asharing: Don't start recording until all threads are running

This eliminates a bunch of confusing scopes that come from thread creation

asharing: Don't start recording until all threads are running
69cbd10a · Austin Clements · Silas Boyd-Wickizer · 87304b5d · 69cbd10a
--- a/bin/asharing.cc
+++ b/bin/asharing.cc
@@ -8,8 +8,10 @@

 #include <sys/mman.h>

+#include "atomic.hh"
+
 static int cpu;
-static pthread_barrier_t bar;
+std::atomic<int> barrier;
 enum { ncore = 8 };

 void
@@ -23,11 +25,26 @@ next()
  cpu++;
 }

+void
+ready(void)
+{
+  int slot = --barrier;
+  if (slot == 1) {
+    mtenable_type(mtrace_record_ascope, "xv6-asharing");
+    --barrier;
+  } else {
+    while (barrier)
+      asm volatile("pause");
+  }
+}
+
 void*
 vmsharing(void* arg)
 {
  u64 i = (u64) arg;

+  ready();
+
  volatile char *p = (char*)(0x40000UL + i * 4096);
  if (mmap((void *) p, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) < 0)
    die("mmap failed");
@@ -52,7 +69,7 @@ fssharing(void* arg)

  open(filename, O_CREATE|O_RDWR);

-  pthread_barrier_wait(&bar);
+  ready();

  for (u64 j = 0; j < ncore; j++) {
    snprintf(filename, sizeof(filename), "f%d", j);
@@ -73,8 +90,7 @@ main(int ac, char **av)
    fprintf(1, "usage: %s vm|fs\n", av[0]);

  if (op) {
-    mtenable_type(mtrace_record_ascope, "xv6-asharing");
-    pthread_barrier_init(&bar, 0, ncore);
+    barrier = ncore + 1;
    for (u64 i = 0; i < ncore; i++) {
      next();
      pthread_t tid;
@@ -83,6 +99,8 @@ main(int ac, char **av)

    for (u64 i = 0; i < ncore; i++)
      wait();
+    if (barrier)
+      die("forgot to call ready()");
    mtdisable("xv6-asharing");
  }
 }