On 5/22/15 2:36 AM, Suliman wrote:
On SO[1] I got next answer:
"What happens when you launch a D application ? The entry point is a C
main inside the runtime, which initialize it (the runtime), including
module constructor, run the unittest (if you've compiled with
-unittest), then call your main (which name is "_Dmain" - useful to know
if you want to set a breakpoint with GDB). When Vibe.d's main is called,
it parses command line argument, an optional config file, and finally,
starts the event loop. Any code that wish to run once the event loop has
started should use runTask and similar, or createTimer. They should not
call the code directly from the static constructor (it's actually one of
the most common mistake when starting with Vibe.d)."
Could you explain what mean "C main inside the runtime". I thought that
is only one main is possible. And why it's named "*ะก* main" D is not
C-translated language.
Same question is about _Dmain -- what is it?
If I will call this() before main? What it will be? Will it run before
main?
Druntime defines the main function that C runtime will call. C runtime
intializes its own things (e.g. stdin/stdout/stderr) and then calls C main.
Druntime's version of C main then intializes all things that D needs
(and there's quite a bit) not in any specific order:
- set up the main thread
- initialize the GC
- detect module constructor/destructor cycles
- run module constructors (both shared and thread-local)
- run unittests if enabled
- run your main function (defined in D as 'main')
After main exits, it unwinds all this stuff.
FYI, I didn't realize this (but just figured it out), C main *used* to
be in druntime, but it's now generated by the compiler. See here:
https://github.com/D-Programming-Language/dmd/blob/master/src/mars.c#L236
The function it calls (_d_run_main) is now the entry point into
druntime, and it is here:
https://github.com/D-Programming-Language/druntime/blob/master/src/rt/dmain2.d#L290
It can give you more clues as to how it works.
-Steve
