[#BSLMT_ONCE_DO]
= BSLMT_ONCE_DO
:mrdocs:

This macro provides a simple control construct to bracket a piece of code that should only be executed once during the course of a multithreaded program. Usage: ` BSLMT_ONCE_DO { /* one‐time code goes here */ } ` Leaving a `BSLMT_ONCE_DO` construct via `break`, `continue`, or `return` will put the construct in a "done" state (unless `BSLMT_ONCE_CANCEL` has been called) and will unblock all threads waiting to enter the one‐time region. Note that a `break` or `continue` within the one‐time code will terminate only the `BSLMT_ONCE_DO` construct, not any surrounding loop or switch statement. Due to a bug in the Microsoft Visual C++ 2003 compiler, the behavior is undefined if an exception is thrown from within this construct and is not caught within the same construct. Only one call to `BSLMT_ONCE_DO` may appear on a single source‐code line in any code block.

== Synopsis

Declared in `<bslmt_once.h>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
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#define BSLMT_ONCE_DO

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