Add acksync helper to wait for acks

This will allow to send requests with sequence numbers to the server
and wait for acknowledgements.

PR #2814 <https://github.com/Genymobile/scrcpy/pull/2814>

app/meson.build

@@ -25,6 +25,7 @@ src = [
     'src/server.c',
     'src/stream.c',
     'src/video_buffer.c',
+    'src/util/acksync.c',
     'src/util/file.c',
     'src/util/intr.c',
     'src/util/log.c',

app/src/util/acksync.c

@@ -0,0 +1,76 @@
+#include "acksync.h"
+
+#include <assert.h>
+#include "util/log.h"
+
+bool
+sc_acksync_init(struct sc_acksync *as) {
+    bool ok = sc_mutex_init(&as->mutex);
+    if (!ok) {
+        return false;
+    }
+
+    ok = sc_cond_init(&as->cond);
+    if (!ok) {
+        sc_mutex_destroy(&as->mutex);
+        return false;
+    }
+
+    as->stopped = false;
+    as->ack = SC_SEQUENCE_INVALID;
+
+    return true;
+}
+
+void
+sc_acksync_destroy(struct sc_acksync *as) {
+    sc_cond_destroy(&as->cond);
+    sc_mutex_destroy(&as->mutex);
+}
+
+void
+sc_acksync_ack(struct sc_acksync *as, uint64_t sequence) {
+    sc_mutex_lock(&as->mutex);
+
+    // Acknowledgements must be monotonic
+    assert(sequence >= as->ack);
+
+    as->ack = sequence;
+    sc_cond_signal(&as->cond);
+
+    sc_mutex_unlock(&as->mutex);
+}
+
+enum sc_acksync_wait_result
+sc_acksync_wait(struct sc_acksync *as, uint64_t ack, sc_tick deadline) {
+    sc_mutex_lock(&as->mutex);
+
+    bool timed_out = false;
+    while (!as->stopped && as->ack < ack && !timed_out) {
+        timed_out = !sc_cond_timedwait(&as->cond, &as->mutex, deadline);
+    }
+
+    enum sc_acksync_wait_result ret;
+    if (as->stopped) {
+        ret = SC_ACKSYNC_WAIT_INTR;
+    } else if (as->ack >= ack) {
+        ret = SC_ACKSYNC_WAIT_OK;
+    } else {
+        assert(timed_out);
+        ret = SC_ACKSYNC_WAIT_TIMEOUT;
+    }
+    sc_mutex_unlock(&as->mutex);
+
+    return ret;
+}
+
+/**
+ * Interrupt any `sc_acksync_wait()`
+ */
+void
+sc_acksync_interrupt(struct sc_acksync *as) {
+    sc_mutex_lock(&as->mutex);
+    as->stopped = true;
+    sc_cond_signal(&as->cond);
+    sc_mutex_unlock(&as->mutex);
+}

app/src/util/acksync.h

@@ -0,0 +1,61 @@
+#ifndef SC_ACK_SYNC_H
+#define SC_ACK_SYNC_H
+
+#include "common.h"
+
+#include "thread.h"
+
+#define SC_SEQUENCE_INVALID 0
+
+/**
+ * Helper to wait for acknowledgments
+ */
+struct sc_acksync {
+    sc_mutex mutex;
+    sc_cond cond;
+
+    bool stopped;
+
+    // Last acked value, initially SC_SEQUENCE_INVALID
+    uint64_t ack;
+};
+
+enum sc_acksync_wait_result {
+    // Acknowledgment received
+    SC_ACKSYNC_WAIT_OK,
+
+    // Timeout expired
+    SC_ACKSYNC_WAIT_TIMEOUT,
+
+    // Interrupted from another thread by sc_acksync_interrupt()
+    SC_ACKSYNC_WAIT_INTR,
+};
+
+bool
+sc_acksync_init(struct sc_acksync *as);
+
+void
+sc_acksync_destroy(struct sc_acksync *as);
+
+/**
+ * Acknowledge `sequence`
+ *
+ * The `sequence` must be greater than (or equal to) any previous acknowledged
+ * sequence.
+ */
+void
+sc_acksync_ack(struct sc_acksync *as, uint64_t sequence);
+
+/**
+ * Wait for acknowledgment of sequence `ack` (or higher)
+ */
+enum sc_acksync_wait_result
+sc_acksync_wait(struct sc_acksync *as, uint64_t ack, sc_tick deadline);
+
+/**
+ * Interrupt any `sc_acksync_wait()`
+ */
+void
+sc_acksync_interrupt(struct sc_acksync *as);
+
+#endif