libbinder: RPC remove isTriggeredPolled

We can get this information in-process, so we can avoid the syscall (and
due to the way it is implemented, we also don't need locking).

Bug: 182940634
Test: binderRpcTest
Change-Id: I3a4f683f71f54972509e071f5dd349e15de54b08

3 files changed, 7 insertions, 39 deletions

diff --git a/libs/binder/FdTrigger.cpp b/libs/binder/FdTrigger.cpp
index b197a6aa8d..ecf13dc583 100644
--- a/libs/binder/FdTrigger.cpp
+++ b/libs/binder/FdTrigger.cpp
@@ -59,19 +59,4 @@ status_t FdTrigger::triggerablePoll(base::borrowed_fd fd, int16_t event) {
     }
 }
 
-android::base::Result<bool> FdTrigger::isTriggeredPolled() {
-    pollfd pfd{.fd = mRead.get(), .events = 0, .revents = 0};
-    int ret = TEMP_FAILURE_RETRY(poll(&pfd, 1, 0));
-    if (ret < 0) {
-        return android::base::ErrnoError() << "FdTrigger::isTriggeredPolled: Error in poll()";
-    }
-    if (ret == 0) {
-        return false;
-    }
-    if (pfd.revents & POLLHUP) {
-        return true;
-    }
-    return android::base::Error() << "FdTrigger::isTriggeredPolled: poll() returns " << pfd.revents;
-}
-
 } // namespace android
diff --git a/libs/binder/FdTrigger.h b/libs/binder/FdTrigger.h
index 5f67ba3188..a545d6cbea 100644
--- a/libs/binder/FdTrigger.h
+++ b/libs/binder/FdTrigger.h
@@ -35,7 +35,11 @@ public:
     void trigger();
 
     /**
-     * Check whether this has been triggered by checking the write end.
+     * Check whether this has been triggered by checking the write end. Note:
+     * this has no internal locking, and it is inherently racey, but this is
+     * okay, because if we accidentally return false when a trigger has already
+     * happened, we can imagine that instead, the scheduler actually executed
+     * the code which is polling isTriggered earlier.
      */
     [[nodiscard]] bool isTriggered();
 
@@ -50,16 +54,6 @@ public:
      */
     [[nodiscard]] status_t triggerablePoll(base::borrowed_fd fd, int16_t event);
 
-    /**
-     * Check whether this has been triggered by poll()ing the read end.
-     *
-     * Return:
-     *   true - triggered
-     *   false - not triggered
-     *   error - error when polling
-     */
-    [[nodiscard]] android::base::Result<bool> isTriggeredPolled();
-
 private:
     base::unique_fd mWrite;
     base::unique_fd mRead;
diff --git a/libs/binder/RpcTransportTls.cpp b/libs/binder/RpcTransportTls.cpp
index 63f93391e5..23088ad60e 100644
--- a/libs/binder/RpcTransportTls.cpp
+++ b/libs/binder/RpcTransportTls.cpp
@@ -319,8 +319,6 @@ public:
 private:
     android::base::unique_fd mSocket;
     Ssl mSsl;
-
-    static status_t isTriggered(FdTrigger* fdTrigger);
 };
 
 // Error code is errno.
@@ -341,15 +339,6 @@ Result<size_t> RpcTransportTls::peek(void* buf, size_t size) {
     return ret;
 }
 
-status_t RpcTransportTls::isTriggered(FdTrigger* fdTrigger) {
-    auto ret = fdTrigger->isTriggeredPolled();
-    if (!ret.ok()) {
-        ALOGE("%s: %s", __PRETTY_FUNCTION__, ret.error().message().c_str());
-        return ret.error().code() == 0 ? UNKNOWN_ERROR : -ret.error().code();
-    }
-    return *ret ? -ECANCELED : OK;
-}
-
 status_t RpcTransportTls::interruptableWriteFully(FdTrigger* fdTrigger, const void* data,
                                                   size_t size) {
     auto buffer = reinterpret_cast<const uint8_t*>(data);
@@ -359,7 +348,7 @@ status_t RpcTransportTls::interruptableWriteFully(FdTrigger* fdTrigger, const vo
 
     // Before doing any I/O, check trigger once. This ensures the trigger is checked at least
     // once. The trigger is also checked via triggerablePoll() after every SSL_write().
-    if (status_t status = isTriggered(fdTrigger); status != OK) return status;
+    if (fdTrigger->isTriggered()) return -ECANCELED;
 
     while (buffer < end) {
         size_t todo = std::min<size_t>(end - buffer, std::numeric_limits<int>::max());
@@ -390,7 +379,7 @@ status_t RpcTransportTls::interruptableReadFully(FdTrigger* fdTrigger, void* dat
 
     // Before doing any I/O, check trigger once. This ensures the trigger is checked at least
     // once. The trigger is also checked via triggerablePoll() after every SSL_write().
-    if (status_t status = isTriggered(fdTrigger); status != OK) return status;
+    if (fdTrigger->isTriggered()) return -ECANCELED;
 
     while (buffer < end) {
         size_t todo = std::min<size_t>(end - buffer, std::numeric_limits<int>::max());