In my implementation, I actually have an additional queue of what I call open tasks. Whenever a task gets queued which cannot be run immediately (because it has dependencies or other child tasks), it gets added to this queue. Other tasks are run right away. Additionally, Work() is modified so that after a task has been worked upon, the thread tries to queue any of the open tasks, because they might now be able to run. Furthermore, while waiting on a task to be finished, the thread also tries to queue any of the open tasks.

This automatically handles the situation you described. There must always be a thread who pulls the last remaining, open task from the queue, even if it’s maybe the one and only task all others depend upon. As soon as that thread has finished working on that task, all the others will be able to run automatically.

Is this an unforseen problem? Or have I missed something that would prevent this from happening?

SomeLoggerClass myLogger(SomeOutputPolicy(arg1, arg2), ChannelFilter(channelToBeShown), OtherPolicy(arg1, arg2, arg3));

That’s how I do it in order to pass arguments to policies in all policy-based classes.

I recently started refactoring and overdoing a little logging and debugging framework I did once and just came accross your article. I always wanted to get started with policy based design and overdoing my old logging class based on your approach seems to be a good start for me.

Currently I´m kinda stuck with an architectural problem related to filtering.
If I understood correctly the Criteria struct takes care of storing all related data for filtering (in addition to the formatting data) like the verbose mode, log level, channel etc.
Now in case of the VerbosityFilter, i would implement the filter method like this for example:
struct FilterCriteria {
FilterCriteria() : channel(UNDEFINED), loglevel(UNDEFINED), verbosity(UNDEFINED) {}

struct LogLevelFilter {
bool filter(const FilterCriteria& criteria) {
if(criteria.loglevel == UNDEFINED || criteria.verbosity == UNDEFINED) {
return false;
} else if(criteria.loglevel >= criteria.verbosity) {
return true;
} else {
return false;
}
}
};

The verbosity level would be somewhere defined in the code and every time I log something I pass the defined verbosity level to the log() method from the logger. So if if have some static variable or define called VERBOSITY, I would always pass VERBOSITY to log und depending on VERBOSITY and the log level for each log, the log message is displayed or not.

Now coming to the Channelfilter I´m not sure how i should define the channel i want to filter within my Filter.
I dont want to add a channel() method within my logger since only Loggers with the Channerfilter policy are interested in the channel.
I also dont want to do something like this

struct LogSettings {
static uint32_t verbosity;
static uint32_t channel;
};
struct ChannelFilter {
bool filter(const FilterCriteria& criteria) {
if(criteria.channel == UNDEFINED) {
return false;
} else if(criteria.channel == LogSettings::channel) {
return true;
} else {
return false;
}
}
};

because all loggers would be bound to the LogSettings struct and I cannot tell Logger a to only filter by Channel “A” and Logger b to only filter by Channel “B”. This problem does not came into play with verbosity since the verbosity level can be shared by all loggers.

I hope i could state a clear question.

Regards Christian