diff -r a062c3691003 -r 917873d2983d src/os/solaris/vm/os_solaris.cpp --- a/src/os/solaris/vm/os_solaris.cpp Mon May 05 15:10:43 2014 +0200 +++ b/src/os/solaris/vm/os_solaris.cpp Fri Apr 25 07:40:33 2014 +0200 @@ -415,11 +415,7 @@ static hrtime_t first_hrtime = 0; static const hrtime_t hrtime_hz = 1000*1000*1000; -const int LOCK_BUSY = 1; -const int LOCK_FREE = 0; -const int LOCK_INVALID = -1; static volatile hrtime_t max_hrtime = 0; -static volatile int max_hrtime_lock = LOCK_FREE; // Update counter with LSB as lock-in-progress void os::Solaris::initialize_system_info() { @@ -1534,58 +1530,31 @@ } -// gethrtime can move backwards if read from one cpu and then a different cpu -// getTimeNanos is guaranteed to not move backward on Solaris -// local spinloop created as faster for a CAS on an int than -// a CAS on a 64bit jlong. Also Atomic::cmpxchg for jlong is not -// supported on sparc v8 or pre supports_cx8 intel boxes. -// oldgetTimeNanos for systems which do not support CAS on 64bit jlong -// i.e. sparc v8 and pre supports_cx8 (i486) intel boxes -inline hrtime_t oldgetTimeNanos() { - int gotlock = LOCK_INVALID; - hrtime_t newtime = gethrtime(); - - for (;;) { -// grab lock for max_hrtime - int curlock = max_hrtime_lock; - if (curlock & LOCK_BUSY) continue; - if (gotlock = Atomic::cmpxchg(LOCK_BUSY, &max_hrtime_lock, LOCK_FREE) != LOCK_FREE) continue; - if (newtime > max_hrtime) { - max_hrtime = newtime; - } else { - newtime = max_hrtime; - } - // release lock - max_hrtime_lock = LOCK_FREE; - return newtime; - } -} -// gethrtime can move backwards if read from one cpu and then a different cpu -// getTimeNanos is guaranteed to not move backward on Solaris +// gethrtime() should be monotonic according to the documentation, +// but some virtualized platforms are known to break this guarantee. +// getTimeNanos() must be guaranteed not to move backwards, so we +// are forced to add a check here. inline hrtime_t getTimeNanos() { - if (VM_Version::supports_cx8()) { - const hrtime_t now = gethrtime(); - // Use atomic long load since 32-bit x86 uses 2 registers to keep long. - const hrtime_t prev = Atomic::load((volatile jlong*)&max_hrtime); - if (now <= prev) return prev; // same or retrograde time; - const hrtime_t obsv = Atomic::cmpxchg(now, (volatile jlong*)&max_hrtime, prev); - assert(obsv >= prev, "invariant"); // Monotonicity - // If the CAS succeeded then we're done and return "now". - // If the CAS failed and the observed value "obs" is >= now then - // we should return "obs". If the CAS failed and now > obs > prv then - // some other thread raced this thread and installed a new value, in which case - // we could either (a) retry the entire operation, (b) retry trying to install now - // or (c) just return obs. We use (c). No loop is required although in some cases - // we might discard a higher "now" value in deference to a slightly lower but freshly - // installed obs value. That's entirely benign -- it admits no new orderings compared - // to (a) or (b) -- and greatly reduces coherence traffic. - // We might also condition (c) on the magnitude of the delta between obs and now. - // Avoiding excessive CAS operations to hot RW locations is critical. - // See http://blogs.sun.com/dave/entry/cas_and_cache_trivia_invalidate - return (prev == obsv) ? now : obsv ; - } else { - return oldgetTimeNanos(); - } + const hrtime_t now = gethrtime(); + const hrtime_t prev = max_hrtime; + if (now <= prev) { + return prev; // same or retrograde time; + } + const hrtime_t obsv = Atomic::cmpxchg(now, (volatile jlong*)&max_hrtime, prev); + assert(obsv >= prev, "invariant"); // Monotonicity + // If the CAS succeeded then we're done and return "now". + // If the CAS failed and the observed value "obsv" is >= now then + // we should return "obsv". If the CAS failed and now > obsv > prv then + // some other thread raced this thread and installed a new value, in which case + // we could either (a) retry the entire operation, (b) retry trying to install now + // or (c) just return obsv. We use (c). No loop is required although in some cases + // we might discard a higher "now" value in deference to a slightly lower but freshly + // installed obsv value. That's entirely benign -- it admits no new orderings compared + // to (a) or (b) -- and greatly reduces coherence traffic. + // We might also condition (c) on the magnitude of the delta between obsv and now. + // Avoiding excessive CAS operations to hot RW locations is critical. + // See https://blogs.oracle.com/dave/entry/cas_and_cache_trivia_invalidate + return (prev == obsv) ? now : obsv; } // Time since start-up in seconds to a fine granularity.