RFR: 8244936: Reduce JNI overhead of accessing FileDescriptor

[Claes Redestad]

On 2020-05-13 20:31, Alan Bateman wrote:
> On 13/05/2020 16:44, Claes Redestad wrote:
>> Hi,
>>
>> compilers can't see though and optimize away the repeated GetObjectField
>> calls in places such as in the io_util_md.h GET_FD macro:
>>
>> #define GET_FD(this, fid) \
>>     (*env)->GetObjectField(env, (this), (fid)) == NULL ? \
>>         -1 : (*env)->GetIntField(env, (*env)->GetObjectField(env, 
>> (this), (fid)), IO_fd_fdID)
>>
>> This can be avoided if we turn the macros into functions which call
>> GetObjectField only once:
>>
>> FD getFD(JNIEnv *env, jobject this, jfieldID fid) {
>>   jobject fd = (*env)->GetObjectField(env, this, fid);
>>   if (fd == NULL) {
>>     return -1;
>>   }
>>   return (*env)->GetIntField(env, fd, IO_fd_fdID);
>> }
>>
>> The similarly affected SET_FD is only used in one place, so I removed
>> that macro and applied the equivalent optimization at the call-site.
> The Windows implementation returns a HANDLE rather than an int fd so 
> there is a bit inconsistency when compared to the network code. This 
> pre-dates your change and technical debt that will need attention some 
> time. Your changes look good.

Right, FD is defined as jlong on Windows, int elsewhere. Since it's used
from shared code renaming it to HANDLE on Windows variant wouldn't work
- rather we'd need some type name that would capture the duality
(FD_OR_HANDLE?)

Thanks for the review!

/Claes