[openmp] Do not use shared memory on Android

[pirama]

Summary

Android provides ashmem/ASharedMemory support on newer releases, which
we can use if requested by openmp users on Android.

[pirama]

I uploaded this as a starter but we should abstract the check to avoid repetition. Is kmp_config.h.cmake or kmp_platform.h a good place for defining a 'KMP_USE_SHMEM' and using it here?

Also, I added reviewers based on arc cover. Please add other relevant reviewers.

[pirama]

Refactor preprocessor check to kmp_config.h.

[AndreyChurbanov]

LGTM

openmp/runtime/src/kmp_config.h.cmake

 
 #if KMP_OS_WINDOWS
 # define KMP_WIN_CDECL
 #else
 # define BUILD_TV
 # define KMP_GOMP_COMPAT
 #endif
 
+// use shared memory with dynamic library (except Android, where shm_*
+// functions don't exist).
+#if KMP_OS_UNIX && KMP_DYNAMIC_LIB && !__ANDROID__
+#define KMP_USE_SHM
+#endif
 #endif // KMP_CONFIG_H

openmp/runtime/src/kmp_runtime.cpp

#endif
 
   KA_TRACE(50, ("__kmp_register_library_startup: %s=\"%s\"\n", name,
                 __kmp_registration_str));
 
   while (!done) {
 
     char *value = NULL; // Actual value of the environment variable.
 
-#if KMP_OS_UNIX && KMP_DYNAMIC_LIB // shared memory is with dynamic library
+#if defined(KMP_USE_SHM)
     char *shm_name = __kmp_str_format("/%s", name);
     int shm_preexist = 0;
     char *data1;
     int fd1 = shm_open(shm_name, O_CREAT | O_EXCL | O_RDWR, 0666);
     if ((fd1 == -1) && (errno == EEXIST)) {
       // file didn't open because it already exists.
       // try opening existing file
       fd1 = shm_open(shm_name, O_RDWR, 0666);
if (value != NULL && strcmp(value, __kmp_registration_str) == 0) {
                       KMP_HNT(DuplicateLibrary), __kmp_msg_null);
         }
         KMP_INTERNAL_FREE(duplicate_ok);
         __kmp_duplicate_library_ok = 1;
         done = 1; // Exit the loop.
       } break;
       case 2: { // Neighbor is dead.
 
-#if KMP_OS_UNIX && KMP_DYNAMIC_LIB // shared memory is with dynamic library
+#if defined(KMP_USE_SHM)
         // close shared memory.
         shm_unlink(shm_name); // this removes file in /dev/shm
 #else
         // Clear the variable and try to register library again.
         __kmp_env_unset(name);
 #endif
       } break;
       default: {
         KMP_DEBUG_ASSERT(0);
       } break;
       }
     }
     KMP_INTERNAL_FREE((void *)value);
-#if KMP_OS_UNIX && KMP_DYNAMIC_LIB // shared memory is with dynamic library
+#if defined(KMP_USE_SHM)
     KMP_INTERNAL_FREE((void *)shm_name);
 #endif
   } // while
   KMP_INTERNAL_FREE((void *)name);
 
 } // func __kmp_register_library_startup
 
 void __kmp_unregister_library(void) {
 
   char *name = __kmp_reg_status_name();
   char *value = NULL;
 
-#if KMP_OS_UNIX && KMP_DYNAMIC_LIB // shared memory is with dynamic library
+#if defined(KMP_USE_SHM)
   char *shm_name = __kmp_str_format("/%s", name);
   int fd1 = shm_open(shm_name, O_RDONLY, 0666);
   if (fd1 == -1) {
     // file did not open. return.
     return;
   }
   char *data1 = (char *)mmap(0, SHM_SIZE, PROT_READ, MAP_SHARED, fd1, 0);
   if (data1 != MAP_FAILED) {
     value = __kmp_str_format("%s", data1); // read value from SHM
     munmap(data1, SHM_SIZE);
   }
   close(fd1);
 #else
   value = __kmp_env_get(name);
 #endif
 
   KMP_DEBUG_ASSERT(__kmp_registration_flag != 0);
   KMP_DEBUG_ASSERT(__kmp_registration_str != NULL);
   if (value != NULL && strcmp(value, __kmp_registration_str) == 0) {
 //  Ok, this is our variable. Delete it.
-#if KMP_OS_UNIX && KMP_DYNAMIC_LIB // shared memory is with dynamic library
+#if defined(KMP_USE_SHM)
     shm_unlink(shm_name); // this removes file in /dev/shm
 #else
     __kmp_env_unset(name);
 #endif
   }
 
-#if KMP_OS_UNIX && KMP_DYNAMIC_LIB // shared memory is with dynamic library
+#if defined(KMP_USE_SHM)
   KMP_INTERNAL_FREE(shm_name);
 #endif
 
   KMP_INTERNAL_FREE(__kmp_registration_str);
   KMP_INTERNAL_FREE(value);
   KMP_INTERNAL_FREE(name);
 
   __kmp_registration_flag = 0;