[PATCH spice-streaming-agent 9/9] Refactor and simplify polling for messages to read

[Lukáš Hrázký <lhrazky@xxxxxxxxxx>]

Use exceptions for errors, remove the inner loop in read_command, which
should practically never do more than one iteration. Handle EINTR from
poll and report nothing to read, relying on the enclosing loop to poll
for the command on the next iteration.

Signed-off-by: Lukáš Hrázký <lhrazky@xxxxxxxxxx>
---
 src/spice-streaming-agent.cpp | 40 ++++++++++++++--------------------------
 1 file changed, 14 insertions(+), 26 deletions(-)

diff --git a/src/spice-streaming-agent.cpp b/src/spice-streaming-agent.cpp
index 2fdd02f..9674262 100644
--- a/src/spice-streaming-agent.cpp
+++ b/src/spice-streaming-agent.cpp
@@ -60,20 +60,24 @@ static bool quit_requested = false;
 static bool log_binary = false;
 static std::set<SpiceVideoCodecType> client_codecs;
 
-static int have_something_to_read(StreamPort &stream_port, int timeout)
+static bool have_something_to_read(StreamPort &stream_port, bool blocking)
 {
     struct pollfd pollfd = {stream_port.fd, POLLIN, 0};
 
-    if (poll(&pollfd, 1, timeout) < 0) {
-        syslog(LOG_ERR, "poll FAILED\n");
-        return -1;
+    if (poll(&pollfd, 1, blocking ? -1 : 0) < 0) {
+        if (errno == EINTR) {
+            // report nothing to read, next iteration of the enclosing loop will retry
+            return false;
+        }
+
+        throw IOError("poll failed on the device", errno);
     }
 
     if (pollfd.revents & POLLIN) {
-        return 1;
+        return true;
     }
 
-    return 0;
+    return false;
 }
 
 static void handle_stream_start_stop(StreamPort &stream_port, uint32_t len)
@@ -162,22 +166,11 @@ static void read_command_from_device(StreamPort &stream_port)
     throw std::runtime_error("UNKNOWN msg of type " + std::to_string(hdr.type));
 }
 
-static int read_command(StreamPort &stream_port, bool blocking)
+static void read_command(StreamPort &stream_port, bool blocking)
 {
-    int timeout = blocking?-1:0;
-    while (!quit_requested) {
-        if (!have_something_to_read(stream_port, timeout)) {
-            if (!blocking) {
-                return 0;
-            }
-            sleep(1);
-            continue;
-        }
+    if (have_something_to_read(stream_port, blocking)) {
         read_command_from_device(stream_port);
-        break;
     }
-
-    return 1;
 }
 
 static void spice_stream_send_format(StreamPort &stream_port, unsigned w, unsigned h, unsigned c)
@@ -325,9 +318,7 @@ do_capture(StreamPort &stream_port, FILE *f_log)
     unsigned int frame_count = 0;
     while (!quit_requested) {
         while (!quit_requested && !streaming_requested) {
-            if (read_command(stream_port, true) < 0) {
-                throw std::runtime_error("FAILED to read command");
-            }
+            read_command(stream_port, true);
         }
 
         if (quit_requested) {
@@ -388,10 +379,7 @@ do_capture(StreamPort &stream_port, FILE *f_log)
                 break;
             }
 
-            //usleep(1);
-            if (read_command(stream_port, false) < 0) {
-                throw std::runtime_error("FAILED to read command");
-            }
+            read_command(stream_port, false);
         }
     }
 }
-- 
2.16.2

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