From 53d87c743a5f2fe174c18d63bb2e4b4a582877b5 Mon Sep 17 00:00:00 2001
From: Julio Biason <j.biason@engys.com>
Date: Fri, 28 Oct 2022 11:20:58 -0300
Subject: [PATCH] Made a resource manager

---
 resman.py | 75 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 75 insertions(+)
 create mode 100644 resman.py

diff --git a/resman.py b/resman.py
new file mode 100644
index 0000000..6a48ba4
--- /dev/null
+++ b/resman.py
@@ -0,0 +1,75 @@
+"""Resource Manager."""
+
+import logging
+import time
+
+from threading import Condition
+from threading import Lock
+from threading import Thread
+
+
+LOGGER = logging.getLogger(__name__)
+
+
+class Resource:
+    def __init__(self, manager, resources: int):
+        self._manager = manager
+        self._resources = resources
+
+    def release(self):
+        LOGGER.debug("Resource of %d will be returned", self._resources)
+        self._manager.release(self._resources)
+
+    @property
+    def resources(self):
+        return self._resources
+
+
+class ResourceManager:
+    def __init__(self, total_resources: int):
+        self._total_resources = total_resources
+        self._cond = Condition(Lock())
+        LOGGER.debug("Created a manager with %d resources", self._total_resources)
+
+    def grab(self, resources: int):
+        """Grab a number of resources; if there are not enough resources
+        available, blocks till they become available.
+        """
+        LOGGER.debug("Requesting %d resources; %d avaialble", resources, self._total_resources)
+        with self._cond:
+            self._cond.wait_for(lambda : self._total_resources >= resources)
+            self._total_resources -= resources
+        return Resource(self, resources)
+
+    def release(self, resources: int):
+        """Return the number of resources to the pool."""
+        with self._cond:
+            self._total_resources += resources
+            self._cond.notify()
+        LOGGER.debug("%d resources returned, %d available", resources, self._total_resources)
+
+
+def worker(pid, resources):
+    LOGGER.debug("Thread %d is holding %d resources", pid, resources.resources)
+    time.sleep(10)
+    LOGGER.debug("Thread %d finished, releasing %d resources", pid, resources.resources)
+    resources.release()
+
+
+def main():
+    logging.basicConfig(level=logging.DEBUG)
+    manager = ResourceManager(10)
+    threads = []
+
+    for i in range(10):
+        resources = manager.grab(i+1)
+        w = Thread(target=worker, args=[i, resources])
+        threads.append(w)
+        w.start()
+
+    for t in threads:
+        t.join()
+
+
+if __name__ == '__main__':
+    main()