By opening a TraceContext it is now possible to set a logging tag that
will be automatically included into all subsequent log statements that
are done by the same thread. When the TraceContext is closed the tag is
unset.
A tag has a name and a value. Having multiple tags with the same name
but different values is possible.
Adding a tag with the same name and same value a second time is possible
but has no effect.
With this change open TraceContexts are not propagated to newly started
threads that do work in the background. Support for this will be
implemented by the follow-up change.
Example:
// Initially there are no tags
logger.atSevere().log("log without tag");
// a tag can be set by opening a TraceContext
try (TraceContext ctx = new TraceContext("tag1", "value1")) {
logger.atSevere().log("with tag1=value1");
// by opening another TraceContext a another tag can be added
try (TraceContext ctx2 = new TraceContext("tag2", "value2")) {
logger.atSevere().log("log with tag1=value1 and tag2=value2");
// it's possible to have same tag name with multiple values
try (TraceContext ctx3 = new TraceContext("tag2", "value2a")) {
logger.atSevere().log("log with tag1=value1, tag2=value2 and tag2=value2a");
// adding a tag with the same name and value of an existing tag has no effect
try (TraceContext ctx4 = new TraceContext("tag2", "value2a")) {
logger.atSevere().log("log with tag1=value1, tag2=value2 and tag2=value2a");
}
// closing ctx4 didn't remove tag2=value2a since it was set before opening ctx4
logger.atSevere().log("log with tag1=value1, tag2=value2 and tag2=value2a");
}
// closing ctx3 removed tag2=value2a
logger.atSevere().log("log with tag1=value1 and tag2=value2");
}
// closing ctx2 removed tag2=value2
logger.atSevere().log("with tag1=value1");
}
// closing ctx1 removed tag1=value1
logger.atSevere().log("log without tag");
To support logging tags we must register a LoggingContext in Flogger.
This is done by setting the 'flogger.logging_context' system property.
Change-Id: Ib01eb90b9ad832be0b2d794e14ce23bdef2f0fb6
Signed-off-by: Edwin Kempin <ekempin@google.com>
d92f6f754a