[#absl-Barrier-Block]
= xref:absl.adoc[absl]::xref:absl/Barrier.adoc[Barrier]::Block
:relfileprefix: ../../
:mrdocs:

Blocks the calling thread until the thread threshold is reached.

== Synopsis

Declared in `<absl/synchronization/barrier.h>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
bool
Block();
----

== Description

Blocks the current thread, and returns only when the `num_threads` threshold of threads utilizing this barrier has been reached. `Block()` returns `true` for precisely one caller, which may then destroy the barrier.

Memory ordering: For any threads X and Y, any action taken by X before X calls `Block()` will be visible to Y after Y returns from `Block()`.

== Return Value

`true` for exactly one caller (which may destroy the barrier), and `false` for all other callers.


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