Tue, 11 Nov 2014 11:05:41 +0100
8056071: compiler/whitebox/IsMethodCompilableTest.java fails with 'method() is not compilable after 3 iterations'
Summary: Always use MDO if valid and always compile trivial methods with C1 if available.
Reviewed-by: kvn, iveresov
1 /*
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25 #include "precompiled.hpp"
26 #include "runtime/basicLock.hpp"
27 #include "runtime/synchronizer.hpp"
29 void BasicLock::print_on(outputStream* st) const {
30 st->print("monitor");
31 }
33 void BasicLock::move_to(oop obj, BasicLock* dest) {
34 // Check to see if we need to inflate the lock. This is only needed
35 // if an object is locked using "this" lightweight monitor. In that
36 // case, the displaced_header() is unlocked, because the
37 // displaced_header() contains the header for the originally unlocked
38 // object. However the object could have already been inflated. But it
39 // does not matter, the inflation will just a no-op. For other cases,
40 // the displaced header will be either 0x0 or 0x3, which are location
41 // independent, therefore the BasicLock is free to move.
42 //
43 // During OSR we may need to relocate a BasicLock (which contains a
44 // displaced word) from a location in an interpreter frame to a
45 // new location in a compiled frame. "this" refers to the source
46 // basiclock in the interpreter frame. "dest" refers to the destination
47 // basiclock in the new compiled frame. We *always* inflate in move_to().
48 // The always-Inflate policy works properly, but in 1.5.0 it can sometimes
49 // cause performance problems in code that makes heavy use of a small # of
50 // uncontended locks. (We'd inflate during OSR, and then sync performance
51 // would subsequently plummet because the thread would be forced thru the slow-path).
52 // This problem has been made largely moot on IA32 by inlining the inflated fast-path
53 // operations in Fast_Lock and Fast_Unlock in i486.ad.
54 //
55 // Note that there is a way to safely swing the object's markword from
56 // one stack location to another. This avoids inflation. Obviously,
57 // we need to ensure that both locations refer to the current thread's stack.
58 // There are some subtle concurrency issues, however, and since the benefit is
59 // is small (given the support for inflated fast-path locking in the fast_lock, etc)
60 // we'll leave that optimization for another time.
62 if (displaced_header()->is_neutral()) {
63 ObjectSynchronizer::inflate_helper(obj);
64 // WARNING: We can not put check here, because the inflation
65 // will not update the displaced header. Once BasicLock is inflated,
66 // no one should ever look at its content.
67 } else {
68 // Typically the displaced header will be 0 (recursive stack lock) or
69 // unused_mark. Naively we'd like to assert that the displaced mark
70 // value is either 0, neutral, or 3. But with the advent of the
71 // store-before-CAS avoidance in fast_lock/compiler_lock_object
72 // we can find any flavor mark in the displaced mark.
73 }
74 // [RGV] The next line appears to do nothing!
75 intptr_t dh = (intptr_t) displaced_header();
76 dest->set_displaced_header(displaced_header());
77 }