Use monotonic clock for relative timed waits#17
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The timedWaitVMWaitLock macro duplicates the deadline calculation already implemented by getTimeoutRelative(). Make the macro defer to the function instead, so relative timeout deadlines are computed in a single place. Signed-off-by: Guillermo Rodríguez <grodriguez@ingelabs.com>
The OpenJDK class library code probes CLOCK_MONOTONIC availability at runtime for use by JVM_NanoTime. Move the probe to common code (time.c), run it early in the VM initialisation sequence, and expose it as haveMonotonicClock(). Signed-off-by: Guillermo Rodríguez <grodriguez@ingelabs.com>
Introduce initReltimeCondVar() for initialising condition variables used with relative timeouts, and use it for all such condvars (the per-thread wait and park condvars, and VM-internal wait locks). A timed park (threadPark) can take either a relative timeout or an absolute wall-clock deadline, but currently both waits share the per-thread park condvar, and a condvar can only be bound to one clock. Split it in two: park_cv (relative and untimed parks) and park_cv_abs (absolute deadlines), choosing the right one when parking. Unparking signals both; signalling a condvar nobody waits on is harmless and cheap. All condvars are still bound to the default realtime clock, so no change in behaviour; this puts the infrastructure in place for switching relative timeouts to the monotonic clock. Signed-off-by: Guillermo Rodríguez <grodriguez@ingelabs.com>
All relative timeouts were computed against the wall clock, so stepping the system time backward stretched them and stepping it forward truncated them. Fix this by binding the condvars used for relative timed waits to CLOCK_MONOTONIC, if available, and make getTimeoutRelative() use the same clock when computing the deadline. If the monotonic clock cannot be used, behaviour is unchanged and a warning is printed at startup. Signed-off-by: Guillermo Rodríguez <grodriguez@ingelabs.com>
guillerodriguez
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phvega
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Jul 24, 2026
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