• Kagamin <spam here.lot> Oct 29 2009
• Kagamin <spam here.lot> Oct 29 2009
• Walter Bright <newshound1 digitalmars.com> Oct 29 2009

Kagamin <spam here.lot> writes:

Walter Bright Wrote:

 A function that accesses shared data has to put in fences. There's no 
 way to have the same code deal with shared and unshared code.


Shared code perfectly deals with unshared data (it's not guaranteed that shared
data is accessed by more than one thread). In other words unshared data is
implicitly castable to shared.

Kagamin <spam here.lot> writes:

Kagamin Wrote:

 Walter Bright Wrote:
 
 A function that accesses shared data has to put in fences. There's no 
 way to have the same code deal with shared and unshared code.


 Shared code perfectly deals with unshared data (it's not guaranteed that
shared data is accessed by more than one thread). In other words unshared data
is implicitly castable to shared.


Uh... this post was a little fast, ignore it, please.

Walter Bright <newshound1 digitalmars.com> writes:

Kagamin wrote:
 Walter Bright Wrote:
 A function that accesses shared data has to put in fences. There's
 no way to have the same code deal with shared and unshared code.


 Shared code perfectly deals with unshared data (it's not guaranteed
 that shared data is accessed by more than one thread). In other words
 unshared data is implicitly castable to shared.


Unfortunately, there is a subtle problem with that that makes such 
implicit casts unsafe. Shared data can be handed off to other threads. 
So if thread local data is implicitly cast to shared, then it can be 
handed off to other threads. Meaning it is no longer guaranteed to be 
thread local.