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ircd::ctx: Add ctx::critical_indicator.

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This commit is contained in:
Jason Volk 2018-05-07 12:38:24 -07:00
parent 5000397f12
commit e205755d5e
2 changed files with 23 additions and 0 deletions
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1
include/ircd/ctx/ctx.h
View file

@ -105,4 +105,5 @@ namespace ircd
using ctx::use_future;
using ctx::critical_assertion;
using ctx::critical_indicator;
}

22
include/ircd/ctx/this_ctx.h
View file

@ -15,6 +15,7 @@ namespace ircd::ctx {
/// Interface to the currently running context
inline namespace this_ctx
{
struct critical_indicator; // Indicates if yielding happened for a section
struct critical_assertion; // Assert no yielding for a section
struct exception_handler; // Must be present to yield in a handler
@ -91,6 +92,27 @@ class ircd::ctx::this_ctx::critical_assertion
#endif
};
/// An instance of critical_indicator reports if context switching happened.
///
/// A critical_indicator remains true after construction until a context switch
/// has occurred. It then becomes false. This is not an assertion and is
/// available in optimized builds for real use. For example, a context may
/// want to recompute some value after a context switch and opportunistically
/// skip this effort when this indicator shows no switch occurred.
///
class ircd::ctx::this_ctx::critical_indicator
{
uint64_t state;
public:
uint64_t count() const { return yields(cur()) - state; }
operator bool() const { return yields(cur()) == state; }
critical_indicator()
:state{yields(cur())}
{}
};
/// An instance of exception_handler must be present to allow a context
/// switch inside a catch block. This is due to ABI limitations that stack
/// exceptions with thread-local assumptions and don't expect catch blocks