sysinfo.cc: Always abort on GetNumCPUs failure (#1756)

Defines a wrapper function, CheckNumCPUs, which enforces that GetNumCPUs
never returns fewer than one CPU.  There is no reasonable way to
continue if we are unable to identify the number of CPUs.

Signed-off-by: Sam James <sam@gentoo.org>

Author: thesamesam

src/sysinfo.cc

@@ -474,12 +474,11 @@ std::string GetSystemName() {
 #endif  // Catch-all POSIX block.
 }
 
-int GetNumCPUs() {
+int GetNumCPUsImpl() {
 #ifdef BENCHMARK_HAS_SYSCTL
   int num_cpu = -1;
   if (GetSysctl("hw.ncpu", &num_cpu)) return num_cpu;
-  fprintf(stderr, "Err: %s\n", strerror(errno));
-  std::exit(EXIT_FAILURE);
+  PrintErrorAndDie("Err: ", strerror(errno));
 #elif defined(BENCHMARK_OS_WINDOWS)
   SYSTEM_INFO sysinfo;
   // Use memset as opposed to = {} to avoid GCC missing initializer false
@@ -493,8 +492,8 @@ int GetNumCPUs() {
   // Returns -1 in case of a failure.
   long num_cpu = sysconf(_SC_NPROCESSORS_ONLN);
   if (num_cpu < 0) {
-    fprintf(stderr, "sysconf(_SC_NPROCESSORS_ONLN) failed with error: %s\n",
-            strerror(errno));
+    PrintErrorAndDie("sysconf(_SC_NPROCESSORS_ONLN) failed with error: ",
+                     strerror(errno));
   }
   return (int)num_cpu;
 #elif defined(BENCHMARK_OS_QNX)
@@ -510,8 +509,7 @@ int GetNumCPUs() {
   int max_id = -1;
   std::ifstream f("/proc/cpuinfo");
   if (!f.is_open()) {
-    std::cerr << "failed to open /proc/cpuinfo\n";
-    return -1;
+    PrintErrorAndDie("Failed to open /proc/cpuinfo");
   }
 #if defined(__alpha__)
   const std::string Key = "cpus detected";
@@ -540,12 +538,10 @@ int GetNumCPUs() {
     }
   }
   if (f.bad()) {
-    std::cerr << "Failure reading /proc/cpuinfo\n";
-    return -1;
+    PrintErrorAndDie("Failure reading /proc/cpuinfo");
   }
   if (!f.eof()) {
-    std::cerr << "Failed to read to end of /proc/cpuinfo\n";
-    return -1;
+    PrintErrorAndDie("Failed to read to end of /proc/cpuinfo");
   }
   f.close();
 
@@ -559,6 +555,16 @@ int GetNumCPUs() {
   BENCHMARK_UNREACHABLE();
 }
 
+int GetNumCPUs() {
+  const int num_cpus = GetNumCPUsImpl();
+  if (num_cpus < 1) {
+    PrintErrorAndDie(
+        "Unable to extract number of CPUs.  If your platform uses "
+        "/proc/cpuinfo, custom support may need to be added.");
+  }
+  return num_cpus;
+}
+
 class ThreadAffinityGuard final {
  public:
   ThreadAffinityGuard() : reset_affinity(SetAffinity()) {