Use monotonic clock for sleep (WebAssembly#753)

Currently, `sleep` calls `clock_nanosleep` with `CLOCK_REALTIME`, which
unconditionally returns `ENOTSUP` on WASIp{2,3}. This PR changes this to
use `CLOCK_MONOTONIC`.

Author: TartanLlama

libc-bottom-half/cloudlibc/src/libc/time/clock_nanosleep.c

@@ -41,7 +41,7 @@ int clock_nanosleep(clockid_t clock_id, int flags, const struct timespec *rqtp,
   // Note: rmtp is ignored
 
   if (clock_id != CLOCK_MONOTONIC) {
-    // wasip2 only provides a pollable for monotonic clocks
+    // wasip{2,3} only provide a pollable for monotonic clocks
     return ENOTSUP;
   }
 

libc-bottom-half/cloudlibc/src/libc/time/nanosleep.c

@@ -8,7 +8,7 @@
 
 int nanosleep(const struct timespec *rqtp, struct timespec *rem) {
 #if defined(__wasip2__) || defined(__wasip3__)
-  // FIXME(WebAssembly/WASI#857): wasip2 only supports the monotonic clock for
+  // FIXME(WebAssembly/WASI#857): wasip2/p3 only supports the monotonic clock for
   // sleeping.
   clockid_t clock = CLOCK_MONOTONIC;
 #else

libc-bottom-half/cloudlibc/src/libc/unistd/sleep.c

@@ -4,10 +4,20 @@
 
 #include <time.h>
 #include <unistd.h>
+#include <wasi/version.h>
 
 unsigned int sleep(unsigned int seconds) {
   struct timespec ts = {.tv_sec = seconds, .tv_nsec = 0};
-  if (clock_nanosleep(CLOCK_REALTIME, 0, &ts, NULL) != 0)
+  // FIXME(WebAssembly/WASI#857): wasip2/p3 only supports the monotonic clock for
+  // sleeping.
+  #if defined(__wasip1__)
+  clockid_t clock_id = CLOCK_REALTIME;
+  #elif defined(__wasip2__) || defined(__wasip3__)
+  clockid_t clock_id = CLOCK_MONOTONIC;
+  #else
+  #error "Unsupported WASI version"
+  #endif
+  if (clock_nanosleep(clock_id, 0, &ts, NULL) != 0)
     return seconds;
   return 0;
 }

test/CMakeLists.txt

@@ -298,6 +298,7 @@ add_wasilibc_test(rewinddir.c FS FAILP3)
 add_wasilibc_test(seekdir.c FS FAILP3)
 add_wasilibc_test(usleep.c)
 add_wasilibc_test(nanosleep.c)
+add_wasilibc_test(sleep.c)
 add_wasilibc_test(write.c FS FAILP3)
 add_wasilibc_test(wasi-defines.c)
 

test/src/sleep.c

@@ -0,0 +1,38 @@
+#include "test.h"
+#include <errno.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <sys/time.h>
+#include <time.h>
+#include <wasi/version.h>
+
+#define TEST(c)                                                                \
+  do {                                                                         \
+    errno = 0;                                                                 \
+    if (!(c))                                                                  \
+      t_error("%s failed (errno = %d)\n", #c, errno);                          \
+  } while (0)
+
+#ifdef __wasip1__
+#define CLOCK CLOCK_REALTIME
+#else
+#define CLOCK CLOCK_MONOTONIC
+#endif
+
+int main(void) {
+  // Sleep for a total of 2 seconds
+  unsigned int seconds_to_sleep = 2;
+
+  struct timespec start_time, end_time;
+  clock_gettime(CLOCK, &start_time);
+  TEST(sleep(seconds_to_sleep) == 0);
+  clock_gettime(CLOCK, &end_time);
+  TEST(end_time.tv_sec - start_time.tv_sec <= 3);
+
+  long nanoseconds_elapsed = (end_time.tv_sec - start_time.tv_sec) * 1E9 -
+                             start_time.tv_nsec + end_time.tv_nsec;
+
+  TEST(nanoseconds_elapsed >= seconds_to_sleep * 1E9);
+
+  return t_status;
+}