GPU/CPU Memory Access Sync (C/C++)

Overview

NativeFence is a module that manages the sync status of fenceFd. You can use the APIs to set the blocking time, block fenceFd permanently, close fenceFd, and check the validity of fenceFd.

Available APIs

Name	Description
OH_NativeFence_IsValid (int fenceFd)	Checks whether fenceFd is valid.
OH_NativeFence_Wait (int fenceFd, uint32_t timeout)	Blocks the input fenceFd. The timeout parameter specifies the maximum waiting time.
OH_NativeFence_WaitForever (int fenceFd)	Permanently blocks the input fenceFd.
OH_NativeFence_Close (int fenceFd)	Closes fenceFd.

For details about the APIs, see NativeFence.

How to Develop

The following describes how to use the native APIs provided by NativeFence.

Adding Dynamic Link Libraries

Add the following library file to the CMakeLists.txt file.

libnative_fence.so

Header Files

#include <native_fence/native_fence.h>
#include <cstring>
#include <iostream>
#include <linux/sync_file.h>
#include <signal.h>
#include <sys/signalfd.h>
#include <unistd.h>

1. Call signalfd() to create fenceFd.

   sigset_t mask;
   sigemptyset(&mask);
   sigaddset(&mask, SIGINT); // Monitor SIGINT signal (Ctrl C)
   sigaddset(&mask, SIGURG); // Generated when urgent data or out of band data arrives at the socket
   sigprocmask(SIG_BLOCK, &mask, NULL);
   int sfd = signalfd(-1, &mask, 0);
   

   napi_init.cpp

2. Check whether the input fenceFd is valid.

   bool isValid = OH_NativeFence_IsValid(INVALID_FD);
   if (!isValid) {
       DRAWING_LOGW("fenceFd is invalid");
   }
   

   napi_init.cpp

3. Call the OH_NativeFence_Wait blocking API to wait for the fence to complete and then perform the next operation.

   constexpr uint32_t TIMEOUT_MS = 5000;
   // ···
   bool result = OH_NativeFence_Wait(INVALID_FD, TIMEOUT_MS);
   

   napi_init.cpp

4. Call the OH_NativeFence_WaitForever blocking API to wait for the fence to complete and then perform the next operation.

   bool result2 = false;
   auto startTime = std::chrono::steady_clock::now();
   result2 = OH_NativeFence_WaitForever(sfd);
   auto endTime = std::chrono::steady_clock::now();
   auto duration = std::chrono::duration_cast<std::chrono::milliseconds>(endTime - startTime).count();
   if (result2) {
       DRAWING_LOGI("SyncFenceWaitForever has an event occurring result2 %{public}d, cost_time: %{public}d",
           result2, duration);
   } else {
       DRAWING_LOGI("SyncFenceWaitForever timeout with no event occurrence"
           "result2 %{public}d, cost_time: %{public}d", result2, duration);
   }
   

   napi_init.cpp

5. The GPU or CPU sends a sync signal to notify fenceFd of unblocking.

6. Close fenceFd.

   OH_NativeFence_Close(sfd);
   

   napi_init.cpp