[Info-vax] OS implementation languages

[Arne Vajhøj]

On 9/5/2023 3:31 PM, candycane wrote:
>   SC> I also have absolutely no idea what happens with signals if you run
>   SC> dd under Cygwin on Windows.
> 
> I'd guess theres no equivelant.

Cygwin apparently does emulate signals.

https://cygwin.com/cygwin-ug-net/highlights.html

<quote>
Signals

When a Cygwin process starts, the library starts a secondary thread for 
use in signal handling. This thread waits for Windows events used to 
pass signals to the process. When a process notices it has a signal, it 
scans its signal bitmask and handles the signal in the appropriate fashion.

Several complications in the implementation arise from the fact that the 
signal handler operates in the same address space as the executing 
program. The immediate consequence is that Cygwin system functions are 
interruptible unless special care is taken to avoid this. We go to some 
lengths to prevent the sig_send function that sends signals from being 
interrupted. In the case of a process sending a signal to another 
process, we place a mutex around sig_send such that sig_send will not be 
interrupted until it has completely finished sending the signal.

In the case of a process sending itself a signal, we use a separate 
semaphore/event pair instead of the mutex. sig_send starts by resetting 
the event and incrementing the semaphore that flags the signal handler 
to process the signal. After the signal is processed, the signal handler 
signals the event that it is done. This process keeps intraprocess 
signals synchronous, as required by POSIX.

Most standard UNIX signals are provided. Job control works as expected 
in shells that support it.
</quote>

Arne