code review 59220048: leveldb-go: implement file lock on FreeBSD.

leveldb-go: implement file lock on FreeBSD.

I do not believe FreeBSD requires a 32-bit and 64-bit version like Linux
for the following reasons (although I don't have a 32-bit FreeBSD box to
test on).

According to this, off_t is the same size on 32 and 64-bit, and not like linux's two APIs for everything to support LARGEFILE:

http://freecode.com/articles/largefile-support-problems

pid_t is an __int32_t, independent of arch AFAICT https://github.com/freebsd/freebsd/blob/master/sys/sys/_types.h

Type and Whence being shorts made me a bit nervous. This test on my 64-bit machines:

    $ cat short.c

    #include

    int main() {
        printf("sizeof short %lu\n", sizeof(short));
    }

    $ rm short; make CC=gcc short; ./short; rm short; make CC=clang short; ./short
    gcc -O2 -pipe -fno-omit-frame-pointer   short.c  -o short
    sizeof short 2
    clang -O2 -pipe -fno-omit-frame-pointer   short.c  -o short
    sizeof short 2

Makes me think we're safe, as I believe short would be 16-bit on 32-bit, and was unsure about its size on 64-bit.

    $ cat int.c
    #include <stdio.h>

    int main() {
        printf("sizeof int %lu\n", sizeof(int));
    }

    $ rm int; make CC=gcc int; ./int; rm int; make CC=clang int; ./int
    gcc -O2 -pipe -fno-omit-frame-pointer   int.c  -o int
    sizeof int 4
    clang -O2 -pipe -fno-omit-frame-pointer   int.c  -o int
    sizeof int 4

So int is 32-bit on FreeBSD even on 64-bit machines.

Running go test code.google.com/p/leveldb-go/... passes, as does filelock, i.e.:

    $ go run main.go /tmp/lock
    Locking /tmp/lock
    Unlocking /tmp/lock
    OK

[wathiede, 2014-02-08 22:02:22]

Hello golang-codereviews@googlegroups.com,

I'd like you to review this change to
https://code.google.com/p/leveldb-go

[nigeltao, 2014-02-18 05:49:20]

LGTM.

I presume that when you say that running filelock works, you run multiple
concurrent instances of filelock, not just one "go run main.go /tmp/lock".

[bradfitz, 2014-02-18 05:52:29]

Ideally the filelock test should invoke multiple child processes of itself.




On Mon, Feb 17, 2014 at 9:49 PM, <nigeltao@golang.org> wrote:

> LGTM.
>
> I presume that when you say that running filelock works, you run
> multiple concurrent instances of filelock, not just one "go run main.go
> /tmp/lock".
>
> https://codereview.appspot.com/59220048/
>
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[nigeltao, 2014-02-19 02:02:39]

*** Submitted as
https://code.google.com/p/leveldb-go/source/detail?r=b6ab03c49ef6 ***

    leveldb-go: implement file lock on FreeBSD.

I do not believe FreeBSD requires a 32-bit and 64-bit version like Linux
for the following reasons (although I don't have a 32-bit FreeBSD box to
test on).

According to this, off_t is the same size on 32 and 64-bit, and not like linux's
two APIs for everything to support LARGEFILE:

http://freecode.com/articles/largefile-support-problems

pid_t is an __int32_t, independent of arch AFAICT
https://github.com/freebsd/freebsd/blob/master/sys/sys/_types.h

Type and Whence being shorts made me a bit nervous. This test on my 64-bit
machines:

    $ cat short.c

    #include

    int main() {
        printf("sizeof short %lu\n", sizeof(short));
    }

    $ rm short; make CC=gcc short; ./short; rm short; make CC=clang short;
./short
    gcc -O2 -pipe -fno-omit-frame-pointer   short.c  -o short
    sizeof short 2
    clang -O2 -pipe -fno-omit-frame-pointer   short.c  -o short
    sizeof short 2

Makes me think we're safe, as I believe short would be 16-bit on 32-bit, and was
unsure about its size on 64-bit.

    $ cat int.c
    #include <stdio.h>

    int main() {
        printf("sizeof int %lu\n", sizeof(int));
    }

    $ rm int; make CC=gcc int; ./int; rm int; make CC=clang int; ./int
    gcc -O2 -pipe -fno-omit-frame-pointer   int.c  -o int
    sizeof int 4
    clang -O2 -pipe -fno-omit-frame-pointer   int.c  -o int
    sizeof int 4

So int is 32-bit on FreeBSD even on 64-bit machines.

Running go test code.google.com/p/leveldb-go/... passes, as does filelock, i.e.:

    $ go run main.go /tmp/lock
    Locking /tmp/lock
    Unlocking /tmp/lock
    OK

LGTM=nigeltao
R=golang-codereviews, nigeltao, bradfitz
CC=golang-codereviews
https://codereview.appspot.com/59220048

Committer: Nigel Tao <nigeltao@golang.org>

[wathiede, 2014-02-19 04:09:18]

On 2014/02/18 05:49:20, nigeltao wrote:
> LGTM.
> 
> I presume that when you say that running filelock works, you run multiple
> concurrent instances of filelock, not just one "go run main.go /tmp/lock".

Apologies, I failed to read the docstring of filelock/main.go, so I only ran one
copy.  As a consolation prize I've sent a CL implementing Brad's suggestion:

https://codereview.appspot.com/65870043

Which does pass with this CL when run on FreeBSD.