fix undefined symbol: gettid #2389

[silencewood]

#2389
gettid
Glibc does not provide a wrapper for this system call; call it using syscall(2).

   #define _GNU_SOURCE
   #include <unistd.h>
   #include <sys/syscall.h>
   #include <sys/types.h>

   int
   main(int argc, char *argv[])
   {
       pid_t tid;

       tid = syscall(SYS_gettid);
   }

[dbwiddis]

Thanks for your contribution! Comments inline. Also please add a change log entry.

[dbwiddis]

I played around with some microbenchmarking, with the syscall method vs. resolving the dynamic link of /proc/thread-self:

syscall = LinuxLibc.INSTANCE.syscall(code).intValue();
// vs.
proctask = ParseUtil.parseIntOrDefault(Files.readSymbolicLink(link).getFileName().toString(), 0);

Not much difference between them, and pretty sure the proc approach is more portable.

  Method     TID      Nanos
 syscall   27693   10589.64
proctask   27693   12773.40

[dbwiddis]

Another test on an x86 system including the gettid native:

  Method     TID      Nanos
  gettid  955738     762.50
 syscall  955738    1836.52
proctask  955738    2543.79

[dbwiddis]

Thanks for your contribution! I made a few tweaks and merged it.

Let me know if there are any other changes needed, I'll probably get a release out tomorrow.

[dbwiddis]

• x86_64: 0xba = 186
• x86 or arm: 0xe0 = 224
• arm64: 0xb2 = 178

Digging into this again from primary headers and not a summary page, I think this is slightly off.

• arm64 is 224
• x86 is 224
• x86_64 is 186
• generic (fallback for non-intel/non-arm) is 178

I'll submit a quick fix for this.