Export of internal Abseil changes

--
f3ac7ee28fc7de737bc9e2e1d10ff7739781d645 by Gennadiy Rozental <rogeeff@google.com>:

Internal change

PiperOrigin-RevId: 435739199
Change-Id: I8f854b742418a237f9060e4b9f23d0f20baf0bdf

--
fe1329708cb40da8e72e53e4eaad79112bdb79ea by Abseil Team <absl-team@google.com>:

Port SwissTable internals comments from github.com/google/cwisstable to Abseil.

PiperOrigin-RevId: 435719801
Change-Id: I2270cc93aaa5d3d57954a8cea7e570b72b6c3956

--
a6e6fcd4b944ce370ac3307e848645c27bf21e47 by Derek Mauro <dmauro@google.com>:

Internal change

PiperOrigin-RevId: 435716325
Change-Id: I77999f69e176ee6c0d18e7c3329a7c336164f0fc
GitOrigin-RevId: f3ac7ee28fc7de737bc9e2e1d10ff7739781d645

absl/container/internal/raw_hash_set.cc

@@ -23,6 +23,8 @@ namespace absl {
 ABSL_NAMESPACE_BEGIN
 namespace container_internal {
 
+// A single block of empty control bytes for tables without any slots allocated.
+// This enables removing a branch in the hot path of find().
 alignas(16) ABSL_CONST_INIT ABSL_DLL const ctrl_t kEmptyGroup[16] = {
     ctrl_t::kSentinel, ctrl_t::kEmpty, ctrl_t::kEmpty, ctrl_t::kEmpty,
     ctrl_t::kEmpty,    ctrl_t::kEmpty, ctrl_t::kEmpty, ctrl_t::kEmpty,

absl/debugging/internal/examine_stack.cc

@@ -20,7 +20,13 @@
 #include <unistd.h>
 #endif
 
-#ifdef __APPLE__
+#include "absl/base/config.h"
+
+#ifdef ABSL_HAVE_MMAP
+#include <sys/mman.h>
+#endif
+
+#if defined(__linux__) || defined(__APPLE__)
 #include <sys/ucontext.h>
 #endif
 
@@ -38,7 +44,102 @@ ABSL_NAMESPACE_BEGIN
 namespace debugging_internal {
 
 namespace {
+constexpr int kDefaultDumpStackFramesLimit = 64;
+// The %p field width for printf() functions is two characters per byte,
+// and two extra for the leading "0x".
+constexpr int kPrintfPointerFieldWidth = 2 + 2 * sizeof(void*);
+
 ABSL_CONST_INIT SymbolizeUrlEmitter debug_stack_trace_hook = nullptr;
+
+// Async-signal safe mmap allocator.
+void* Allocate(size_t num_bytes) {
+#ifdef ABSL_HAVE_MMAP
+  void* p = ::mmap(nullptr, num_bytes, PROT_READ | PROT_WRITE,
+                   MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+  return p == MAP_FAILED ? nullptr : p;
+#else
+  (void)num_bytes;
+  return nullptr;
+#endif  // ABSL_HAVE_MMAP
+}
+
+void Deallocate(void* p, size_t size) {
+#ifdef ABSL_HAVE_MMAP
+  ::munmap(p, size);
+#else
+  (void)p;
+  (void)size;
+#endif  // ABSL_HAVE_MMAP
+}
+
+// Print a program counter only.
+void DumpPC(OutputWriter* writer, void* writer_arg, void* const pc,
+            const char* const prefix) {
+  char buf[100];
+  snprintf(buf, sizeof(buf), "%s@ %*p\n", prefix, kPrintfPointerFieldWidth, pc);
+  writer(buf, writer_arg);
+}
+
+// Print a program counter and the corresponding stack frame size.
+void DumpPCAndFrameSize(OutputWriter* writer, void* writer_arg, void* const pc,
+                        int framesize, const char* const prefix) {
+  char buf[100];
+  if (framesize <= 0) {
+    snprintf(buf, sizeof(buf), "%s@ %*p  (unknown)\n", prefix,
+             kPrintfPointerFieldWidth, pc);
+  } else {
+    snprintf(buf, sizeof(buf), "%s@ %*p  %9d\n", prefix,
+             kPrintfPointerFieldWidth, pc, framesize);
+  }
+  writer(buf, writer_arg);
+}
+
+// Print a program counter and the corresponding symbol.
+void DumpPCAndSymbol(OutputWriter* writer, void* writer_arg, void* const pc,
+                     const char* const prefix) {
+  char tmp[1024];
+  const char* symbol = "(unknown)";
+  // Symbolizes the previous address of pc because pc may be in the
+  // next function.  The overrun happens when the function ends with
+  // a call to a function annotated noreturn (e.g. CHECK).
+  // If symbolization of pc-1 fails, also try pc on the off-chance
+  // that we crashed on the first instruction of a function (that
+  // actually happens very often for e.g. __restore_rt).
+  const uintptr_t prev_pc = reinterpret_cast<uintptr_t>(pc) - 1;
+  if (absl::Symbolize(reinterpret_cast<const char*>(prev_pc), tmp,
+                      sizeof(tmp)) ||
+      absl::Symbolize(pc, tmp, sizeof(tmp))) {
+    symbol = tmp;
+  }
+  char buf[1024];
+  snprintf(buf, sizeof(buf), "%s@ %*p  %s\n", prefix, kPrintfPointerFieldWidth,
+           pc, symbol);
+  writer(buf, writer_arg);
+}
+
+// Print a program counter, its stack frame size, and its symbol name.
+// Note that there is a separate symbolize_pc argument. Return addresses may be
+// at the end of the function, and this allows the caller to back up from pc if
+// appropriate.
+void DumpPCAndFrameSizeAndSymbol(OutputWriter* writer, void* writer_arg,
+                                 void* const pc, void* const symbolize_pc,
+                                 int framesize, const char* const prefix) {
+  char tmp[1024];
+  const char* symbol = "(unknown)";
+  if (absl::Symbolize(symbolize_pc, tmp, sizeof(tmp))) {
+    symbol = tmp;
+  }
+  char buf[1024];
+  if (framesize <= 0) {
+    snprintf(buf, sizeof(buf), "%s@ %*p  (unknown)  %s\n", prefix,
+             kPrintfPointerFieldWidth, pc, symbol);
+  } else {
+    snprintf(buf, sizeof(buf), "%s@ %*p  %9d  %s\n", prefix,
+             kPrintfPointerFieldWidth, pc, framesize, symbol);
+  }
+  writer(buf, writer_arg);
+}
+
 }  // namespace
 
 void RegisterDebugStackTraceHook(SymbolizeUrlEmitter hook) {
@@ -50,7 +151,7 @@ SymbolizeUrlEmitter GetDebugStackTraceHook() { return debug_stack_trace_hook; }
 // Returns the program counter from signal context, nullptr if
 // unknown. vuc is a ucontext_t*. We use void* to avoid the use of
 // ucontext_t on non-POSIX systems.
-void* GetProgramCounter(void* vuc) {
+void* GetProgramCounter(void* const vuc) {
 #ifdef __linux__
   if (vuc != nullptr) {
     ucontext_t* context = reinterpret_cast<ucontext_t*>(vuc);
@@ -132,60 +233,17 @@ void* GetProgramCounter(void* vuc) {
   return nullptr;
 }
 
-// The %p field width for printf() functions is two characters per byte,
-// and two extra for the leading "0x".
-static constexpr int kPrintfPointerFieldWidth = 2 + 2 * sizeof(void*);
-
-// Print a program counter, its stack frame size, and its symbol name.
-// Note that there is a separate symbolize_pc argument. Return addresses may be
-// at the end of the function, and this allows the caller to back up from pc if
-// appropriate.
-static void DumpPCAndFrameSizeAndSymbol(void (*writerfn)(const char*, void*),
-                                        void* writerfn_arg, void* pc,
-                                        void* symbolize_pc, int framesize,
-                                        const char* const prefix) {
-  char tmp[1024];
-  const char* symbol = "(unknown)";
-  if (absl::Symbolize(symbolize_pc, tmp, sizeof(tmp)) ||
-      (pc != symbolize_pc && absl::Symbolize(pc, tmp, sizeof(tmp)))) {
-    symbol = tmp;
-  }
-  char buf[1024];
-  if (framesize <= 0) {
-    snprintf(buf, sizeof(buf), "%s@ %*p  (unknown)  %s\n", prefix,
-             kPrintfPointerFieldWidth, pc, symbol);
-  } else {
-    snprintf(buf, sizeof(buf), "%s@ %*p  %9d  %s\n", prefix,
-             kPrintfPointerFieldWidth, pc, framesize, symbol);
-  }
-  writerfn(buf, writerfn_arg);
-}
-
-// Print a program counter and the corresponding stack frame size.
-static void DumpPCAndFrameSize(void (*writerfn)(const char*, void*),
-                               void* writerfn_arg, void* pc, int framesize,
-                               const char* const prefix) {
-  char buf[100];
-  if (framesize <= 0) {
-    snprintf(buf, sizeof(buf), "%s@ %*p  (unknown)\n", prefix,
-             kPrintfPointerFieldWidth, pc);
-  } else {
-    snprintf(buf, sizeof(buf), "%s@ %*p  %9d\n", prefix,
-             kPrintfPointerFieldWidth, pc, framesize);
-  }
-  writerfn(buf, writerfn_arg);
-}
-
-void DumpPCAndFrameSizesAndStackTrace(
-    void* pc, void* const stack[], int frame_sizes[], int depth,
-    int min_dropped_frames, bool symbolize_stacktrace,
-    void (*writerfn)(const char*, void*), void* writerfn_arg) {
+void DumpPCAndFrameSizesAndStackTrace(void* const pc, void* const stack[],
+                                      int frame_sizes[], int depth,
+                                      int min_dropped_frames,
+                                      bool symbolize_stacktrace,
+                                      OutputWriter* writer, void* writer_arg) {
   if (pc != nullptr) {
     // We don't know the stack frame size for PC, use 0.
     if (symbolize_stacktrace) {
-      DumpPCAndFrameSizeAndSymbol(writerfn, writerfn_arg, pc, pc, 0, "PC: ");
+      DumpPCAndFrameSizeAndSymbol(writer, writer_arg, pc, pc, 0, "PC: ");
     } else {
-      DumpPCAndFrameSize(writerfn, writerfn_arg, pc, 0, "PC: ");
+      DumpPCAndFrameSize(writer, writer_arg, pc, 0, "PC: ");
     }
   }
   for (int i = 0; i < depth; i++) {
@@ -195,20 +253,61 @@ void DumpPCAndFrameSizesAndStackTrace(
       // call to a function annotated noreturn (e.g. CHECK). Note that we don't
       // do this for pc above, as the adjustment is only correct for return
       // addresses.
-      DumpPCAndFrameSizeAndSymbol(writerfn, writerfn_arg, stack[i],
+      DumpPCAndFrameSizeAndSymbol(writer, writer_arg, stack[i],
                                   reinterpret_cast<char*>(stack[i]) - 1,
                                   frame_sizes[i], "    ");
     } else {
-      DumpPCAndFrameSize(writerfn, writerfn_arg, stack[i], frame_sizes[i],
-                         "    ");
+      DumpPCAndFrameSize(writer, writer_arg, stack[i], frame_sizes[i], "    ");
     }
   }
   if (min_dropped_frames > 0) {
     char buf[100];
     snprintf(buf, sizeof(buf), "    @ ... and at least %d more frames\n",
              min_dropped_frames);
-    writerfn(buf, writerfn_arg);
+    writer(buf, writer_arg);
+  }
+}
+
+// Dump current stack trace as directed by writer.
+// Make sure this function is not inlined to avoid skipping too many top frames.
+ABSL_ATTRIBUTE_NOINLINE
+void DumpStackTrace(int min_dropped_frames, int max_num_frames,
+                    bool symbolize_stacktrace, OutputWriter* writer,
+                    void* writer_arg) {
+  // Print stack trace
+  void* stack_buf[kDefaultDumpStackFramesLimit];
+  void** stack = stack_buf;
+  int num_stack = kDefaultDumpStackFramesLimit;
+  int allocated_bytes = 0;
+
+  if (num_stack >= max_num_frames) {
+    // User requested fewer frames than we already have space for.
+    num_stack = max_num_frames;
+  } else {
+    const size_t needed_bytes = max_num_frames * sizeof(stack[0]);
+    void* p = Allocate(needed_bytes);
+    if (p != nullptr) {  // We got the space.
+      num_stack = max_num_frames;
+      stack = reinterpret_cast<void**>(p);
+      allocated_bytes = needed_bytes;
+    }
+  }
+
+  size_t depth = absl::GetStackTrace(stack, num_stack, min_dropped_frames + 1);
+  for (size_t i = 0; i < depth; i++) {
+    if (symbolize_stacktrace) {
+      DumpPCAndSymbol(writer, writer_arg, stack[i], "    ");
+    } else {
+      DumpPC(writer, writer_arg, stack[i], "    ");
+    }
   }
+
+  auto hook = GetDebugStackTraceHook();
+  if (hook != nullptr) {
+    (*hook)(stack, depth, writer, writer_arg);
+  }
+
+  if (allocated_bytes != 0) Deallocate(stack, allocated_bytes);
 }
 
 }  // namespace debugging_internal

absl/debugging/internal/examine_stack.h

@@ -31,7 +31,7 @@ typedef void OutputWriter(const char*, void*);
 // `hook` that is called each time DumpStackTrace() is called.
 // `hook` may be called from a signal handler.
 typedef void (*SymbolizeUrlEmitter)(void* const stack[], int depth,
-                                    OutputWriter writer, void* writer_arg);
+                                    OutputWriter* writer, void* writer_arg);
 
 // Registration of SymbolizeUrlEmitter for use inside of a signal handler.
 // This is inherently unsafe and must be signal safe code.
@@ -41,14 +41,21 @@ SymbolizeUrlEmitter GetDebugStackTraceHook();
 // Returns the program counter from signal context, or nullptr if
 // unknown. `vuc` is a ucontext_t*. We use void* to avoid the use of
 // ucontext_t on non-POSIX systems.
-void* GetProgramCounter(void* vuc);
+void* GetProgramCounter(void* const vuc);
 
-// Uses `writerfn` to dump the program counter, stack trace, and stack
+// Uses `writer` to dump the program counter, stack trace, and stack
 // frame sizes.
-void DumpPCAndFrameSizesAndStackTrace(
-    void* pc, void* const stack[], int frame_sizes[], int depth,
-    int min_dropped_frames, bool symbolize_stacktrace,
-    void (*writerfn)(const char*, void*), void* writerfn_arg);
+void DumpPCAndFrameSizesAndStackTrace(void* const pc, void* const stack[],
+                                      int frame_sizes[], int depth,
+                                      int min_dropped_frames,
+                                      bool symbolize_stacktrace,
+                                      OutputWriter* writer, void* writer_arg);
+
+// Dump current stack trace omitting the topmost `min_dropped_frames` stack
+// frames.
+void DumpStackTrace(int min_dropped_frames, int max_num_frames,
+                    bool symbolize_stacktrace, OutputWriter* writer,
+                    void* writer_arg);
 
 }  // namespace debugging_internal
 ABSL_NAMESPACE_END