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正如@Elviss提到的-
将代码发布到主线程中,您应该使用Looper。实际上,无需额外处理JNI以及创建自定义项java.lang.Runnable并通过复杂的JNI内容将其发布即可完成此操作。
Android
NDK提供了极其轻便高效的方式来将本机代码发布到任意循环程序。关键是您应该向循环程序提供任意文件描述符,并指定您感兴趣的文件事件(输入,输出等)。在后台,looper会轮询该文件描述符,一旦事件可用,它将在适当的线程上运行您的回调。
有一个最小的示例(没有错误检查和删除):
#include
#include
#define LOGI(...) __android_log_print(ANDROID_LOG_INFO, "sergik", __VA_ARGS__)
static ALooper* mainThreadLooper;
static int messagePipe[2];
static int looperCallback(int fd, int events, void* data);
void someJniFuncThatYouShouldCallOnceOnMainThread() {
mainThreadLooper = ALooper_forThread(); // get looper for this thread
ALooper_acquire(mainThreadLooper); // add reference to keep object alive
pipe(messagePipe); //create send-receive pipe
// listen for pipe read end, if there is something to read
// - notify via provided callback on main thread
ALooper_addFd(mainThreadLooper, messagePipe[0],
0, ALOOPER_EVENT_INPUT, looperCallback, nullptr);
LOGI("fd is registered");
// send few messages from arbitrary thread
std::thread worker([]() {
for(char msg = 100; msg < 110; msg++) {
LOGI("send message #%d", msg);
write(messagePipe[1], &msg, 1);
sleep(1);
}
});
worker.detach();
}
// this will be called on main thread
static int looperCallback(int fd, int events, void* data) {
char msg;
read(fd, &msg, 1); // read message from pipe
LOGI("got message #%d", msg);
return 1; // continue listening for events
}
此代码产生下一个输出:
06-28 23:28:27.076 30930-30930/? I/sergik: fd is registered
06-28 23:28:27.076 30930-30945/? I/sergik: send message #100
06-28 23:28:27.089 30930-30930/? I/sergik: got message #100
06-28 23:28:28.077 30930-30945/? I/sergik: send message #101
06-28 23:28:28.077 30930-30930/? I/sergik: got message #101
06-28 23:28:29.077 30930-30945/? I/sergik: send message #102
06-28 23:28:29.078 30930-30930/? I/sergik: got message #102
06-28 23:28:30.078 30930-30945/? I/sergik: send message #103
06-28 23:28:30.078 30930-30930/? I/sergik: got message #103
06-28 23:28:31.079 30930-30945/? I/sergik: send message #104
06-28 23:28:31.079 30930-30930/? I/sergik: got message #104
06-28 23:28:32.079 30930-30945/? I/sergik: send message #105
06-28 23:28:32.080 30930-30930/? I/sergik: got message #105
06-28 23:28:33.080 30930-30945/? I/sergik: send message #106
06-28 23:28:33.080 30930-30930/? I/sergik: got message #106
06-28 23:28:34.081 30930-30945/? I/sergik: send message #107
06-28 23:28:34.081 30930-30930/? I/sergik: got message #107
06-28 23:28:35.081 30930-30945/? I/sergik: send message #108
06-28 23:28:35.082 30930-30930/? I/sergik: got message #108
06-28 23:28:36.082 30930-30945/? I/sergik: send message #109
06-28 23:28:36.083 30930-30930/? I/sergik: got message #109
从pid-tid对中可以看到-消息是在主线程上接收的。当然,您可能会发送比一字节消息更复杂的内容。
2020-10-09
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