Export of internal Abseil changes.

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821196cfb2a3b943ffdc4c9e75daec92d7ffb28b by Abseil Team <absl-team@google.com>:

Performance improvements

PiperOrigin-RevId: 212668992

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704858e2e767016bad27d53eec01d9d48e546b23 by Abseil Team <absl-team@google.com>:

Low-level Portability enchancements for Abseil Mutex on WebAssembly.

Emscripten Pthreads do not use signals, so remove use of pthread_sigmask or
other async-signal-safe related handling code.

PiperOrigin-RevId: 212527958

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be3e38cb4d493b755132d20c8c2d1a51e45d5449 by Jon Cohen <cohenjon@google.com>:

Internal change.

PiperOrigin-RevId: 212523797
GitOrigin-RevId: 821196cfb2a3b943ffdc4c9e75daec92d7ffb28b
Change-Id: I5694e23e4e09364a15dd6fc4e2e3f15e38835687

3 files changed, 27 insertions, 4 deletions

diff --git a/absl/base/internal/low_level_alloc.cc b/absl/base/internal/low_level_alloc.cc
index 0a6f3070..6e636a02 100644
--- a/absl/base/internal/low_level_alloc.cc
+++ b/absl/base/internal/low_level_alloc.cc
@@ -401,16 +401,20 @@ bool LowLevelAlloc::DeleteArena(Arena *arena) {
     ABSL_RAW_CHECK(munmap_result != 0,
                    "LowLevelAlloc::DeleteArena: VitualFree failed");
 #else
+#ifndef ABSL_LOW_LEVEL_ALLOC_ASYNC_SIGNAL_SAFE_MISSING
     if ((arena->flags & LowLevelAlloc::kAsyncSignalSafe) == 0) {
       munmap_result = munmap(region, size);
     } else {
       munmap_result = base_internal::DirectMunmap(region, size);
     }
+#else
+    munmap_result = munmap(region, size);
+#endif  // ABSL_LOW_LEVEL_ALLOC_ASYNC_SIGNAL_SAFE_MISSING
     if (munmap_result != 0) {
       ABSL_RAW_LOG(FATAL, "LowLevelAlloc::DeleteArena: munmap failed: %d",
                    errno);
     }
-#endif
+#endif  // _WIN32
   }
   section.Leave();
   arena->~Arena();
@@ -545,6 +549,7 @@ static void *DoAllocWithArena(size_t request, LowLevelAlloc::Arena *arena) {
                                MEM_RESERVE | MEM_COMMIT, PAGE_READWRITE);
       ABSL_RAW_CHECK(new_pages != nullptr, "VirtualAlloc failed");
 #else
+#ifndef ABSL_LOW_LEVEL_ALLOC_ASYNC_SIGNAL_SAFE_MISSING
       if ((arena->flags & LowLevelAlloc::kAsyncSignalSafe) != 0) {
         new_pages = base_internal::DirectMmap(nullptr, new_pages_size,
             PROT_WRITE|PROT_READ, MAP_ANONYMOUS|MAP_PRIVATE, -1, 0);
@@ -552,10 +557,15 @@ static void *DoAllocWithArena(size_t request, LowLevelAlloc::Arena *arena) {
         new_pages = mmap(nullptr, new_pages_size, PROT_WRITE | PROT_READ,
                          MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
       }
+#else
+      new_pages = mmap(nullptr, new_pages_size, PROT_WRITE | PROT_READ,
+                       MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
+#endif  // ABSL_LOW_LEVEL_ALLOC_ASYNC_SIGNAL_SAFE_MISSING
       if (new_pages == MAP_FAILED) {
         ABSL_RAW_LOG(FATAL, "mmap error: %d", errno);
       }
-#endif
+
+#endif  // _WIN32
       arena->mu.Lock();
       s = reinterpret_cast<AllocList *>(new_pages);
       s->header.size = new_pages_size;
diff --git a/absl/base/internal/low_level_alloc.h b/absl/base/internal/low_level_alloc.h
index 3c15605b..fba9466a 100644
--- a/absl/base/internal/low_level_alloc.h
+++ b/absl/base/internal/low_level_alloc.h
@@ -39,10 +39,13 @@
 #define ABSL_LOW_LEVEL_ALLOC_MISSING 1
 #endif
 
-// Using LowLevelAlloc with kAsyncSignalSafe isn't supported on Windows.
+// Using LowLevelAlloc with kAsyncSignalSafe isn't supported on Windows or
+// asm.js / WebAssembly.
+// See https://kripken.github.io/emscripten-site/docs/porting/pthreads.html
+// for more information.
 #ifdef ABSL_LOW_LEVEL_ALLOC_ASYNC_SIGNAL_SAFE_MISSING
 #error ABSL_LOW_LEVEL_ALLOC_ASYNC_SIGNAL_SAFE_MISSING cannot be directly set
-#elif defined(_WIN32)
+#elif defined(_WIN32) || defined(__asmjs__) || defined(__wasm__)
 #define ABSL_LOW_LEVEL_ALLOC_ASYNC_SIGNAL_SAFE_MISSING 1
 #endif
 
diff --git a/absl/base/internal/thread_identity.cc b/absl/base/internal/thread_identity.cc
index 678e8568..cff9c1b4 100644
--- a/absl/base/internal/thread_identity.cc
+++ b/absl/base/internal/thread_identity.cc
@@ -68,6 +68,14 @@ void SetCurrentThreadIdentity(
   // NOTE: Not async-safe.  But can be open-coded.
   absl::call_once(init_thread_identity_key_once, AllocateThreadIdentityKey,
                   reclaimer);
+
+#ifdef __EMSCRIPTEN__
+  // Emscripten PThread implementation does not support signals.
+  // See https://kripken.github.io/emscripten-site/docs/porting/pthreads.html
+  // for more information.
+  pthread_setspecific(thread_identity_pthread_key,
+                      reinterpret_cast<void*>(identity));
+#else
   // We must mask signals around the call to setspecific as with current glibc,
   // a concurrent getspecific (needed for GetCurrentThreadIdentityIfPresent())
   // may zero our value.
@@ -81,6 +89,8 @@ void SetCurrentThreadIdentity(
   pthread_setspecific(thread_identity_pthread_key,
                       reinterpret_cast<void*>(identity));
   pthread_sigmask(SIG_SETMASK, &curr_signals, nullptr);
+#endif  // !__EMSCRIPTEN__
+
 #elif ABSL_THREAD_IDENTITY_MODE == ABSL_THREAD_IDENTITY_MODE_USE_TLS
   // NOTE: Not async-safe.  But can be open-coded.
   absl::call_once(init_thread_identity_key_once, AllocateThreadIdentityKey,