Semaphore handles

The unique_semaphore semaphore handle wrapper is defined in wil/resource.h as part of the RAII resource wrappers library. It is a unique_any specialization that adds methods specific to the typical needs of dealing with a semaphore. There are three variants that can be chosen based upon the error handling style the calling code desires.

wil::unique_semaphore s1;           // failures throw
wil::unique_semaphore_nothrow s2;   // failures return HRESULTs
wil::unique_semaphore_failfast s3;  // failures terminate

// Create during construction (not allowed with unique_semaphore_nothrow)
wil::unique_semaphore s4(0, 4, L"MySemaphoreName");

// Standard operations
s1.ReleaseSemaphore();

// Standard operations when going out of scope:
auto releaseOnExit = s1.ReleaseSemaphore_scope_exit();

// Acquire semaphore and release when going out of scope:
auto releaseOnExit = s1.acquire();

// Create or Open a Semaphore
s1.create(0, 2);
s1.open(L"MySemaphoreName");
if (s1.try_create(0, 4, L"MySemaphoreName")) {}
if (s1.try_open(L"MySemaphoreName")) {}

When dealing with semaphore handles outside of unique_semaphore, WIL defines some simple methods to emulate the same RAII patterns:

// Release the semaphore when the returned value goes out of scope
auto releaseOnExit = wil::ReleaseSemaphore_scope_exit(handle);

See also

• Waiting on kernel objects