On 10/18/24 4:21 PM, Martin Frb via fpc-devel wrote:
On 18/10/2024 14:30, Michael Van Canneyt via fpc-devel wrote:
On Fri, 18 Oct 2024, Nikolay Nikolov via fpc-devel wrote:
On 10/18/24 12:10 AM, Martin Frb via fpc-devel wrote:
https://wiki.freepascal.org/Threadvar
If threads are used then a copy is made for each thread (including
the main thread). Note that the copy is made with the original
value of the variable, not with the value of the variable at the
time the thread is started.
But what is that original value? Since
threadvar
foo: integer = 1;
gives
Error: Cannot initialize variables declared as threadvar
I think the documentation is wrong. Threadvars are always
initialized as zero.
Then please explain what do copy_all_unit_threadvars and
copy_unit_threadvars do ?
This is called from InitThreadVars when a new thread is started.
Well, the docu may at least be confusing, or lacking some detail.
If indeed threadvars are always 0, then why copy a value, instead of
initializing it? (never mind the implementation details, but what it
will be to the end user).
Or maybe there is somewhere a way for (some?) threadvars to have a
different (initial) value? And that would presumingly then be, before
it is even copied to the main thread?
In C (with gcc) it's possible to give them initial value, other than 0:
__thread int i = 5;
But it doesn't seem to be supported by FPC for threadvars. And I don't
know about Delphi. FPC's thread initialization does indeed include code
for copying the initial values, when creating a thread. Maybe it's for
compatibility with thread-aware C libraries (including e.g. glibc),
linked with the program, or for a possible future support for
initialized threadvars in FPC?
Nikolay
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