On 01/13/10 17:15:10, Ian Lance Taylor wrote: [...] > Otherwise TLS variables are generated as definitions rather than as > common variables. > > Why do you want them to be common?
For GCC/UPC compiled programs there are two compilation modes: 1) Each UPC thread is implemented as a full process, and these processes might be distributed across a network. 2) Each UPC thread is implemented as an OS thread (ie, pthread), and they are created by a single process and execute within its address spec. In the "process model", "int x;" has the usual semantics. It is defined as a common symbol. In the "pthread model", each file scoped variable is "localized" and becomes thread local; this is implemented by defining the variable using TLS relocation. Intermixing previously compiled C code that refers to file scoped variables with GCC/UPC compiled "pthread mode" files will likely not work well. But if the C code is compiled with the GCC/UPC compiler in "pthread mode" all file scoped symbols will be localized and everything should work as expected. The "process model" is the more natural and preferred way to compile UPC programs. The pthread model can offer some efficiencies and can make it easier to debug the program. Given the above, the goal of compiling in pthreads mode is to be able to compile regular "C" code as is, with the same behavior as when it was compiled in the normal process model. Thus, we want to translate all file scoped variables into localized TLS variables with the fewest surprises and differences. > Personally I tend to think that that is a good > thing. Treating uninitialized variables as common variables is a > non-standard extension even for C90. We can't get rid of them for > existing code, but __thread code is by definition new. I agree with your statement above, but for our purposes things will work better if we do create commonized TLS symbols. Maybe we can use GOMP's method for creating commonized TLS variables. Thanks for pointing it out. Do you/others on this list have a reference that supports the statement: "Treating uninitialized variables as common variables is a non-standard extension even for C90."? (I did see a thread on this list, late April 1999, that discussed some of the issues, but nothing definitive.) thanks.
