lazily create logging files to avoid creating empty files

[niqiangpro-cell]

commit for issue #745

[rm5248]

I like the idea of having this be opt-in - any thoughts @swebb2066 ?

[swebb2066]

I like the idea of having this be opt-in - any thoughts

I support the intent of this PR. I don't think empty log files (or directory creation) are useful when they are not used.

[niqiangpro-cell]

I fixed the compilation error. It looks like the workflows are waiting for maintainer approval. Could you please trigger or approve the CI run?

[swebb2066]

This section should be replaced with:
char* path = this->path.getAPRPath();

[swebb2066]

path is assigned in the FileOutputStreamPrivate constructor.

[swebb2066]

As it stands, this will break MultiprocessRollingFileAppender because it calls FileOutputStream::getFilePtr after a FileOutputStream is created.

Please also replace MultiprocessRollingFileAppenderPriv::log_file with FileOutputStreamPtr fileOutputStream, and remove all resets of log_file (and associated comments). Then replace the single usage of log_file as follows.

diff --git a/src/main/cpp/multiprocessrollingfileappender.cpp b/src/main/cpp/multiprocessrollingfileappender.cpp
index 0b4bd42e..5ec5c68e 100644
--- a/src/main/cpp/multiprocessrollingfileappender.cpp
+++ b/src/main/cpp/multiprocessrollingfileappender.cpp
@@ -196,7 +196,7 @@ bool MultiprocessRollingFileAppender::isAlreadyRolled(const LogString& fileName,
        if (pSize)
                wantedInfo |= APR_FINFO_SIZE;
        apr_finfo_t finfo1;
-       apr_status_t st1 = apr_file_info_get(&finfo1, wantedInfo, _priv->log_file);
+       apr_status_t st1 = apr_file_info_get(&finfo1, wantedInfo, _priv->fileOutputStream->getFilePtr());

        if (st1 != APR_SUCCESS)
                LogLog::warn(LOG4CXX_STR("apr_file_info_get failed"));

[swebb2066]

Add a comment in the header file that this class assumes a single active thread.

The single active thread guarantee depends on the mutex lock in AppenderSkeleton::doAppend

[swebb2066]

Add a bool append parameter to the constructor

[swebb2066]

Remove the bool append parameters and use this->logAppend in the open methods.

[atari83]

So this laziness behavior for log file creation happens through an optional param/setting right ?
It'd be great to preserve existing mode (thick provisioning) and also have this for devs who want this feature.

Thanks.

[niqiangpro-cell]

So this laziness behavior for log file creation happens through an optional param/setting right ? It'd be great to preserve existing mode (thick provisioning) and also have this for devs who want this feature.

Thanks.

Good point. The current PR changes the behavior unconditionally, but I agree that we should preserve the existing behavior by default and make lazy file creation opt-in. I plan to add an optional setting on FileAppender (and derived file-based appenders), as file creation is really an appender concern. I'd be happy to hear any suggestions you may have.