Portability Note: In many older Unix systems,this condition was indicated by EWOULDBLOCK,which was a distinct error code different from EAGAIN. To make your program portable,you should check for both codes and treat them the same.
http://lists.parisc-linux.org/hypermail/parisc-linux/9895.html
On some SysV systems EAGAIN != EWOULDBLOCK. I think we inherited the
errno definitions from HPUX…
较老的AIX也是这样的系统:http://programming.itags.org/unix-linux-programming/81597/
HP-UX (and older versions of AIX)
对于AIX,我找到了代码列表:http://homepage3.nifty.com/owl_h0h0/unix/job/UNIX/tutorial/error.html
11 EAGAIN;
54 EWOULDBLOCK
OS / 390也是:http://web.archiveorange.com/archive/v/zvbaIz8u6TzsQHHjfzOi
OS/390 and other platforms where EWOULDBLOCK != EAGAIN
有更丰富的表:http://www.ioplex.com/~miallen/errcmp.html
SUSv3 AIX 4.3,5.1 HP-UX 11.22 Solaris 9,10 Linux 2.4.28,2.6.9 IRIX 6.5[4] OSF1 FreeBSD 5.2.1 OSX 10.3.8 MSVC6 EAGAIN 1 0 Resource unavailable,try again [3] 11 Resource temporarily unavailable 11 No more processes 11 Resource temporarily unavailable 11 Try again 11 Resource temporarily unavailable 11 ditto 35 Resource temporarily unavailable 35 Resource temporarily unavailable 11 Resource temporarily unavailable EWOULDBLOCK 0.9 0 Operation would block [3] 54 Operation would block [2] 246 Operation would block 11 11 Operation would block 11 Resource temporarily unavailable 35 Operation would block 35 Operation would block 35 Operation would block
所以,AIX 4.3,5.1; HP-UX 11.22和OSF1对EAGAIN和EWOULDBLOCK使用不同的代码