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src/hotspot/share/runtime/basicLock.cpp

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  44   // independent, therefore the BasicLock is free to move.
  45   //
  46   // During OSR we may need to relocate a BasicLock (which contains a
  47   // displaced word) from a location in an interpreter frame to a
  48   // new location in a compiled frame.  "this" refers to the source
  49   // basiclock in the interpreter frame.  "dest" refers to the destination
  50   // basiclock in the new compiled frame.  We *always* inflate in move_to().
  51   // The always-Inflate policy works properly, but in 1.5.0 it can sometimes
  52   // cause performance problems in code that makes heavy use of a small # of
  53   // uncontended locks.   (We'd inflate during OSR, and then sync performance
  54   // would subsequently plummet because the thread would be forced thru the slow-path).
  55   // This problem has been made largely moot on IA32 by inlining the inflated fast-path
  56   // operations in Fast_Lock and Fast_Unlock in i486.ad.
  57   //
  58   // Note that there is a way to safely swing the object's markword from
  59   // one stack location to another.  This avoids inflation.  Obviously,
  60   // we need to ensure that both locations refer to the current thread's stack.
  61   // There are some subtle concurrency issues, however, and since the benefit is
  62   // is small (given the support for inflated fast-path locking in the fast_lock, etc)
  63   // we'll leave that optimization for another time.




  64 
  65   if (displaced_header()->is_neutral()) {
  66     ObjectSynchronizer::inflate_helper(obj);
  67     // WARNING: We can not put check here, because the inflation
  68     // will not update the displaced header. Once BasicLock is inflated,
  69     // no one should ever look at its content.
  70   } else {
  71     // Typically the displaced header will be 0 (recursive stack lock) or
  72     // unused_mark.  Naively we'd like to assert that the displaced mark
  73     // value is either 0, neutral, or 3.  But with the advent of the
  74     // store-before-CAS avoidance in fast_lock/compiler_lock_object
  75     // we can find any flavor mark in the displaced mark.
  76   }
  77 // [RGV] The next line appears to do nothing!
  78   intptr_t dh = (intptr_t) displaced_header();
  79   dest->set_displaced_header(displaced_header());
  80 }


  44   // independent, therefore the BasicLock is free to move.
  45   //
  46   // During OSR we may need to relocate a BasicLock (which contains a
  47   // displaced word) from a location in an interpreter frame to a
  48   // new location in a compiled frame.  "this" refers to the source
  49   // basiclock in the interpreter frame.  "dest" refers to the destination
  50   // basiclock in the new compiled frame.  We *always* inflate in move_to().
  51   // The always-Inflate policy works properly, but in 1.5.0 it can sometimes
  52   // cause performance problems in code that makes heavy use of a small # of
  53   // uncontended locks.   (We'd inflate during OSR, and then sync performance
  54   // would subsequently plummet because the thread would be forced thru the slow-path).
  55   // This problem has been made largely moot on IA32 by inlining the inflated fast-path
  56   // operations in Fast_Lock and Fast_Unlock in i486.ad.
  57   //
  58   // Note that there is a way to safely swing the object's markword from
  59   // one stack location to another.  This avoids inflation.  Obviously,
  60   // we need to ensure that both locations refer to the current thread's stack.
  61   // There are some subtle concurrency issues, however, and since the benefit is
  62   // is small (given the support for inflated fast-path locking in the fast_lock, etc)
  63   // we'll leave that optimization for another time.
  64   if (obj->is_value()) {
  65     // Ignore value types
  66     return;
  67   }
  68 
  69   if (displaced_header()->is_neutral()) {
  70     ObjectSynchronizer::inflate_helper(obj);
  71     // WARNING: We can not put check here, because the inflation
  72     // will not update the displaced header. Once BasicLock is inflated,
  73     // no one should ever look at its content.
  74   } else {
  75     // Typically the displaced header will be 0 (recursive stack lock) or
  76     // unused_mark.  Naively we'd like to assert that the displaced mark
  77     // value is either 0, neutral, or 3.  But with the advent of the
  78     // store-before-CAS avoidance in fast_lock/compiler_lock_object
  79     // we can find any flavor mark in the displaced mark.
  80   }
  81 // [RGV] The next line appears to do nothing!
  82   intptr_t dh = (intptr_t) displaced_header();
  83   dest->set_displaced_header(displaced_header());
  84 }
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