site_archiver@lists.apple.com Delivered-To: Darwin-kernel@lists.apple.com User-agent: Alpine 1.00 (DEB 882 2007-12-20) Hi all, The code in question does this: void safe_sleep(int seconds) { struct timespec ts, tr; memset(&ts, 0, sizeof(ts)); ts.tv_sec = seconds; ts.tv_nsec = 0; while (nanosleep(&ts, &tr) == -1 && errno == EINTR) { BOX_TRACE("nanosleep interrupted with " << ts.tv_sec << "." << ts.tv_nsec << " secs remaining, sleeping again"); if (ts.tv_sec >= seconds) { BOX_WARNING("nanosleep returned with junk in " << "struct: " << ts.tv_sec << "." << ts.tv_nsec); return; } ts = tr; /* sleep again */ } } On OSX 10.6.2, I get the warning: nanosleep returned with junk in struct: 4294967295.999958431 int secs = (int32_t) tr.tv_sec; if (secs < 0) { BOX_WARNING("nanosleep interrupted late, " << secs << "." << tr.tv_nsec << " secs remaining"); return; } I see instead: nanosleep interrupted late, -1.999971228 secs remaining http://opensource.apple.com/source/Libc/Libc-583/gen/nanosleep.c /* This depends on the layout of a mach_timespec_t and timespec_t being equivalent */ ADD_MACH_TIMESPEC(¤t, requested_time); SUB_MACH_TIMESPEC(¤t, &remain); remaining_time->tv_sec = current.tv_sec; remaining_time->tv_nsec = current.tv_nsec; struct mach_timespec { unsigned int tv_sec; /* seconds */ clock_res_t tv_nsec; /* nanoseconds */ }; typedef struct mach_timespec mach_timespec_t; The SUB_MACH_TIMESPEC macro does: /* t1 -= t2 */ #define SUB_MACH_TIMESPEC(t1, t2) \ do { \ if (((t1)->tv_nsec -= (t2)->tv_nsec) < 0) { \ (t1)->tv_nsec += NSEC_PER_SEC; \ (t1)->tv_sec -= 1; \ } \ (t1)->tv_sec -= (t2)->tv_sec; \ } while (0) struct timespec is defined thus in sys/structs.h: #define _STRUCT_TIMESPEC struct timespec _STRUCT_TIMESPEC { __darwin_time_t tv_sec; long tv_nsec; }; and __darwin_time_t is defined as long in /usr/include/i386/_types.h: typedef long __darwin_time_t; /* time() */ So I wrote this test program: #include <mach/clock_types.h> #include <time.h> #include <stdio.h> int main(int argc, char** argv) { mach_timespec_t current, remain; current.tv_sec = 1267383159; current.tv_nsec = 300; remain.tv_sec = 1267383160; // 1.0000012 seconds later remain.tv_nsec = 1500; struct timespec requested_time, remaining_time; requested_time.tv_sec = 1; requested_time.tv_nsec = 0; ADD_MACH_TIMESPEC(¤t, &requested_time); SUB_MACH_TIMESPEC(¤t, &remain); remaining_time.tv_sec = current.tv_sec; remaining_time.tv_nsec = current.tv_nsec; int64_t remain_ns = (remaining_time.tv_sec * 1000000000) + remaining_time.tv_nsec; printf("remaining time (native tv_sec): %lld\n", remain_ns); remain_ns = ((long) remaining_time.tv_sec) * 1000000000; remain_ns += remaining_time.tv_nsec; printf("remaining time (long tv_sec): %lld\n", remain_ns); remain_ns = ((int32_t) remaining_time.tv_sec) * 1000000000; remain_ns += remaining_time.tv_nsec; printf("remaining time (int32_t tv_sec): %lld\n", remain_ns); return 0; } And it outputs: chris@jmac(~)$ ./test remaining time (native tv_sec): 4294967295999998800 remaining time (long tv_sec): 4294967295999998800 remaining time (int32_t tv_sec): -1200 Is this a bug, or did I misunderstand something? Please let me know. Cheers, Chris. -- _ ___ __ _ / __/ / ,__(_)_ | Chris Wilson <0000 at qwirx.com> - Cambs UK | / (_/ ,\/ _/ /_ \ | Security/C/C++/Java/Perl/SQL/HTML Developer | \ _/_/_/_//_/___/ | We are GNU-free your mind-and your software | _______________________________________________ Do not post admin requests to the list. They will be ignored. Darwin-kernel mailing list (Darwin-kernel@lists.apple.com) Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/darwin-kernel/site_archiver%40lists.a... I'm developing open source software that runs on MacOS among other platforms. I recently discovered a problem where code that works fine on other platforms is hanging indefinitely on OSX 10.6.2. I'm sure it worked in 10.3 on PPC hardware. And before I added a test for this condition, it would loop and sleep again for 4294967295 seconds, i.e. hang forever. I noticed that 4294967295 looks suspiciously like the int32_t representation of -1 treated as unsigned (cast to uint32_t). When I added the following code to check for this: and the loop does exit. Looking at the code for nanosleep in libc, which you can find here: and noting that the first version, for__DARWIN_UNIX03, appears to be used in this case, as gdb interrupts the hung process in __semwait_signal(), I can see that it does integer arithmetic on a mach_timespec_t structure, whose values are then assigned to the returned structure: First of all, the comment raised my suspicions, although the macros access the members directly so the actual memory layouts do not need to be identical. mach_timespec_t appears to be defined thus: (I cannot find this on the web, I copied it from /usr/include/mach/clock_types.h on this OSX 10.6.2 box). Since long is a 64-bit type on this platform, the value it contains is not appropriate. Only treating it as a 32-bit signed type gives the correct value. This email sent to site_archiver@lists.apple.com