libc-bottom-half/clocks/clock.c

   1 #define _WASI_EMULATED_PROCESS_CLOCKS
   2 #include <time.h>
   3 #include <wasi/api.h>
   4 #include <common/time.h>
   5
   6 _Static_assert(
   7     CLOCKS_PER_SEC == NSEC_PER_SEC,
   8     "This implementation assumes that `clock` is in nanoseconds"
   9 );
  10
  11 // Snapshot of the monotonic clock at the start of the program.
  12 static __wasi_timestamp_t start;
  13
  14 // Use a priority of 10 to run fairly early in the implementation-reserved
  15 // constructor priority range.
  16 __attribute__((constructor(10)))
  17 static void init(void) {
  18     (void)__wasi_clock_time_get(__WASI_CLOCKID_MONOTONIC, 0, &start);
  19 }
  20
  21 clock_t __clock(void) {
  22     // Use `MONOTONIC` instead of `PROCESS_CPUTIME_ID` since WASI doesn't have
  23     // an inherent concept of a process. Note that this means we'll incorrectly
  24     // include time from other processes, so this function is only declared by
  25     // the headers if `_WASI_EMULATED_PROCESS_CLOCKS` is defined.
  26     __wasi_timestamp_t now = 0;
  27     (void)__wasi_clock_time_get(__WASI_CLOCKID_MONOTONIC, 0, &now);
  28     return now - start;
  29 }
  30
  31 __attribute__((__weak__, __alias__("__clock")))
  32 clock_t clock(void);