[#XLOG_EVERY_N_THREAD]
= XLOG_EVERY_N_THREAD
:mrdocs:

Similar to XLOG(...) except only log a message every

== Synopsis

Declared in `<folly/logging/xlog.h>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
#define XLOG_EVERY_N_THREAD(level, n, ...)

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== Description

The internal counter is thread‐local, avoiding the contention which the XLOG_EVERY_N variations which use a global counter may suffer. If a given XLOG_EVERY_N or variation expansion is encountered concurrently by multiple threads in a hot code path and the global counter in the expansion is observed to be contended, then switching to XLOG_EVERY_N_THREAD can help.

Every thread that invokes this expansion has a counter for this expansion. The internal counters are all stored in a single thread‐local map to control TLS overhead, at the cost of a small runtime performance hit.

== Parameters

[cols="1,4"]
|===
| Name| Description
| *n*
| invocations per thread.
| *level*
| The `folly::LogLevel` value at which to log.
|===


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