In which case task abc_2 will execute
semaphore sem = new(2);
task abc_1();
sem.get(2)
// DO
sem.put(1)
endtask
task abc_2();
sem.get(1)
// DO
sem.put(1)
endtask
CASE 1:
initial fork
abc_1();
abc_1();
abc_1();
abc_2();
join
CASE 2:
initial begin
abc_1();
abc_1();
abc_1();
abc_2();
end
SystemVerilog guarantees that abc_2 will not execute in CASE 2 because there is a defined execution ordering of statements within a begin/end block, and it will get stuck during the second call to abc_1.
However, there is no defined execution ordering of statements within a fork/join block. You might be able to deduce the particular ordering of a implementation, but you cannot rely on that ordering. An implementation that chooses to first execute the last statement as it appears in the source will call abc_2.
In reply to dariof:
I mean the code that executes as a result of compiling your source descriptions. The implementation can vary by tool version, platform and OS that where the code executes.