Use NumCPUsMaybe to gracefully handle missing /sys.

We use /sys to determine the number of CPUs we might see from restartable
sequences.  When this is not available, gracefully degrade rather than
check-failing.

Fixes #245.

PiperOrigin-RevId: 667702663
Change-Id: Id78f557913f5936f7c4515dcbc2d445e162f68e3

tcmalloc/internal/cache_topology.cc

@@ -55,7 +55,13 @@ int BuildCpuToL3CacheMap_FindFirstNumberInBuf(absl::string_view current) {
 }
 
 void CacheTopology::Init() {
-  cpu_count_ = NumCPUs();
+  const auto maybe_numcpus = NumCPUsMaybe();
+  if (!maybe_numcpus.has_value()) {
+    l3_count_ = 1;
+    return;
+  }
+
+  cpu_count_ = *maybe_numcpus;
   for (int cpu = 0; cpu < cpu_count_; ++cpu) {
     const int fd = OpenSysfsCacheList(cpu);
     if (fd == -1) {

tcmalloc/internal/cache_topology.h

@@ -43,7 +43,9 @@ class CacheTopology {
   unsigned GetL3FromCpuId(int cpu) const {
     TC_ASSERT_GE(cpu, 0);
     TC_ASSERT_LT(cpu, cpu_count_);
-    return l3_cache_index_[cpu];
+    unsigned l3 = l3_cache_index_[cpu];
+    TC_ASSERT_LT(l3, l3_count_);
+    return l3;
   }
 
  private:

tcmalloc/internal/parameter_accessors.h

@@ -75,6 +75,8 @@ ABSL_ATTRIBUTE_WEAK void TCMalloc_Internal_SetMaxTotalThreadCacheBytes(
 ABSL_ATTRIBUTE_WEAK void TCMalloc_Internal_SetPeakSamplingHeapGrowthFraction(
     double v);
 ABSL_ATTRIBUTE_WEAK void TCMalloc_Internal_SetPerCpuCachesEnabled(bool v);
+ABSL_ATTRIBUTE_WEAK void
+TCMalloc_Internal_SetPerCpuCachesEnabledNoBuildRequirement(bool v);
 ABSL_ATTRIBUTE_WEAK void TCMalloc_Internal_SetProfileSamplingInterval(
     int64_t v);
 ABSL_ATTRIBUTE_WEAK void TCMalloc_Internal_SetBackgroundProcessActionsEnabled(

tcmalloc/internal/percpu.cc

@@ -116,7 +116,12 @@ int VirtualCpu::Synchronize() {
 }
 
 static void InitPerCpu() {
-  TC_CHECK(NumCPUs() <= std::numeric_limits<uint16_t>::max());
+  const auto maybe_numcpus = NumCPUsMaybe();
+  if (!maybe_numcpus.has_value()) {
+    init_status = kSlowMode;
+    return;
+  }
+  TC_CHECK(*maybe_numcpus <= std::numeric_limits<uint16_t>::max());
 
   // Based on the results of successfully initializing the first thread, mark
   // init_status to initialize all subsequent threads.

tcmalloc/parameters.cc

@@ -570,6 +570,10 @@ void TCMalloc_Internal_SetPerCpuCachesEnabled(bool v) {
   }
 #endif  // !TCMALLOC_DEPRECATED_PERTHREAD
 
+  TCMalloc_Internal_SetPerCpuCachesEnabledNoBuildRequirement(v);
+}
+
+void TCMalloc_Internal_SetPerCpuCachesEnabledNoBuildRequirement(bool v) {
   Parameters::per_cpu_caches_enabled_.store(v, std::memory_order_relaxed);
 }
 

tcmalloc/parameters.h

@@ -213,7 +213,8 @@ class Parameters {
   friend void ::TCMalloc_Internal_SetMaxPerCpuCacheSize(int32_t v);
   friend void ::TCMalloc_Internal_SetMaxTotalThreadCacheBytes(int64_t v);
   friend void ::TCMalloc_Internal_SetPeakSamplingHeapGrowthFraction(double v);
-  friend void ::TCMalloc_Internal_SetPerCpuCachesEnabled(bool v);
+  friend void ::TCMalloc_Internal_SetPerCpuCachesEnabledNoBuildRequirement(
+      bool v);
   friend void ::TCMalloc_Internal_SetProfileSamplingInterval(int64_t v);
 
   friend void ::TCMalloc_Internal_SetHugePageFillerSkipSubreleaseInterval(

tcmalloc/static_vars.cc

@@ -39,6 +39,7 @@
 #include "tcmalloc/internal/logging.h"
 #include "tcmalloc/internal/mincore.h"
 #include "tcmalloc/internal/numa.h"
+#include "tcmalloc/internal/parameter_accessors.h"
 #include "tcmalloc/internal/percpu.h"
 #include "tcmalloc/internal/sysinfo.h"
 #include "tcmalloc/malloc_extension.h"
@@ -162,7 +163,9 @@ ABSL_ATTRIBUTE_COLD ABSL_ATTRIBUTE_NOINLINE void Static::SlowInitIfNecessary() {
     TC_CHECK(sizemap_.Init(SizeMap::CurrentClasses().classes));
     // Verify we can determine the number of CPUs now, since we will need it
     // later for per-CPU caches and initializing the cache topology.
-    (void)NumCPUs();
+    if (ABSL_PREDICT_FALSE(!NumCPUsMaybe().has_value())) {
+      TCMalloc_Internal_SetPerCpuCachesEnabledNoBuildRequirement(false);
+    }
     (void)subtle::percpu::IsFast();
     numa_topology_.Init();
     CacheTopology::Instance().Init();