Unhardcode tick-to-ms conversion

Division by 100000.0 worked because `sysconf(_SC_CLK_TCK)` happened to be 100.

By unhardcoding:

1) It becomes more clear what this 100000.0 figure comes from.
2) It protects against bugs in the case `sysconf(_SC_CLK_TCK)` ever changes.

darwin/DarwinProcess.c

@@ -292,23 +292,21 @@ void DarwinProcess_setFromKInfoProc(Process* proc, const struct kinfo_proc* ps,
    proc->updated = true;
 }
 
-void DarwinProcess_setFromLibprocPidinfo(DarwinProcess* proc, DarwinProcessList* dpl) {
+void DarwinProcess_setFromLibprocPidinfo(DarwinProcess* proc, DarwinProcessList* dpl, double time_interval) {
    struct proc_taskinfo pti;
 
    if (sizeof(pti) == proc_pidinfo(proc->super.pid, PROC_PIDTASKINFO, 0, &pti, sizeof(pti))) {
-      if (0 != proc->utime || 0 != proc->stime) {
-         uint64_t diff = (pti.pti_total_system - proc->stime)
-                       + (pti.pti_total_user - proc->utime);
+      uint64_t total_existing_time = proc->stime + proc->utime;
+      uint64_t total_current_time = pti.pti_total_system + pti.pti_total_user;
 
-         proc->super.percent_cpu = (double)diff * (double)dpl->super.cpuCount * Platform_timebaseToNS
-                                 / ((double)dpl->global_diff * 100000.0);
-
-//       fprintf(stderr, "%f %llu %llu %llu %llu %llu\n", proc->super.percent_cpu,
-//               proc->stime, proc->utime, pti.pti_total_system, pti.pti_total_user, dpl->global_diff);
-//       exit(7);
+      if (total_existing_time && 1e-6 < time_interval) {
+         uint64_t total_time_diff = total_current_time - total_existing_time;
+         proc->super.percent_cpu = ((double)total_time_diff / time_interval) * 100.0;
+      } else {
+         proc->super.percent_cpu = 0.0;
       }
 
-      proc->super.time = (pti.pti_total_system + pti.pti_total_user) / 10000000;
+      proc->super.time = total_current_time / 10000000;
       proc->super.nlwp = pti.pti_threadnum;
       proc->super.m_virt = pti.pti_virtual_size / ONE_K;
       proc->super.m_resident = pti.pti_resident_size / ONE_K;

darwin/DarwinProcess.h

@@ -34,7 +34,7 @@ bool Process_isThread(const Process* this);
 
 void DarwinProcess_setFromKInfoProc(Process* proc, const struct kinfo_proc* ps, bool exists);
 
-void DarwinProcess_setFromLibprocPidinfo(DarwinProcess* proc, DarwinProcessList* dpl);
+void DarwinProcess_setFromLibprocPidinfo(DarwinProcess* proc, DarwinProcessList* dpl, double time_interval);
 
 /*
  * Scan threads for process state information.

darwin/DarwinProcessList.c

@@ -21,6 +21,7 @@ in the source distribution for its full text.
 
 #include "CRT.h"
 #include "DarwinProcess.h"
+#include "Platform.h"
 #include "ProcessList.h"
 #include "zfs/openzfs_sysctl.h"
 #include "zfs/ZfsArcStats.h"
@@ -158,6 +159,11 @@ void ProcessList_delete(ProcessList* this) {
    free(this);
 }
 
+static double ticksToNanoseconds(const double ticks) {
+   const double nanos_per_sec = 1e9;
+   return ticks / (double) Platform_clockTicksPerSec * Platform_timebaseToNS * nanos_per_sec;
+}
+
 void ProcessList_goThroughEntries(ProcessList* super, bool pauseProcessUpdate) {
    DarwinProcessList* dpl = (DarwinProcessList*)super;
    bool preExisting = true;
@@ -185,6 +191,8 @@ void ProcessList_goThroughEntries(ProcessList* super, bool pauseProcessUpdate) {
       }
    }
 
+   const double time_interval = ticksToNanoseconds(dpl->global_diff) / (double) dpl->super.cpuCount;
+
    /* Clear the thread counts */
    super->kernelThreads = 0;
    super->userlandThreads = 0;
@@ -204,7 +212,7 @@ void ProcessList_goThroughEntries(ProcessList* super, bool pauseProcessUpdate) {
       proc = (DarwinProcess*)ProcessList_getProcess(super, ps[i].kp_proc.p_pid, &preExisting, DarwinProcess_new);
 
       DarwinProcess_setFromKInfoProc(&proc->super, &ps[i], preExisting);
-      DarwinProcess_setFromLibprocPidinfo(proc, dpl);
+      DarwinProcess_setFromLibprocPidinfo(proc, dpl, time_interval);
 
       // Disabled for High Sierra due to bug in macOS High Sierra
       bool isScanThreadSupported  = ! ( CompareKernelVersion(17, 0, 0) >= 0 && CompareKernelVersion(17, 5, 0) < 0);

darwin/Platform.c

@@ -10,16 +10,18 @@ in the source distribution for its full text.
 
 #include "Platform.h"
 
+#include <errno.h>
 #include <math.h>
 #include <stdlib.h>
-
-#include <CoreFoundation/CoreFoundation.h>
+#include <unistd.h>
 #include <CoreFoundation/CFString.h>
+#include <CoreFoundation/CoreFoundation.h>
 #include <IOKit/ps/IOPowerSources.h>
 #include <IOKit/ps/IOPSKeys.h>
 
 #include "ClockMeter.h"
 #include "CPUMeter.h"
+#include "CRT.h"
 #include "DarwinProcessList.h"
 #include "DateMeter.h"
 #include "DateTimeMeter.h"
@@ -112,6 +114,8 @@ const MeterClass* const Platform_meterTypes[] = {
 
 double Platform_timebaseToNS = 1.0;
 
+long Platform_clockTicksPerSec = -1;
+
 void Platform_init(void) {
    // Check if we can determine the timebase used on this system.
    // If the API is unavailable assume we get our timebase in nanoseconds.
@@ -122,6 +126,14 @@ void Platform_init(void) {
 #else
    Platform_timebaseToNS = 1.0;
 #endif
+
+   // Determine the number of clock ticks per second
+   errno = 0;
+   Platform_clockTicksPerSec = sysconf(_SC_CLK_TCK);
+
+   if (errno || Platform_clockTicksPerSec < 1) {
+      CRT_fatalError("Unable to retrieve clock tick rate");
+   }
 }
 
 void Platform_done(void) {

darwin/Platform.h

@@ -24,6 +24,8 @@ extern const ProcessField Platform_defaultFields[];
 
 extern double Platform_timebaseToNS;
 
+extern long Platform_clockTicksPerSec;
+
 extern const SignalItem Platform_signals[];
 
 extern const unsigned int Platform_numberOfSignals;