static size_t php_curl_stream_read(php_stream *stream, char *buf, size_t count TSRMLS_DC) { php_curl_stream *curlstream = (php_curl_stream *) stream->abstract; size_t didread = 0; if (curlstream->readbuffer.readpos >= curlstream->readbuffer.writepos && curlstream->pending) { //········ do { /* get the descriptors from curl */ curl_multi_fdset(curlstream->multi, &curlstream->readfds, &curlstream->writefds, &curlstream->excfds, &curlstream->maxfd); /* if we are in blocking mode, set a timeout */ tv.tv_usec = 0; tv.tv_sec = 15; /* TODO: allow this to be configured from the script */ /* wait for data */ switch (select(curlstream->maxfd + 1, &curlstream->readfds, &curlstream->writefds, &curlstream->excfds, &tv)) { case -1: /* error */ return 0; case 0: /* no data yet: timed-out */ return 0; default: /* fetch the data */ do { curlstream->mcode = curl_multi_perform(curlstream->multi, &curlstream->pending); } while (curlstream->mcode == CURLM_CALL_MULTI_PERFORM); } } while (curlstream->readbuffer.readpos >= curlstream->readbuffer.writepos && curlstream->pending > 0); } //·········· return didread; }
GDB进去发现，代码一直在里面的do-while里面循环了！心想curl_multi_fdset怎么不用先FD_ZERO 清空FD呢？一般做法都是会先清空的。
莫非是PHP的bug, 于是网上找了一下发现了这个Pierrick-Charron的commit，确实是一个bug, 其实curl_multi_fdset 的文档开头写了的：
复制代码 代码如下:
This function extracts file descriptor information from a given multi_handle. libcurl returns its fd_set sets. The application can use these to select() on, but be sure to FD_ZERO them before calling this function as curl_multi_fdset(3) only adds its own descriptors,
好吧，最后用GDB验证一下，我在上面的do下面，curl_multi_fdset调用之前，手动将fd清空，看看能否退出循环：
(gdb) print FD_ZERO(&curlstream->readfds)
No symbol “FD_ZERO” in current context.
FD_ZERO竟然没有，不管了，其本来是个宏定义，展开就行：#define FD_ZERO(p) bzero((char *)(p), sizeof(*(p)))
直接用call修改curl_muti_fdset的三个参数数组如下：
复制代码 代码如下:
(gdb) call bzero((char *)(&curlstream->readfds), sizeof(*(&curlstream->readfds)))
$5 = 17055392
(gdb) call bzero((char *)(&curlstream->writefds),sizeof(*(&curlstream->writefds)))
$6 = 17055520
(gdb) call bzero((char *)(&curlstream->excfds), sizeof(*(&curlstream->excfds)))
$7 = 17055648
然后GDB单步执行，如期的由于curlstream->pending变为0，从而退出了循环，回到php_stream_fill_read_buffer的大函数了
到此基本结束。有问题的PHP版本应该是5.2. 具体没有细看，读者可以参考下上面的这个提交改动或者直接看自己的版本代码是否有问题。
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