3 files changed, 148 insertions, 0 deletions
diff --git a/include/qemu/co-shared-resource.h b/include/qemu/co-shared-resource.h
new file mode 100644
index 0000000..4e45030
--- /dev/null
+++ b/include/qemu/co-shared-resource.h
@@ -0,0 +1,71 @@
+/*
+ * Helper functionality for distributing a fixed total amount of
+ * an abstract resource among multiple coroutines.
+ *
+ * Copyright (c) 2019 Virtuozzo International GmbH
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+#ifndef QEMU_CO_SHARED_RESOURCE_H
+#define QEMU_CO_SHARED_RESOURCE_H
+
+
+typedef struct SharedResource SharedResource;
+
+/*
+ * Create SharedResource structure
+ *
+ * @total: total amount of some resource to be shared between clients
+ *
+ * Note: this API is not thread-safe.
+ */
+SharedResource *shres_create(uint64_t total);
+
+/*
+ * Release SharedResource structure
+ *
+ * This function may only be called once everything allocated by all
+ * clients has been deallocated.
+ */
+void shres_destroy(SharedResource *s);
+
+/*
+ * Try to allocate an amount of @n.  Return true on success, and false
+ * if there is too little left of the collective resource to fulfill
+ * the request.
+ */
+bool co_try_get_from_shres(SharedResource *s, uint64_t n);
+
+/*
+ * Allocate an amount of @n, and, if necessary, yield until
+ * that becomes possible.
+ */
+void coroutine_fn co_get_from_shres(SharedResource *s, uint64_t n);
+
+/*
+ * Deallocate an amount of @n.  The total amount allocated by a caller
+ * does not need to be deallocated/released with a single call, but may
+ * be split over several calls.  For example, get(4), get(3), and then
+ * put(5), put(2).
+ */
+void coroutine_fn co_put_to_shres(SharedResource *s, uint64_t n);
+
+
+#endif /* QEMU_CO_SHARED_RESOURCE_H */
diff --git a/util/Makefile.objs b/util/Makefile.objs
index 41bf59d..df124af 100644
--- a/util/Makefile.objs
+++ b/util/Makefile.objs
@@ -37,6 +37,7 @@ util-obj-y += rcu.o
 util-obj-$(CONFIG_MEMBARRIER) += sys_membarrier.o
 util-obj-y += qemu-coroutine.o qemu-coroutine-lock.o qemu-coroutine-io.o
 util-obj-y += qemu-coroutine-sleep.o
+util-obj-y += qemu-co-shared-resource.o
 util-obj-y += coroutine-$(CONFIG_COROUTINE_BACKEND).o
 util-obj-y += buffer.o
 util-obj-y += timed-average.o
diff --git a/util/qemu-co-shared-resource.c b/util/qemu-co-shared-resource.c
new file mode 100644
index 0000000..1c83cd9
--- /dev/null
+++ b/util/qemu-co-shared-resource.c
@@ -0,0 +1,76 @@
+/*
+ * Helper functionality for distributing a fixed total amount of
+ * an abstract resource among multiple coroutines.
+ *
+ * Copyright (c) 2019 Virtuozzo International GmbH
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+#include "qemu/osdep.h"
+#include "qemu/coroutine.h"
+#include "qemu/co-shared-resource.h"
+
+struct SharedResource {
+    uint64_t total;
+    uint64_t available;
+
+    CoQueue queue;
+};
+
+SharedResource *shres_create(uint64_t total)
+{
+    SharedResource *s = g_new0(SharedResource, 1);
+
+    s->total = s->available = total;
+    qemu_co_queue_init(&s->queue);
+
+    return s;
+}
+
+void shres_destroy(SharedResource *s)
+{
+    assert(s->available == s->total);
+    g_free(s);
+}
+
+bool co_try_get_from_shres(SharedResource *s, uint64_t n)
+{
+    if (s->available >= n) {
+        s->available -= n;
+        return true;
+    }
+
+    return false;
+}
+
+void coroutine_fn co_get_from_shres(SharedResource *s, uint64_t n)
+{
+    assert(n <= s->total);
+    while (!co_try_get_from_shres(s, n)) {
+        qemu_co_queue_wait(&s->queue, NULL);
+    }
+}
+
+void coroutine_fn co_put_to_shres(SharedResource *s, uint64_t n)
+{
+    assert(s->total - s->available >= n);
+    s->available += n;
+    qemu_co_queue_restart_all(&s->queue);
+}