运行环境:
- Linux 4.x
- async-profiler 1.6 (https://github.com/jvm-profiling-tools/async-profiler)
- OpenJDK8
应用程序代码:
通过 SocketInputStream 进行域套接字通信
操作:
使用 async profiler 运行应用程序: -d 60 -e alloc -f /tmp/alloc.svg
问题:
从 SocketInputStream#socketRead0 意外分配了字符串
(青色: TLAB 分配)
socketRead 和 socketRead0 的 JDK 代码
private int socketRead(FileDescriptor fd,
byte b[], int off, int len,
int timeout)
throws IOException {
return socketRead0(fd, b, off, len, timeout);
}
private native int socketRead0(FileDescriptor fd,
byte b[], int off, int len,
int timeout)
本地Socket实现:
- jdk/src/solaris/native/java/net/SocketInputStream.c
假设:
在以下代码中,字符串可能是通过JNI在java堆中分配的,因为在字符串分配旁边的StackTrace中有一个SocketTimeoutException。
Java_java_net_SocketInputStream_socketRead0(JNIEnv *env, jobject this,
jobject fdObj, jbyteArray data,
jint off, jint len, jint timeout)
{
[...]
if (timeout) {
nread = NET_ReadWithTimeout(env, fd, bufP, len, timeout);
if ((*env)->ExceptionCheck(env)) {
if (bufP != BUF) {
free(bufP);
}
return nread;
}
} else {
nread = NET_Read(fd, bufP, len);
}
[...]
}
static int NET_ReadWithTimeout(JNIEnv *env, int fd, char *bufP, int len, long timeout) {
int result = 0;
long prevtime = NET_GetCurrentTime(), newtime;
while (timeout > 0) {
result = NET_TimeoutWithCurrentTime(fd, timeout, prevtime);
if (result <= 0) {
if (result == 0) {
JNU_ThrowByName(env, "java/net/SocketTimeoutException", "Read timed out");
} else if (result == -1) {
if (errno == EBADF) {
JNU_ThrowByName(env, "java/net/SocketException", "Socket closed");
} else if (errno == ENOMEM) {
JNU_ThrowOutOfMemoryError(env, "NET_Timeout native heap allocation failed");
} else {
JNU_ThrowByNameWithMessageAndLastError
(env, "java/net/SocketException", "select/poll failed");
}
}
return -1;
}
result = NET_NonBlockingRead(fd, bufP, len);
if (result == -1 && ((errno == EAGAIN) || (errno == EWOULDBLOCK))) {
newtime = NET_GetCurrentTime();
timeout -= newtime - prevtime;
if (timeout > 0) {
prevtime = newtime;
}
} else {
break;
}
}
return result;
}
我查看了C代码,没有找到任何jString分配,因此我有点困惑。
有人知道字符串分配可能发生在哪里吗?