[SERVER] Make signal handling more POSIX

According to POSIX, a signal sent to a PID can be delivered to an
arbitrary thread of that process that hasn't the signal blocked. This
seens to never happen on Linux, but would mess things up since the code
expected the main signal handler to only be executed by the main thread.
This should now be fixed by examining the destination PID of the signal
as well as the ID of the thread currently running the signal handler. If
we notice the signal wasn't sent by our own PID and the handler is not
currently run by the main thread, we re-send the signal to the main
thread. Otherwise, if the signal was sent by our own PID but the handler
is not run in the main thread, do nothing. This way we can use
pthread_kill() to wake up threads that might be stuck in a blocking
syscall when it's time to shut down.

1 files changed, 8 insertions, 5 deletions

diff --git a/src/server/rpc.c b/src/server/rpc.c
index 261c6c0..662263e 100644
--- a/src/server/rpc.c
+++ b/src/server/rpc.c
@@ -137,13 +137,13 @@ void rpc_sendStatsJson(int sock, dnbd3_host_t* host, const void* data, const int
 	bool hasName = false;
 	bool ok;
 	int keepAlive = HTTP_KEEPALIVE;
-	do {
+	while ( !_shutdown ) {
 		// Read request from client
 		struct phr_header headers[100];
 		size_t numHeaders, prevLen = 0, consumed;
 		struct string method, path;
 		int minorVersion;
-		do {
+		while ( !_shutdown ) {
 			// Parse before calling recv, there might be a complete pipelined request in the buffer already
 			// If the request is incomplete, we allow exactly one additional recv() to complete it.
 			// This should suffice for real world scenarios as I don't know of any
@@ -188,7 +188,9 @@ void rpc_sendStatsJson(int sock, dnbd3_host_t* host, const void* data, const int
 				sendReply( sock, "400 Bad Request", "text/plain", "Server cannot understand what you're trying to say", -1, HTTP_CLOSE );
 				goto func_return;
 			}
-		} while ( true );
+		} // Loop while request header incomplete
+		if ( _shutdown )
+			break;
 		if ( keepAlive == HTTP_KEEPALIVE ) {
 			// Only keep the connection alive (and indicate so) if the client seems to support this
 			if ( minorVersion == 0 || hasHeaderValue( headers, numHeaders, &STR_CONNECTION, &STR_CLOSE ) ) {
@@ -213,7 +215,8 @@ void rpc_sendStatsJson(int sock, dnbd3_host_t* host, const void* data, const int
 			} else {
 				ok = sendReply( sock, "404 Not found", "text/plain", "Nothing", -1, keepAlive );
 			}
-			if ( !ok ) break;
+			if ( !ok )
+				break;
 		}
 		// hoff might be beyond end if the client sent another request (burst)
 		const ssize_t extra = hoff - consumed;
@@ -225,7 +228,7 @@ void rpc_sendStatsJson(int sock, dnbd3_host_t* host, const void* data, const int
 			hasName = true;
 			setThreadName( "HTTP" );
 		}
-	} while (true);
+	} // Loop while more requests
 func_return:;
 	do {
 		const int curCount = --status.count;