[rvm-research] Implementation of setPriority/getPriority for RVMThread (RVM-750)

diff -r 6ea4feda95a5 rvm/src/org/jikesrvm/VM.java
--- a/rvm/src/org/jikesrvm/VM.java	Mon Jul 22 19:47:09 2013 +0200
+++ b/rvm/src/org/jikesrvm/VM.java	Wed Jul 24 14:14:44 2013 +0100
@@ -160,6 +160,7 @@
     //
     sysCall.sysSetupHardwareTrapHandler();
     RVMThread.getCurrentThread().pthread_id = sysCall.sysGetThreadId();
+    RVMThread.getCurrentThread().priority_handle = sysCall.sysGetThreadPriorityHandle();
     RVMThread.availableProcessors = SysCall.sysCall.sysNumProcessors();
 
     // Set up buffer locks used by Thread for logging and status dumping.
diff -r 6ea4feda95a5 rvm/src/org/jikesrvm/runtime/BootRecord.java
--- a/rvm/src/org/jikesrvm/runtime/BootRecord.java	Mon Jul 22 19:47:09 2013 +0200
+++ b/rvm/src/org/jikesrvm/runtime/BootRecord.java	Wed Jul 24 14:14:44 2013 +0100
@@ -262,6 +262,9 @@
   public Address sysSetupHardwareTrapHandlerIP;
   public Address sysStashVMThreadIP;
   public Address sysThreadTerminateIP;
+  public Address sysGetThreadPriorityHandleIP;
+  public Address sysGetThreadPriorityIP;
+  public Address sysSetThreadPriorityIP;
 
   // monitors
   public Address sysMonitorCreateIP;
diff -r 6ea4feda95a5 rvm/src/org/jikesrvm/runtime/SysCall.java
--- a/rvm/src/org/jikesrvm/runtime/SysCall.java	Mon Jul 22 19:47:09 2013 +0200
+++ b/rvm/src/org/jikesrvm/runtime/SysCall.java	Wed Jul 24 14:14:44 2013 +0100
@@ -190,6 +190,15 @@
   public abstract Word sysGetThreadId();
 
   @SysCallTemplate
+  public abstract Word sysGetThreadPriorityHandle();
+  
+  @SysCallTemplate
+  public abstract int sysGetThreadPriority(Word thread, Word handle);
+  
+  @SysCallTemplate
+  public abstract int sysSetThreadPriority(Word thread, Word handle, int priority);
+  
+  @SysCallTemplate
   public abstract void sysSetupHardwareTrapHandler();
 
   // This implies that the RVMThread is somehow pinned, or else the
diff -r 6ea4feda95a5 rvm/src/org/jikesrvm/scheduler/RVMThread.java
--- a/rvm/src/org/jikesrvm/scheduler/RVMThread.java	Mon Jul 22 19:47:09 2013 +0200
+++ b/rvm/src/org/jikesrvm/scheduler/RVMThread.java	Wed Jul 24 14:14:44 2013 +0100
@@ -1025,6 +1025,12 @@
   public Word pthread_id;
 
   /**
+   * Thread priority handle.  Used when manipulating the threads priority.
+   * This may be different from pthread_id.
+   */
+  public Word priority_handle;
+  
+  /**
    * Scratch area for use for gpr <=> fpr transfers by PPC baseline compiler.
    * Used to transfer x87 to SSE registers on IA32
    */
@@ -2590,6 +2596,14 @@
      * get pthread_id from the operating system and store into RVMThread field
      */
     currentThread.pthread_id = sysCall.sysGetThreadId();
+    currentThread.priority_handle = sysCall.sysGetThreadPriorityHandle();
+    
+    /* 
+     * set thread priority to match stored value
+     */
+    sysCall.sysSetThreadPriority(currentThread.pthread_id, 
+        currentThread.priority_handle, currentThread.priority - Thread.NORM_PRIORITY);
+    
     currentThread.enableYieldpoints();
     sysCall.sysStashVMThread(currentThread);
     if (traceAcct) {
@@ -4471,6 +4485,10 @@
    * @see java.lang.Thread#getPriority()
    */
   public int getPriority() {
+    if (isAlive()) {
+      // compute current priority
+      priority = sysCall.sysGetThreadPriority(pthread_id, priority_handle) + Thread.NORM_PRIORITY;
+    }
     return priority;
   }
 
@@ -4481,8 +4499,15 @@
    * @see java.lang.Thread#getPriority()
    */
   public void setPriority(int priority) {
-    this.priority = priority;
-    // @TODO this should be calling a syscall
+    if (isAlive()) {
+      if (sysCall.sysSetThreadPriority(pthread_id, priority_handle, priority - Thread.NORM_PRIORITY) == 0) {
+        this.priority = priority;
+      } else {
+        // setting priority failed
+      }
+    } else {
+      this.priority = priority;
+    }
   }
 
   /**
diff -r 6ea4feda95a5 tools/bootImageRunner/sys.C
--- a/tools/bootImageRunner/sys.C	Mon Jul 22 19:47:09 2013 +0200
+++ b/tools/bootImageRunner/sys.C	Wed Jul 24 14:14:44 2013 +0100
@@ -34,6 +34,11 @@
 extern "C" int sched_yield(void);
 #endif
 
+// Enable syscall on Linux / glibc
+#ifdef RVM_FOR_LINUX
+#define _GNU_SOURCE
+#endif
+
 #include <stdio.h>
 #include <stdlib.h>      // getenv() and others
 #include <unistd.h>
@@ -71,6 +76,7 @@
 #include <sys/ioctl.h>
 #ifdef RVM_FOR_LINUX
 #include <asm/ioctls.h>
+#include <sys/syscall.h>
 #endif
 
 # include <sched.h>
@@ -1248,6 +1254,104 @@
 #endif
 }
 
+// Determine if a given thread can use pthread_setschedparam to
+// configure its priority, this is based on the current priority
+// of the thread.
+//
+// The result will be true on all systems other than Linux where
+// pthread_setschedparam cannot be used with SCHED_OTHER policy.
+//
+static int hasPthreadPriority(Word thread_id)
+{
+    struct sched_param param;
+    int policy;
+    if (!pthread_getschedparam((pthread_t)thread_id, &policy, &param)) {
+        int min = sched_get_priority_min(policy);
+        int max = sched_get_priority_max(policy);
+        if (min || max) {
+            return 1;
+        }
+    }
+    return 0;
+}
+
+// Return a handle which can be used to manipulate a threads priority
+// on Linux this will be the kernel thread_id, on other systems the
+// standard thread id.
+extern "C" Word
+sysGetThreadPriorityHandle()
+{
+    // gettid() syscall is Linux specific, detect its syscall number macro
+    #ifdef SYS_gettid
+    pid_t tid = (pid_t) syscall(SYS_gettid);
+    if (tid != -1)
+        return (Word) tid;
+    #endif /* SYS_gettid */
+    return (Word) getThreadId();
+}
+
+// Compute the default (or middle) priority for a given policy.
+static int defaultPriority(int policy)
+{
+    int min = sched_get_priority_min(policy);
+    int max = sched_get_priority_max(policy);
+    return min + ((max - min) / 2);
+}
+
+// Get the thread priority as an offset from the default.
+extern "C" int
+sysGetThreadPriority(Word thread, Word handle)
+{
+    // use pthread priority mechanisms where possible
+    if (hasPthreadPriority(thread)) {
+        struct sched_param param;
+        int policy;
+        if (!pthread_getschedparam((pthread_t)thread, &policy, &param)) {
+            return param.sched_priority - defaultPriority(policy);
+        }
+    } else if (thread != handle) {
+        // fallback to setpriority if handle is valid
+        // i.e. handle is tid from gettid()
+        int result;
+        errno = 0; // as result can be legally be -1
+        result = getpriority(PRIO_PROCESS, (int) handle);
+        if (errno == 0) {
+            // default priority is 0, low number -> high priority
+            return -result;
+        }
+
+    }
+    return 0;
+}
+
+// Set the thread priority as an offset from the default.
+extern "C" int
+sysSetThreadPriority(Word thread, Word handle, int priority)
+{
+    // fast path
+    if (sysGetThreadPriority(thread, handle) == priority)
+        return 0;
+
+    // use pthread priority mechanisms where possible
+    if (hasPthreadPriority(thread)) {
+        struct sched_param param;
+        int policy;
+        int result = pthread_getschedparam((pthread_t)thread, &policy, &param);
+        if (!result) {
+            param.sched_priority = defaultPriority(policy) + priority;
+            return pthread_setschedparam((pthread_t)thread, policy, &param);
+        } else {
+            return result;
+        }
+    } else if (thread != handle) {
+        // fallback to setpriority if handle is valid
+        // i.e. handle is tid from gettid()
+        // default priority is 0, low number -> high priority
+        return setpriority(PRIO_PROCESS, (int) handle, -priority);
+    }
+    return -1;
+}
+
 ////////////// Pthread mutex and condition functions /////////////
 
 #ifndef RVM_FOR_HARMONY