From ab99af7ca7fb96460a28d9691c788e1157d1c9cf Mon Sep 17 00:00:00 2001
From: Oliver Giles <ohw.giles@gmail.com>
Date: Thu, 10 Aug 2017 07:40:30 +0300
Subject: [PATCH] implement general-purpose locks

---
 src/client.cpp    |  8 ++++++++
 src/laminar.capnp |  2 ++
 src/server.cpp    | 39 +++++++++++++++++++++++++++++++++++++++
 3 files changed, 49 insertions(+)

diff --git a/src/client.cpp b/src/client.cpp
index af3af2b..7e4ccdc 100644
--- a/src/client.cpp
+++ b/src/client.cpp
@@ -158,6 +158,14 @@ int main(int argc, char** argv) {
         auto response = req.send().wait(waitScope);
         if(response.getResult() != LaminarCi::JobResult::SUCCESS)
             return EFAILED;
+    } else if(strcmp(argv[1], "lock") == 0) {
+        auto req = laminar.lockRequest();
+        req.setLockName(argv[2]);
+        req.send().wait(waitScope);
+    } else if(strcmp(argv[1], "release") == 0) {
+        auto req = laminar.releaseRequest();
+        req.setLockName(argv[2]);
+        req.send().wait(waitScope);
     } else {
         fprintf(stderr, "Unknown comand %s\n", argv[1]);
         return EINVAL;
diff --git a/src/laminar.capnp b/src/laminar.capnp
index 25ffdc7..f947bf4 100644
--- a/src/laminar.capnp
+++ b/src/laminar.capnp
@@ -6,6 +6,8 @@ interface LaminarCi {
     start @1 (jobName :Text, params :List(JobParam)) -> (result :JobResult);
     pend @2 (jobName :Text, buildNum :UInt32) -> (result :JobResult);
     set @3 (jobName :Text, buildNum :UInt32, param :JobParam) -> (result :MethodResult);
+    lock @4 (lockName :Text) -> ();
+    release @5 (lockName :Text) -> ();
 
     struct JobParam {
         name @0 :Text;
diff --git a/src/server.cpp b/src/server.cpp
index a4547af..8b8785c 100644
--- a/src/server.cpp
+++ b/src/server.cpp
@@ -75,6 +75,18 @@ LaminarCi::JobResult fromRunState(RunState state) {
 // As such, it implements the pure virtual interface generated from
 // laminar.capnp with calls to the LaminarInterface
 class RpcImpl : public LaminarCi::Server {
+private:
+    struct Lock {
+        Lock() : paf(kj::newPromiseAndFulfiller<void>()) {}
+        void release() {
+            paf.fulfiller->fulfill();
+        }
+        kj::Promise<void> takePromise() { return std::move(paf.promise); }
+    private:
+        kj::PromiseFulfillerPair<void> paf;
+    };
+
+
 public:
     RpcImpl(LaminarInterface& l) :
         LaminarCi::Server(),
@@ -143,9 +155,36 @@ public:
         return kj::READY_NOW;
     }
 
+    // Take a named lock
+    kj::Promise<void> lock(LockContext context) override {
+        std::string lockName = context.getParams().getLockName();
+        LLOG(INFO, "RPC lock", lockName);
+        auto& lockList = locks[lockName];
+        lockList.emplace_back(Lock{});
+        if(lockList.size() == 1)
+            lockList.front().release();
+        return lockList.back().takePromise();
+    }
+
+    // Release a named lock
+    kj::Promise<void> release(ReleaseContext context) override {
+        std::string lockName = context.getParams().getLockName();
+        LLOG(INFO, "RPC release", lockName);
+        auto& lockList = locks[lockName];
+        if(lockList.size() == 0) {
+            LLOG(INFO, "Attempt to release unheld lock", lockName);
+            return kj::READY_NOW;
+        }
+        lockList.erase(lockList.begin());
+        if(lockList.size() > 0)
+            lockList.front().release();
+        return kj::READY_NOW;
+    }
+
 private:
     LaminarInterface& laminar;
     kj::LowLevelAsyncIoProvider* asyncio;
+    std::unordered_map<std::string, std::list<Lock>> locks;
 };