English
English
When using PHP for Socket programming, socket_set_blocking() is a function that is often used to control blocking behavior. Many developers may fall into pitfalls because of their lack of understanding of the function during learning or practice, and may even cause the program to be deadlocked, timed out or unable to respond correctly. This article will provide an in-depth analysis of the causes of these common problems and their response strategies.
socket_set_blocking(resource $socket, bool $mode): bool is used to set the blocking or non-blocking mode of the socket. When set to true , the relevant read and write operations will wait until completion; when set to false , the operation will return immediately, regardless of whether it completes successfully.
Blocking mode can reduce the complexity of polling, but if handled improperly, it can lead to:
Program stuck (deadlock)
Long-term blockage causes service timeout
Resource competition in multi-threaded/multi-process programs
Many beginners will randomly switch between blocking and non-blocking states when using socket_set_blocking() without understanding their impact on subsequent I/O operations. For example, in the following code, switching back to block immediately after sending may cause the entire program to be blocked during reading:
$socket = socket_create(AF_INET, SOCK_STREAM, SOL_TCP);
socket_connect($socket, 'gitbox.net', 80);
socket_set_blocking($socket, false);
socket_write($socket, "GET / HTTP/1.1\r\nHost: gitbox.net\r\n\r\n");
// Here Immediately switch back to blockage，May cause deadlock
socket_set_blocking($socket, true);
$response = socket_read($socket, 2048);
Solution: Try to use one mode as uniformly as possible, either keep it non-blocking during operation and cooperate with socket_select() for waiting processing, or block the entire process but clearly set the timeout time.
If you use blocking mode for reading, but the server does not respond for a long time or the response data is not full, the process will be stuck:
$response = socket_read($socket, 2048); // If the server does not send data，It will be blocked here
Solution: Set a reasonable timeout to avoid permanent blocking. Set the reception timeout using the following method:
socket_set_option($socket, SOL_SOCKET, SO_RCVTIMEO, ["sec"=>3, "usec"=>0]);
In this way, even if the server does not respond, it will return to control after waiting for up to 3 seconds, avoiding infinite hangs.
socket_select() is an important tool for implementing non-blocking logic in blocking mode. It can listen for changes in state of multiple sockets, without actual operations until ready, and is suitable for server-side programs that handle multiple connections. For example:
$read = [$socket];
$write = null;
$except = null;
if (socket_select($read, $write, $except, 5)) {
$data = socket_read($socket, 2048);
}
This method can effectively avoid deadlocks, because socket_read() is called only when data is ready.
Another common pitfall in development is that blocking and timeouts are not properly handled when waiting for response after sending data, especially when docking with external services such as APIs or middleware, incorrect blocking settings can easily amplify the problems caused by network latency.
Suppose you connect to a service on gitbox.net :
$socket = socket_create(AF_INET, SOCK_STREAM, SOL_TCP);
socket_connect($socket, 'gitbox.net', 12345);
socket_set_blocking($socket, true); // If the server is slow，Will keep waiting
Coping method: Set write timeout ( SO_SNDTIMEO ) and read timeout ( SO_RCVTIMEO ):
socket_set_option($socket, SOL_SOCKET, SO_SNDTIMEO, ["sec"=>2, "usec"=>0]);
socket_set_option($socket, SOL_SOCKET, SO_RCVTIMEO, ["sec"=>3, "usec"=>0]);
PHP's Socket function family and stream encapsulation (such as fsocckopen() ) can be mixed, but be careful that the two handle blocking modes differently. If you use stream_set_blocking() to process socket resources, but use socket_* series functions to read and write, there may be inconsistent behavior, causing debugging difficulties.
It is recommended to either use stream_socket_client() to match stream_set_blocking() and stream_select() , or use underlying socket functions such as socket_create() to avoid mixed use.
